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Select this Article		On Lateral Deflection of Horizontally Loaded Rigid Piles in Elastoplastic Medium Ernesto Motta Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000771 Posted ahead of print 16 May 2012 Full Text: \| Download PDF
	+ -	Show Abstract The paper deals with the design of rigid piles under lateral load. In many practical situations the pile displacements could be the limiting factor for the design, thus an allowable displacement analysis instead of an allowable stress analysis could be more appropriate in the foundation design. A non linear elastoplastic closed form solution for the evaluation of the response of rigid piles under lateral load is presented. The derived equations allow to determine the lateral displacement and the load distribution for a given combination of the applied forces H₀ and M₀ at the pile head. The approach can be applied either for cohesive or cohesionless soils. For a greater generality the solution has been given in a non dimensional form. A comparison with the Broms solution for a free rigid pile in cohesionless soil is also presented. Comparisons with experimental results show that the proposed approach may fit in a reliable way the non linear load‐displacement response of a free rigid pile.

Select this Article		Correcting Liquefaction Resistance of Unsaturated Soil Using Wave Velocity Akhter M. Hossain, Ronald D. Andrus, M. ASCE, and William M. Camp, III, M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000770 Posted ahead of print 16 May 2012 Full Text: \| Download PDF
	+ -	Show Abstract Explicit empirical relationships for correcting liquefaction resistance of unsaturated soil below the groundwater table using compression wave velocity (V_P) and shear wave velocity (V_S) are derived and evaluated in this paper. The relationships are derived using published laboratory test data for four different sands and one silt material. The laboratory test data based on V_P exhibit less scatter than the test data based on the ratio V_P/V_S. For this reason, the V_P‐based relationship is recommended for correcting the liquefaction resistance of unsaturated soil. The influence of loading cycles and relative density on the recommended relationship is investigated. From a review of forty field case history sites, it is found that in the critical layers at 20% of the sites average V_P is less than 1,400 m/s, indicating unsaturated conditions. Liquefaction resistances computed for eight field case histories with V_P < 1,200 m/s in the critical layers are corrected and plotted on penetration‐ and V_S‐based liquefaction evaluation charts. The results support the use of the correction for unsaturated conditions below the groundwater table.

Select this Article		Centrifuge Modeling and Mitigation of Manhole Uplift Due to Liquefaction Gi‐Chun Kang, Tetsuo Tobita, Susumu Iai, and Louis Ge Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000769 Posted ahead of print 16 May 2012 Full Text: \| Download PDF
	+ -	Show Abstract Since low‐compacted trench backfill around a manhole is normally liquefiable, the manhole could suffer uplift damage associated with soil liquefaction during strong earthquake. In this study, twenty two dynamic centrifuge model tests were carried out to investigate the response of a buried manhole subjected to a dynamic load. The models were tested under 20 g and a substitute pore fluid was used to avoid scaling law conflict between the dynamic and diffusion processes. It was found that the excess pore water pressure is one of the contributing factors to the magnitude of the manhole uplift. With that, new mitigation methods against the uplift in liquefied ground were developed. Their effectiveness was also examined through the tests. A model manhole mitigated with the proposed methods was tested in pair with a regular model manhole. From the test results, the magnitude of manhole uplifts with the mitigation methods decreased as build‐up of the excess pore water pressure was restrained in high‐compacted backfill or excess pore water was dissipated into the manhole during strong shaking.

Select this Article		The Role of Particle Angularity on the Mechanical Behavior of Granular Mixtures H. Shin and J. C. Santamarina Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000768 Posted ahead of print 16 May 2012 Full Text: \| Download PDF
	+ -	Show Abstract Particle shape affects the mechanical behavior of soils, including packing density, stiffness, volume change during shear, and strength. Laboratory experiments conducted to study the mechanical response of sand mixtures made of round and angular grains show the increase in void ratio, small strain shear modulus G_max (constant fabric), oedometric compressibility C_C (fabric changes), and in friction angle, but a decrease in lateral stress coefficient k₀ as the mass fraction of angular particles increases. These results reflect variations in particle mobility, and highlight the relative role of contact stiffness vs. fabric‐changes.

Select this Article		Non‐Grouted Ratio Evaluation of Rock Bolts by Reflection of Guided Ultrasonic Waves Jung‐Doung Yu, Ph.D. Student, Myeong‐Ho Bae, Graduate Student, In‐Mo Lee, Professor, and Jong‐Sub Lee, Associate Professor Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000767 Posted ahead of print 14 May 2012 Full Text: \| Download PDF
	+ -	Show Abstract The objective of this study is to develop and apply reflection methods for guided ultrasonic waves used in evaluating the grout condition of rock bolts installed in a rock mass. Three types of rock bolts with different grouting ratios are prepared. First, piezoelectric disk elements are used as the source of guided ultrasonic waves to investigate grouted non‐embedded rock bolts. Second, reflection methods with piezo disk elements and hammer impacts are employed using rock bolts embedded in concrete columns. Third, a hammer impact with a center punch is applied for investigating rock bolts embedded in a rock mass in the field. The measured guided waves were analyzed using wavelet transforms. The peak magnitudes of the wavelet transform are used for group velocity calculations. While piezo disk elements are sufficient as sources for non‐embedded rock bolts and rock bolts installed in concrete columns, they do not provide sufficient energy in the field. However, a hammer impact with a center punch can generate guided ultrasonic waves with enough energy to evaluate the non‐grouted ratio in rock bolts embedded in a rock mass. The group velocities of the guided ultrasonic waves increase with increasing non‐grouted ratio. This study demonstrates that the suggested hammer impact method is effective for evaluating the non‐grouted ratio of rock bolts in the field.

Select this Article		Bayesian Approach for Probabilistic Site Characterization Using Cone Penetration Tests Zijun Cao and Yu Wang, M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000765 Posted ahead of print 3 May 2012 Full Text: \| Download PDF
	+ -	Show Abstract This paper develops a Bayesian approach for probabilistic site characterization (i.e., on both stratigraphy and soil properties) using cone penetration tests (CPT). The available site information prior to the project (e.g., existing geological maps, geotechnical reports and local experience) is utilized in the Bayesian approach as “prior knowledge”, and it is integrated systematically with results of CPT tests that are performed deliberately for the project. The inherent spatial variability of soil is modeled explicitly by random field theory. The proposed approach contains two major components: a Bayesian model class selection method to identify the most probable number of statistically homogenous layers of soil and a Bayesian system identification method to estimate the most probable layer thicknesses and soil properties probabilistically. Equations are derived for the Bayesian approach, and the proposed approach is illustrated using a set of real CPT data obtained from a site in Netherlands. It has been shown that the proposed approach correctly identifies the number and thicknesses/boundaries of the statistically homogenous layers of soil and provides proper probabilistic characterization of soil properties. The Bayesian approach provides a means to identify the statistically homogenous layers progressively by gradually “zooming” into local differences with improved “resolution”, and it also contains a mechanism to determine when to stop such “zooming”. In addition, a sensitivity study is performed to explore the effect of prior knowledge.

Select this Article		Probabilistic Porous Model to Simulate the Retention Curve of Soils Eduardo Rojas and Jaime Horta Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000763 Posted ahead of print 3 May 2012 Full Text: \| Download PDF
	+ -	Show Abstract A probabilistic porous model is used to simulate the retention curves of different types of soils. The model is based on the same principles of porous networks models however it shows important advantages over them. It considers two different elements: the sites and the bonds. It is able to simulate the retention curves of a material when its pore size distribution is known. It can also be used to interpret more realistically the results of mercury intrusion porosimetry tests. In this paper the model is used to obtain the pore size distribution of different soils using the retention curve as its data source. The comparison between numerical and experimental results for different soils shows that the model approximately reproduces the pore size distribution obtained from mercury intrusion porosimetry tests.

Select this Article		System Reliability of Concrete Dams with Respect to Foundation Stability — Application to a Spillway Marie Westberg and Fredrik Johansson Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000761 Posted ahead of print 2 May 2012 Full Text: \| Download PDF
	+ -	Show Abstract Structural reliability analysis is not widely used for the design and assessment of concrete dams. In this paper, the system reliability of a spillway structure consisting of two monoliths is calculated. Limit state functions are defined from the failure modes sliding in the concrete rock contact, sliding in the rock mass and adjusted overturning. Random variables in the limit state functions are defined by stochastic distributions. These are defined based on site investigations and laboratory tests from samples taken at the dam. Simulations and information from literature is used for the remaining variables. The safety index is calculated by FORM for each failure mode and monolith, and the system reliability is approximated by direct integration of the bivariate normal distribution. The output is the safety index including associated sensitivity values at the single failure mode, monolith and system levels. The results show that the system safety is governed by a persistent rock joint beneath one monolith. A system reliability analysis is found to be a useful tool in the dam risk management process as it can be used to calculate the probability of failure and to identify important failure modes and variables.

Select this Article		Pile‐Group Response to Large Soil Displacements and Liquefaction: Centrifuge Experiments versus a Physically Simplified Analysis P. Tasiopoulou, N. Gerolymos, T. Tazoh, and G. Gazetas Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000759 Posted ahead of print 28 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract The paper presents a physically simplified method for computing displacements and structural forces on piles under conditions of lateral spreading triggered by the large seaward displacement of a harbor quay‐wall. The method avoids the empirical selection of stiffness‐reduction factors and the associated use of p ‐ y curves that current state‐of‐the‐art methods employ. Instead, the 3D highly nonlinear problem is approximated in two steps, both involving 2D plane‐strain analyses. The first step involves a vertical (representative) slice in which the pile group has been omitted and which, shaken at its base, gives the permanent deformation of the quay‐wall and of the liquefiable soil. It is an effective stress analysis. In the second step, a horizontal (representative) slice taken from the middle of the liquefiable zone is subjected to an outward quay‐wall displacement; the goal is to evaluate the reduction of the pile displacement over the free‐field one, and the ensuing pile group distress. The pile resistance to ground deformation depends heavily on the constraints imposed by the superstructure, as well on the exact stiffness of the soil layers. Thus, the interplay between soil‐piles‐quaywall under soil flow conditions is captured in a physically meaningful way. The predictions compare well with results from two centrifuge tests.

Select this Article		Effects of Geocell Confinement on Strength and Deformation Behavior of Gravel Ben Leshchinsky and Hoe Ling, M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000757 Posted ahead of print 26 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract In past years, railroad transportation has been of growing interest due to its efficiency and advancement in railway technologies. However, many issues arise due to the variability in subsurface conditions along the sizeable lengths of track that exist. One very important issue is the need for significant upkeep and maintenance for railways passing over areas of poor soil conditions due to continuous deformation and a lack of stiffness from the foundation. One general solution for lack of substructure integrity has been confinement, applied through a variety of reinforcement types, including geocell. To investigate the effectiveness of geocell confinement on substructure integrity, a series of embankment model tests with different configurations of geocell placement (one layer and two layers of geocell) were constructed and loaded monotonically and cyclically for comparison to unreinforced, control tests. Upon the completion of these tests, the model embankments were simulated numerically using Finite Element procedures. The results, which matched reasonably well, were then used as validation for a parametric study, observing the effects of less competent geocell material, gravel and foundation conditions and their implications. The tests and numerical simulations demonstrate that geocell confinement effectively increased stiffness and strength of a gravel embankment, while reducing vertical settlement and lateral spreading. Additionally, the parametric study shows that the use of geocell provides a composite, “mattressing” effect that distributes subgrade stress more uniformly than without reinforcement, increasing bearing capacity and reducing settlement, especially on soft foundations. The results suggested that in some site conditions, use of geocell might be an economical alternative to frequent maintenance and/or lower train speeds.

Select this Article		Behavior of Coarse Widely Graded Soils under Low Confining Pressures H. F. Zhao, L. M. Zhang, F. ASCE, and D. S. Chang, S. M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000755 Posted ahead of print 25 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract Colluvial soils are usually coarse and widely graded. Shallow‐seated failures occur frequently in colluvial soil deposits during rainfall infiltration. This paper aims to investigate the behavior of coarse widely graded soils under very low confining pressures of 5–25 kPa encountered in shallow‐seated failures. Isotropic consolidation tests, drained triaxial tests, and undrained triaxial tests were conducted on several widely graded soils with different coarse contents but the same void ratio of 0.62. With increasing coarse content, the soil microstructure changes from a fines‐controlled structure to a coarse‐controlled structure after a critical coarse content of approximately 70%. Silty sand with gravel with a coarse content close to the critical value exhibits the highest compressibility due to the presence of large inter‐aggregate pores. Even under very low confining pressures, such soil still shows strong contractive behavior during drained loading, and generates large positive pore‐water pressures during undrained loading. This explains why shallow‐seated failures occur frequently in colluvial soil deposits due to rainfall infiltration. Soils with lower or higher coarse contents than the critical value may show dilative behavior under the same low confining pressures. The critical state friction angle increases with the coarse content.

Select this Article		Pile Setup in Cohesive Soil: Analytical Quantifications and Design Recommendations K. W. Ng, M. T. Suleiman, and S. Sritharan Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000753 Posted ahead of print 25 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract This paper establishes a methodology to quantify pile setup by using recent field test data that was presented in a companion paper for steel H‐piles driven in cohesive soils. Existing methods found in literature for the same purpose either require restrikes of piles onsite, or are developed for a specific soil type and seldom use easily quantifiable soil properties despite their significant influence on pile setup. Following a critical evaluation of the existing methods, a new approach for estimating pile setup was developed using dynamic measurements and analyses in combination with measured soil properties, such as the horizontal coefficient of consolidation, undrained shear strength and/or Standard Penetration Test N‐value. Using pile setup information available in literature, the proposed approach has shown that it provides good estimates for the setup of steel H‐piles, as well as for other types and sizes of driven piles.

Select this Article		Pile Setup in Cohesive Soil: An Experimental Investigation K. W. Ng, M. Roling, S. S. AbdelSalam, M. T. Suleiman, and S. Sritharan Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000751 Posted ahead of print 25 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract Pile setup in cohesive soils has been a known phenomenon for several decades. However, a systematic field investigation to provide the needed data to develop analytical procedures and integrate pile setup into the design method rarely exists. This paper summarizes a recently completed field investigation on five fully instrumented steel H‐piles embedded in cohesive soils, while a companion paper discusses the development of the pile setup method. During the field investigation detailed soil characterization, monitoring of soil total lateral stress and pore water pressure, collection of pile dynamic restrike data as a function of time, and vertical static load tests were completed. Restrike measurements confirm that pile setup occurs at a logarithmic rate following the end of driving, and its development correlates well with the rate of dissipation of the measured pore water pressure. Based on the field data collected it was concluded that the skin friction component, not the end bearing, contributes predominantly to the setup, which can be accurately estimated for practical purposes using soil properties, such as coefficient of consolidation, undrained shear strength and/or SPT N‐value.

Select this Article		Shaft Capacity of Displacement Piles in Clay Using the CPT Barry M. Lehane, Yunong Li, and Ryan Williams Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000749 Posted ahead of print 25 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract The prediction of the shaft capacity of displacement piles in clay still relies wholly on empirical or semi‐empirical approaches. This paper examines the predictive abilities of five well known methods against an extended version of the database of pile tests compiled by Chow (1997). It is seen that coefficients of variation of the ratio of calculated to measured capacities (Q_c/Q_m) are significantly higher than expected. The paper then employs the database of shaft capacities to examine potential relationships between local shaft friction and the CPT end resistance (q_t). Predictions are subsequently compared with capacities measured in a series of centrifuge tests and with the distributions of peak frictions observed in two well documented field tests. Widely different formulations adopted by each of the existing empirical methods give broadly similar COV values for Q_c/Q_m ratios and it is concluded that the database of high quality pile tests needs to be expanded significantly if the reliability of estimates of shaft capacity in clay is to be improved.

Select this Article		Bearing Capacity of Spread Footings on Aggregate Pier Reinforced Clay Armin W. Stuedlein, Ph.D., P.E., M. ASCE and Robert D. Holtz, Ph.D., P.E., D.GE, Dist. M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000748 Posted ahead of print 18 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract Aggregate piers, also known as stone columns, are a commonly used ground improvement technique to stiffen existing soils for the support of structure foundations. This paper presents an evaluation of existing analytical expressions for the bearing capacity of spread footings supported on aggregate pier reinforced clay. The accuracy of these models was investigated using a database of high‐quality footing load test data. The existing models were compared using the bias (i.e., the ratio of measured and calculated bearing capacity), and they produced a wide range in predicted bearing capacities. Selected analytical models were empirically modified using the load test database, and this resulted in improved accuracy and reduced variability. Back‐calculated aggregate pier bearing capacity and cavity expansion factors are shown to be inversely proportional to undrained shear strength and therefore to the ultimate confining pressure available at failure. This finding is attributed to the curved failure envelope of the angular aggregate used in pier construction. Additionally, a multiple non‐linear regression model suitable for spread footings resting on aggregate piers under a wide range of pier configurations is presented. The regression model is shown to produce more accurate bearing capacity estimates than existing analytical models.

Select this Article		Improvement of Hole Erosion Test and Results on Reference Soils Iman Haghighi, Christophe Chevalier, Myriam Duc, Sylvine Guédon, and Philippe Reiffsteck Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000747 Posted ahead of print 18 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract Understanding the factors that control the transport of soil particles detached by water is essential to predict the contingency of internal and surface erosion of embankments during storms and floods. It is particularly useful to be able to evaluate the sensitivity of the available soils to erosion at an early stage of a project and the risk assessment of an existing earthwork. The presented study based on laboratory tests with Hole Erosion Test apparatus (HET) tries to characterize internal erosion of soils. The test consists of eroding a drilled soil specimen by water flow with a constant pressure drop at the boundaries of the specimen recording the flow rate and study the hole enlargement. A new version of the apparatus with improved instruments and interpretation method is proposed estimating the erosion rate based on the turbidity of the outflow and independent of hydraulic charge. Several remolded kaolinite‐sand mixtures been tested as reference soil textures and the results are analyzed with the proposed and the existing interpretation methods.

Select this Article		Field Tests, Modification and Application of Deep Soil Mixing (DSM) Method in Soft Clay Jin‐Jian Chen, Lianyang Zhang, P.E., M. ASCE, Jun‐Feng Zhang, Yan‐Fei Zhu, and Jian‐Hua Wang Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000746 Posted ahead of print 18 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract The installation of soil‐cement columns causes excess pore‐water pressures and movements of surrounding ground, which impact adjacent underground structures. In Shanghai, a triple‐shaft deep soil mixing (DSM) method has been proposed and is widely used in order to minimize the installation effects. But when this DSM method was used to install soil‐cement columns close to a Metro tunnel, unacceptable soil displacement was caused even at the very beginning. So it was decided to conduct field tests in order to investigate the effect of major factors affecting the impact of DSM installations and then modify the construction parameters so that the soil displacement due to the DSM construction would not exceed the allowable limit. The field tests consist of two phases: Phase I tests on single DSM column installations close to the Metro tunnel to modify the construction parameters and Phase II tests on continuous multiple DSM column installations far from the Metro tunnel to validate the modified construction parameters. Detailed pore water pressure and soil displacement measurements were conducted during the field tests. Based on the field tests, the traditional DSM method was modified by using higher water cement ratio, lower mixing speed, and no injection during withdrawal and adopting a new installation sequence for continuous construction that starts from the farthest row and gets closer to the tunnel. Using the modified construction parameters, the triple‐shaft DSM method was successfully applied in the large‐scale soil improvement of an underground highway excavation project close to the Metro tunnels. This paper describes the background, the field tests, the modified DSM method and its successful application.

Select this Article		Mobilization of Reinforcement Forces in Fiber‐Reinforced Soil Chunling Li, M. ASCE and Jorge G. Zornberg, M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000745 Posted ahead of print 13 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract Fiber reinforcement represents a promising alternative in projects involving localized repair of slopes and reinforcement of thin soil veneers, where planar reinforcement (e.g, with geotextiles, geogrids) is difficult to implement. Current design methodologies allow quantification of the shear strength of fiber‐soil composite in terms of parameters that independently characterize the soil matrix and fibers. The shear strength of fiber reinforced soil is considered to have two components, including the shear strength of soil matrix and the tension mobilized within fibers. Triaxial compression tests and fiber pullout tests were conducted to evaluate how the fiber tension is mobilized for varying shear strain levels. The results of this evaluation provide insights into whether the shear strength of fiber‐reinforced soil is governed by peak or residual shear strength of unreinforced soil. A revision to existing design methodology is proposed in which the individual contribution of fibers and soil matrix is quantified based on strain level. The appropriateness of using the peak or residual shear strength of the unreinforced soil for predicting the ‘equivalent’ shear strength of fiber‐soil composite is discussed based on strain compatibility considerations.

Select this Article		Quantification of Model Uncertainty in Shear Strength Predictions for Fiber‐Reinforced Sand Shadi S. Najjar, A. M. ASCE, Salah Sadek, M. ASCE, and Alexander Alcovero Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000742 Posted ahead of print 12 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract Several models have been suggested to estimate the improvement brought by fibers to the shear strength of fiber‐reinforced sands. To date the effectiveness and reliability of these models have not been the subject of a comprehensive evaluation. The objectives of this paper are to (1) compile the experimental data available in the literature on the behavior of fiber‐reinforced sands into a comprehensive state‐of‐the‐art database, (2) quantify the model uncertainty and bias of current strength prediction models for fiber‐reinforced sands and (3) provide insight regarding possible modifications that could be made to the formulation of available models to improve their predictive effectiveness and reduce their model uncertainty. Two models which are considered to present the best available approaches to predicting sand‐fiber shear strength were evaluated: the “energy‐based” model and the “discrete” model. The energy‐based model was found to underestimate the measured friction coefficient on average by about 10%, while the discrete model overestimated the friction coefficient by 6%, with associated coefficients of variation on bias values of 0.20 and 0.17, respectively. With the introduction of minor modifications to these models, the average bias error was eliminated and the coefficients of variation in the ratio of predicted to measured shear strength (bias) were reduced to 0.17 and 0.12, respectively for the two models.

Select this Article		Field Hydrology of Landfill Final Covers with Composite Barrier Layers William H. Albright, Craig H. Benson, and Preecha Apiwantragoon Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000741 Posted ahead of print 11 April 2012 Full Text: \| Download PDF
	+ -	Show Abstract A study was conducted at seven sites across the US to evaluate the field hydrology of final covers with a composite barrier (geomembrane over a soil barrier or a geosynthetic clay liner) for final closure of landfills. The water balance of each cover was monitored with a large (10 m × 20 m) instrumented drainage lysimeter. With one exception, the covers limited average annual percolation to < 2.8 mm/yr (< 0.4% of precipitation). The geomembrane barrier at one site (Marina, CA) was likely damaged during construction; percolation at this site averaged 30 mm/yr (6.9% of precipitation). Annual percolation through the cover at the wettest site (Cedar Rapids, IA) ranged between 0.1 and 6.2 mm/yr. Annual percolation at arid and semi‐arid sites was typically no more than a trace (< 0.1 mm/yr). Percolation from all test covers generally was coincident with high water storage in the surface soil layer and lateral flow in the drainage layer on the surface of the geomembrane barrier. Water balance predictions were made with the HELP model using site‐specific inputs. Surface runoff was over‐predicted and evapotranspiration under‐predicted when as‐built soil hydraulic properties were used as input. Better agreement was obtained when in‐service soil hydraulic properties were used as input. Lateral flow was consistently over‐predicted regardless of hydraulic properties, and no correspondence existed between predicted and measured percolation.

Select this Article		Probabilistic Seismic Hazard Analysis for Maximum Seismic Shear Stresses in Soils Using Improved Ground Motion Parameters Tadahiro Kishida, A. M. ASCE and Chi‐Chin Tsai, M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000740 Posted ahead of print 31 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract Maximum seismic shear stresses (τ_max) have been recognized as one of the important parameters in design practice. This study develops ground motion parameters for τ_max and implements these in probabilistic seismic hazard analysis (PSHA) to provide the τ_max distribution of deep soil layers for design purposes. The application of the improved ground motion parameters for τ_max is demonstrated at the Oakland International Airport, where thick Young Bay Mud deposit exists under the artificial fill. Model biases in the predictive equations of seismic shear stress reduction coefficients (r_d) are evaluated by comparison to the site response analysis results performed with a wide range of input ground motions. On the basis of these results, we introduce improved ground motion parameters for τ_max (I_tau) as a linear combination of spectral accelerations and implemented in PSHA to calculate seismic hazard curves. Conditional mean spectra are calculated given I_tau at 10% in 50 years to illustrate the variations in frequency contents with depth compared with Uniform Hazard Spectra (UHS). Finally, τ_max is calculated with depth given hazard values of I_tau and compared with the peak ground acceleration (PGA)‐based and UHS‐based calculations. Analysis results show that τ_max will be underestimated for deep soil layers by PGA‐based calculation if the median value of r_d is used in design practice.

Select this Article		Uplift Behavior of Vertical Piles Embedded in Oil‐Contaminated Sand Ahmed M. A. Nasr Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000739 Posted ahead of print 29 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract There are several problems dealing with oil‐contaminated soil which affect environmental quality and alter the geotechnical properties of the soil. The influence of oil‐contamination on the uplift performance of model concrete piles embedded in sand at various densities is investigated. In this study the model parameters are varied to include the thickness and diameter of contaminated layer, type of oil contamination, pile surface roughness, and pile installation method. Contaminated sand layers were prepared by mixing the sand with an oil content of 0–3% with respect to dry soil to match the field conditions. The results were then analyzed to study the effect of each parameter. To evaluate the scale effects, two sizes of model piles were tested and the results were compared. This paper also discussed the effect of oil contamination on the relative ground movement around the pile surface. The results indicated that the uplift resistance was drastically reduced by oil contamination. The maximum reduction in uplift resistance and skin friction factor occurred at low contamination (oil content = 1%). Initial sand density and method of pile installation are significant factors affecting uplift capacity of pile embedded in oil‐contaminated sand. The experimental results were used for the development of linear regression equations. These equations relate the uplift capacity ratio for piles embedded in contaminated sand to the aforementioned parameters.

Select this Article		Long Term Lateral Cyclic Response of Suction Caisson Foundations in Sand B. Zhu, B. W. Byrne, and G. T. Houlsby Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000738 Posted ahead of print 26 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract Skirted gravity base foundations and suction caisson foundations are considered as viable alternatives to monopile foundations for offshore wind turbines. Whilst recent work (e.g. Villalobos et al., 2009) has focused on the monotonic moment‐rotation response for shallow foundations, the cyclic response and the accumulation of rotation over the life of the turbine must also be addressed. This paper presents cyclic loading tests where approximately 10,000 cycles, with different loading characteristics, were applied to a model shallow foundation (a caisson) in loose sand. On the basis of these tests a framework for assessing the accumulated angular rotation due to cycling was developed. The settlement and cyclic stiffness response of the caisson are also assessed. It was found, not unexpectedly, that the accumulated settlement of the caisson increased with number of cycles and cyclic amplitude. It was also found that a cyclic loading regime intermediate between one‐way and full two‐way cycling produced the largest rotations. The cyclic stiffness was relatively unaffected by the number of cycles. Using an appropriate scaling technique, the proposed framework has been used to predict the long‐term accumulated angular rotation for an example field‐scale mono‐caisson structure.

Select this Article		Evaluation on Failure of Fiber‐Reinforced Sand Zhiwei Gao and Jidong Zhao Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000737 Posted ahead of print 22 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract Fiber reinforcement can help to enhance soil strength, stabilize near surface soil layers and mitigate the risk of soil liquefaction. Evaluation of the strength of fiber‐reinforced soils needs a proper failure criterion. This study presents a three‐dimensional failure criterion for fiber‐reinforced sand. By assuming that the total strength of composite is a combination of the shear resistance of the host soil and the reinforcement of fibers, a general anisotropic failure criterion is proposed with special emphasis on the effect of isotropically/anisotropically distributed fibers. An anisotropic variable, defined by the joint invariant of the deviatoric stress tensor and a deviatoric fiber distribution tensor, is introduced in the criterion to quantify the fiber orientation with respect to the strain rate/stress direction at failure. With further consideration of fiber concentration and aspect ratio, the proposed criterion is applied to predicting the failure of fiber‐reinforced sand under conventional triaxial compression/extension tests, for both isotropically and orientated distributed fiber cases. The predictions are in good agreement with test results available in the literature. Practical significance of using this criterion for such problems as inclined slope stabilization is briefly discussed.

Select this Article		Effect of Uniformity Coefficient on G/G_max and Damping Ratio of Uniform to Well Graded Quartz Sands T. Wichtmann and T. Triantafyllidis Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000735 Posted ahead of print 22 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract The modulus degradation curves G(γ)/G_max and the damping ratio D(γ) of 27 clean quartz sands with specially mixed grain size distribution curves were measured in approximately 280 resonant column tests. For each material, tests with different pressures and densities were performed. Based on the test data it is demonstrated that the shear modulus degradation is larger for higher values of the uniformity coefficient, C_u = d₆₀/d₁₀, while it is rather independent of the mean grain size, d₅₀. The observed C_u‐dependence of the curves G(γ)/G_max is not adequately described by common empirical equations, because theses equations were developed based on tests on uniform granular materials. In order to consider the influence of the uniformity coefficient, the paper proposes correlations of the parameters of the common empirical equations with C_u. Good agreement between the prediction of the extended empirical equations and experimental data collected from the literature is demonstrated. Furthermore, the test data reveal that the curves of damping ratio, D(γ), and the threshold shear strain amplitude indicating the onset of residual deformation accumulation, γ_tv, are rather independent of d₅₀ and C_u. The threshold shear strain amplitude at the onset of modulus degradation, γ_tl, slightly decreases with increasing values of d₅₀ and C_u.

Select this Article		Bootstrapping for Characterizing the Effect of Uncertainty in Sample Statistics for Braced Excavations Zhe Luo, Sez Atamturktur, M. ASCE, and C. Hsein Juang, F. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000734 Posted ahead of print 21 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract A simple procedure for assessing the probability of serviceability failure in a braced excavation involving bootstrapping to characterize the effect of uncertainty in sample statistics is presented. Here, the failure is defined when an excavation system's response, in terms of the maximum wall deflection or ground settlement, exceeds the limiting value specified by the client or in an applicable code. The analysis for the probability of failure (or probability of exceedance in this paper) necessitates an evaluation of the means and standard deviations of critical soil parameters. In geotechnical practice, these means and standard deviations are often estimated from a very limited data set, which can lead to uncertainty in the derived sample statistics. Thus, in this study bootstrapping is used to characterize the uncertainty or variation of sample statistics and its effect on the failure probability. Through the bootstrapping analysis, the probability of exceedance can be presented as a confidence interval instead of a single, fixed probability. The information gained should enable the engineer to make a more rational assessment of the risk of serviceability failure in a braced excavation. The study points to the potential of bootstrap method in coping with the problem of having to evaluate failure probability with uncertain sample statistics.

Select this Article		Comparison of Rapid Load Test Analysis Techniques in Clay Soils Michael J. Brown and John J. M. Powell Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000733 Posted ahead of print 21 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract Rapid load pile testing (RLT) techniques such as Statnamic were developed as an alternative to more frequently adopted static and dynamic tests. The existing unloading point method (UPM) for deriving equivalent static load‐settlement behaviour from rapid load tests seems to be adequate in coarse grained soils but may result in poor prediction in clays and silts. In order to address these shortcomings the UPM method has been improved to reflect soil type and new analysis techniques have been developed. In order to test the performance of the improved UPM and new analysis techniques pile tests from two clay sites were analysed. The first case study site was underlain by very to extremely high plasticity Quaternary London Clay and the second site by low to intermediate plasticity matrix dominant glacial till. The best predictions of static equivalent load‐settlement behaviour for very high plasticity clay were obtained from a new analysis technique that incorporated a soil specific rate effect parameter (selected based upon the clays plasticity index) that varied with pile settlement. In general the UPM performed better for tests undertaken in the low to intermediate plasticity glacial till as there is greater experience of RLT in these soils. The results of the study suggest that the development of analysis techniques would benefit greatly from tests in a wider variety of soil types. Based upon the findings of this study improvements to the UPM and Schmuker techniques are presented which include pile‐settlement dependant variation of the damping or rate effect parameters.

Select this Article		Use of Vacuum for the Stabilization of Dry Sand Slopes B. Bate, A. M. ASCE and L. M. Zhang, M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000731 Posted ahead of print 15 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract Vacuum is proposed as a means for rescuing soil slopes showing signs of impending failure. Two aspects associated with the proposed method were studied; namely, the theory of airflow through dry soils and the effectiveness of vacuum for enhancing the stability of soil slopes. A model test device was developed, and two series of tests were carried out using this device. One was a series of tests on pore‐air pressure distributions in dry sand slopes and the second series involved dry sand slope stability tests. The results revealed that a vacuum (negative pore‐air pressure) even as small as −0.4 kPa significantly increased the stability of the model slopes with dimensions of 0.9 × 0.5 × 0.28 m (length × width × height). The pore‐air pressure distributions in the model slopes were simulated using a finite element partial differential equation solver, FlexPDE. Fick's law and mass conservation were used to formulate the airflow through dry soils. Good agreement was achieved between the experiment results and the numerical simulations. A computer routine, called Slope‐Air, was developed for slope stability analysis using Bishop's simplified method and considering the pore‐air pressure distributions in the slope. The calculated factors of safety of the model slopes at failure were consistent with the results of the model slope stability tests.

Select this Article		Oil‐Operated Fixed‐Piston Sampler and Its Applicability S. G. Chung and H. J. Kweon Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000730 Posted ahead of print 15 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract The current paper presents the development of an oil‐operated fixed‐piston sampler. This sampler includes a vacuum breaker that prevents the suction between the sample and the piston during disassembly and an improved version of a complex system used for continuous advancement in mechanical samplers. The improvement makes the new sampler easy to operate similar to the hydraulic sampler. The oil‐operated and hydraulic samplers were used at a site in the Nakdong River delta. Suction, shear wave velocity, and consolidation tests were performed on 100 mm‐long specimens equally divided by the extruded samples, as well as the seismic flat dilatometer and the piezocone tests in the field. The results show that the new sampler gave better sample quality than the hydraulic‐type sampler, indicating better recovery ratio. The main difference in sample quality between the two samplers can be attributed to mechanical destructuration, owing to the stepped advancement and the slight tilt of the hydraulic sampler.

Select this Article		Influence of Spatially Variable Side Friction and Collocated Data on Single and Multiple Shaft Resistances Harald Klammler, Michael McVay, Peter Lai, and David Horhota Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000728 Posted ahead of print 14 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract Reliability based design such as load and resistance factor design (LRFD) aims at meeting desired probability of failure levels for engineered structures. The present work attempts to contribute to this field by analyzing the influence of spatially variable soil /rock strength on the axial resistance uncertainty of single and multiple shafts in group layouts. This includes spatial variability over the individual shaft surfaces, effects of limited data, random measurement errors and workmanship. Possible correlation between boring data inside or near the footprint of a foundation and the foundation itself are considered. In a geostatistical approach spatial averaging (up‐scaling) and a degenerate case of ordinary kriging are applied to develop variance reduction charts and design equations for a series of foundation group layouts (single, double, triple and quadruple). For the potential situation of an unknown horizontal correlation range at a site, the worst case scenarios are identified and demonstrated in an example problem. Resulting probabilities of failure are applied to the whole foundation (i.e., group) rather than for single objects. It is found that a boring at the center of a group footprint can significantly reduce resistance prediction uncertainty, especially under the worst case scenario for unknown horizontal correlation range. In contrast, independent of the presence of a center boring or not, the uncertainty reduction through additional borings becomes small, once four or five borings are available.

Select this Article		Design Methodology for Axially Loaded Auger Cast‐In‐Place (ACIP) and Drilled Displacement (DD) Piles Sungwon Park, Lance A. Roberts, M. ASCE, and Anil Misra, M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000727 Posted ahead of print 14 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract With the increasing use of augered cast‐in‐place (ACIP) and drilled displacement (DD) piles in new construction, it is important that proper design parameters be incorporated when evaluating pile performance using reliability‐based design (RBD) methods. Although augered piles can be distinguished from bored piles, including drilled shafts, and driven piles by the magnitude of effective stress changes they produce in the vicinity of the pile during construction, the current design methods for augered piles generally use the same design methods as those used for bored or driven piles. To enhance the efficiency of the augered piles, a unique design method must be developed. This paper focuses upon developing a design methodology for axially loaded augered piles installed in predominately sandy soils using the t–z method. To develop the design parameters for augered piles, back‐calculation of the t–z parameters was conducted using static load‐test data. The data from 17 static pile load‐tests conducted on augered piles from construction sites were obtained. Load‐settlement and load transfer curves fittings were performed using the t–z model to back‐calculate a set of soil‐pile interfacial and tip parameters, along with their variability. Correlation of the back‐calculated t–z model parameters with the standard field investigation data was conducted and the most promising correlations were incorporated into the t–z model based design methodology. Subsequently, the t–z method for augered pile design was evaluated by comparing the predicted and measured load‐settlement and load transfer curves. In addition, the t–z method was used to perform probabilistic load‐settlement analyses and obtain resistance factors applicable to the Load and Resistance Factor Design (LRFD) approach.

Select this Article		A Simple Model for Nonlinear Response of Fifty‐Two Laterally Loaded Piles Wei Dong Guo, M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000726 Posted ahead of print 8 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract Response of a laterally loaded pile is normally dominated by limiting force per unit length (LFP, p_u) mobilised along the pile to a depth of plastic zone (e.g. maximum slip depth, max x_p), and depends on pile‐soil relative rigidity (via subgrade modulus of elasticity k). The values of the p_u and the shear modulus (G, thus k) were deduced extensively against measured response of thirty‐two and twenty piles tested in‐situ in clay and sand, respectively. In this paper, simplified closed‐form solutions are presented to design laterally loaded piles. The parameters of the p_u and the G gained previously are utilised to examine the impact of loading eccentricity on piles, and to assess the validity of existing p_u profiles. Expressions are also explored and provided regarding determinations of the p_u profiles, the modulus of subgrade reaction k (via G); the ranges of plastic zone (max x_p), and depth of elastic influence (via critical pile length L_cr), along with the correlations between shear modulus of soil G and undrained shear strength (s_u) and/or SPT blow count (N). It is noted that the popularly adopted LFPs (such as Matlock's LFP, Reese's LFP or API code methods) are not sufficiently accurate for 60∼85% of the fifty‐two piles investigated herein, especially for those with a diameter >1.5 m.

Select this Article		Tunnel Reinforcement by Using Pressure‐Induced Inflatable Pipes Method Jeong‐Jun Park, In‐Sung Cho, In‐Mo Lee, and Seok‐Won Lee Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000725 Posted ahead of print 7 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract A new tunnel auxiliary method, the pressure‐induced inflatable pipes method, is proposed in this paper. It utilizes the concept of cavity expansion for tunnel reinforcement by forming an umbrella arch on the roof of the tunnel. When each inflatable pipe is inserted and expanded by pressure in the boreholes of the umbrella arch, the ground around the borehole can be compacted so that the stress conditions above the tunnel perimeter are changed favorably. To verify the reinforcement effect of this new concept, a pilot‐scale chamber test, numerical analysis, and trapdoor test were performed and compared. In the pilot‐scale chamber test, three types of inflatable pipes were tested to check their capability for expansion and each type of pipe was demonstrate to function correctly by expanding only in the intended direction. Numerical analysis of a tunnel and trapdoor tests applied with the inflatable pipes were also performed to determine the reinforcement effects of the proposed technique. The results imply that the new method with three‐directional inflatable pipe can contribute to reducing tunnel convergence and face settlement.

Select this Article		Geotechnical Characterization and Random Field Modeling of Desiccated Clay Armin W. Stuedlein, Ph.D., P.E. M. ASCE, Steven L. Kramer, Ph.D., P.E., M. ASCE, Pedro Arduino, Ph.D., M. ASCE, and Robert. D. Holtz, Ph.D., P.E., D.GE, Dist. M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000723 Posted ahead of print 3 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract An extensive set of in‐situ and laboratory test data are presented for a footing load test site east of Houston, Texas, in desiccated Beaumont Clay. The in‐situ test program included standard and cone penetration tests (SPT and CPT, respectively), the latter of which was selected for statistical analysis to produce vertical and horizontal random field model parameters for corrected cone tip resistance. Given the relatively high sampling frequency of cone tip resistance in the vertical direction, the vertical random field model parameters were determined using the modified Bartlett's test statistic with fitted autocorrelation models subject to a strict fitting criterion. Horizontal random field model parameters were generated by collapsing the 2D distribution of the CPTs to a 1D representation and using less stringent evaluation of autocorrelation. The results of this study indicate that Beaumont clay exhibits greater inherent spatial variability than previously reported at other clay sites which is attributed to the secondary structure of desiccated clay. A companion paper discusses the performance of a footing load test in the context of spatial and transformation uncertainty.

Select this Article		Investigation of Geotechnical Parameters Affecting Electrical Resistivity of Compacted Clays G. Kibria and M. S. Hossain Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000722 Posted ahead of print 1 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract The use of resistivity imaging (RI) in subsurface investigation has increased in recent years. RI is a non‐ destructive method and provides a continuous image of the subsurface. However, only qualitative evaluation of the subsurface can be obtained from RI. The correlations between RI results and geotechnical engineering properties of soils have become important for site investigation using this method. The primary objective of the current study was to determine the geotechnical parameters affecting electrical resistivity of compacted clays. Understanding the influential factors will be helpful in determining the correlations between RI results and geotechnical properties of soil. The effects of moisture content, unit weight, degree of saturation, specific surface area, percentages of pores and ion composition on soil resistivity were investigated. Soil samples used in the study were classified as highly plastic clay (CH) according to the Unified Soil Classification System (USCS). High energy X‐Ray fluorescence (XRF) tests indicated the presence of high percentages of aluminum, silicon and calcium ions in the samples. In addition, scanning electron microscope (SEM) images were analyzed to identify clay structure and the distribution of pores. It was determined that the dominant clay mineral in the soil samples was montmorillonite. Soil resistivity tests were conducted in the laboratory at varying moisture contents and unit weights. Based on the experimental results, it was observed that the average reduction in soil resistivity was 13.8 Ohm‐m for an increase of moisture content from 10% to 20%. Test results indicated that soil resistivity decreased with the increase in moist unit weight. In addition, soil resistivity increased from 4.3 to 14.2 Ohm‐m for an increase of surface area from 69.6 to 107.1 m²/gm at 18% moisture content and 11.8 kN/m³ dry unit weight. Soil with high surface area required more water for the formation of water film and bridging between the particles. This might cause an increase in soil resistivity with an increase of surface area. Moreover, specific surface area also controlled resistivity when soil resistivity was plotted against calcium ions and pore spaces of the soil samples. Therefore, in addition to moisture content and unit weight, specific surface area of soils was identified as an important factor influencing soil resistivity.

Select this Article		Simple Wave Solution for Seismic Earth Pressures on Non‐Yielding Walls Panos Kloukinas, Miltiadis Langousis, M. ASCE, and George Mylonakis, M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000721 Posted ahead of print 1 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract Design of retaining walls for earthquake action is traditionally performed by limit analysis procedures — notably the classical solution of Mononobe—Okabe and its variants. Fundamental assumptions of these methods are: (1) the static nature of seismic excitation, (2) the compliance in sliding and/or rocking of the base of the wall, (3) the shear failure of the backfill and the soil‐wall interface, (4) the pre‐specified point of application of soil thrust. Given the restrictive nature of these assumptions, alternative solutions based on wave‐propagation theory have been developed, which do not require failure of the backfill and, thereby, are applicable to non‐yielding walls. Because of the complex mathematics involved, the use of these solutions in practice appears to be limited. A special integration technique inspired from the seminal work of Vlasov and Leontiev is presented, which simplifies the analysis providing closed‐form solutions suitable for practical use.

Select this Article		Pasternak Model for Oblique Pullout of Inextensible Reinforcement S. Patra and J. T. Shahu Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000720 Posted ahead of print 1 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract An analysis is presented for evaluation of pullout capacity of sheet reinforcement subjected to oblique pullout force considering that the subgrade soil is represented as a two‐parameter linear elastic Pasternak model and the reinforcement as inextensible. Use of Pasternak model makes the oblique pullout analysis more realistic. The orientation of the reinforcement at the pullout end is found to be different than the direction of the pullout force and depends on the shear modulus of the subgrade soil. A parametric study is carried out to evaluate the effect of various factors, such as modulus of subgrade reaction, shear modulus of subgrade, angle of interface shear resistance and the obliquity of the pullout force on the magnitude and direction of the reinforcement force and the end‐displacement. For the first time, oblique pullout results have been compared with direct measurements of the reinforcement inclination in the vicinity of the failure surface available in the literature and the experimental data compares well with the present analysis. Model tests on single and multiple sections of sheet and strip reinforcements are also performed to study the suitability and applicability of the present analysis in the design of reinforced soil walls.

Select this Article		Analysis of Foundations Reinforced with Jet Grouting Giuseppe Modoni and Joanna Bzòwka Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000718 Posted ahead of print 1 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract The use of jet grouting columns to increase the bearing capacity and reduce the settlements of foundations is dealt with the aim of formulating a complete design procedure where theoretical analyses and site observations are combined. The study is based on experimental results reported in the literature which show that jet grouting columns are able to transfer high vertical loads to the surrounding soil but also that structural collapse may locally occur due to sudden narrowing of their cross sections and/or to poor soil cementation. Noticeable attention has been then given to these aspects by interpreting the results of full scale tests specifically performed to investigate the characteristics of jet grouting columns and their mechanical interaction with the surrounding soil. The results of this analysis form the basis of a numerical method developed to simulate the response of vertically loaded rafts supported by arrays of columns. The non linear load settlement response of axially loaded columns is modelled with the load transfer curves method customised to account for the irregular shape of jet grouting columns. Extension of the analysis to the whole reinforced foundation is accomplished by considering the mutual interaction between the columns and the upper concrete raft. The variation of column properties is statistically evaluated from the results of field trials, simulated with probabilistic models and introduced into the calculation with a Monte Carlo simulation technique. The main advantages of the proposed method is that the design limit load of the foundation can be expressed in terms of accepted probability of failure and that the uncertainty arising from the jet grouting process can be experimentally quantified and rationally introduced in the analysis. Benefits and limitations of reinforcement with jet grouting are finally discussed by applying the proposed method to a case study.

Select this Article		A Comparison of Soil Thickness in a Zero‐Order Basin in the Oregon Coast Range Using a Soil Probe and Electrical Resistivity Tomography Michael S. Morse, Ning Lu, Jonathan W. Godt, André Revil, and Jeffrey A. Coe Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000717 Posted ahead of print 1 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract Accurate estimation of the soil thickness distribution in steepland drainage basins is essential for understanding ecosystem and subsurface response to infiltration. One important aspect of this characterization is assessing the heavy and antecedent rainfall conditions that lead to shallow landsliding. In this paper, we investigate the direct current (DC) resistivity method as a tool for quickly estimating soil thickness over a steep (33–40°) zero‐order basin in the Oregon Coast Range, a landslide prone region. Point measurements throughout the basin showed bedrock depths between 0.55 and 3.2 m. Resistivity of soil and bedrock samples collected from the site was measured for degrees of saturation between 40 and 92%. Resistivity of the soil was typically higher than that of the bedrock for degrees of saturation lower than 70%. Results from the laboratory measurements and point depth measurements were used in a numerical model to evaluate the resistivity contrast at the soil‐bedrock interface. A decreasing‐with‐depth resistivity contrast was apparent at the interface in the modeling results. At the field site, three transects were surveyed where coincident ground truth measurements of bedrock depth were available to test the accuracy of the method. The same decreasing‐with‐depth resistivity trend that was apparent in the model was also present in the survey data. The resistivity contour of between 1000–2000 Ω‐m that marked the top of the contrast was our interpreted bedrock depth in the survey data. Kriged depth‐to‐bedrock maps were created from both the field‐measured ground truth obtained with a soil probe and interpreted depths from the resistivity tomography, and were compared for accuracy graphically. Depths were interpolated as far as 16.5 m laterally from the resistivity survey lines with RMSE = 27 cm between the measured and interpreted depth at those locations. Using several transects and analysis of the subsurface material properties, the DC resistivity method is shown to be able to delineate bedrock depth trends within the drainage basin.

Select this Article		Experimental Validation of a Numerical Forward Model for Tunnel Detection Using Cross‐Borehole Radar Arvin Farid, M. ASCE, Jose A. Martinez‐Lorenzo, Akram N. Alshawabkeh, M. ASCE, and Carey M. Rappaport Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000716 Posted ahead of print 1 March 2012 Full Text: \| Download PDF
	+ -	Show Abstract The goal of this research is to develop an experimentally validated two‐dimensional (2D) finite difference frequency domain (FDFD) numerical forward model to study the potential of radar‐based tunnel detection. Tunnel detection has become a subject of interest to the nation due to the use of tunnels by illegal immigrants, smugglers, prisoners, assailants, and terrorists. These concerns call for research to nondestructively detect, localize, and monitor tunnels. Nondestructive detection requires robust image reconstruction and inverse models, which in turn need robust forward models. Cross‐Well Radar (CWR) modality is used for experimentation to avoid soil‐air interface roughness. CWR is not a versatile field technology for political boundaries but is still applicable to monitoring the perimeter of buildings or secure sites. Multiple‐depth wideband frequency‐response measurements are experimentally collected in fully water‐saturated sand, across PVC‐cased ferrite‐bead‐jacketed borehole monopole antennae at a pilot scale facility (referred to as SoilBED). The experimental results are then compared with the 2D‐FDFD model. The agreement between the results of the numerical and experimental simulations is then evaluated. Results of this work provide key diagnostic tools that can help to develop the algorithms needed for the detection of underground tunnels using radar‐based methods.

Select this Article		Load and Resistance Factor Design of Drilled Shaft in Sand D. Basu, M. ASCE and Rodrigo Salgado, F. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000714 Posted ahead of print 15 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract Resistance factors are developed for drilled shafts for a design method based on soil variables. The uncertainties associated with the design variables and equations were systematically quantified and Monte‐Carlo simulations were performed to obtain the distributions of the shaft and base capacities. Both the base and shaft capacities were found to follow normal distributions and the applied dead and live loads were assumed to follow normal and lognormal distributions, respectively. Reliability analysis was then performed to obtain the limit state and nominal resistances and loads for a variety of soil profiles and pile dimensions. The optimal dead and live load factors were subsequently obtained from the analysis. The optimal resistance factors were then adjusted for use with load factors recommended by FHWA.

Select this Article		Impact of Hydraulic Hysteresis on the Small‐Strain Shear Modulus of Low Plasticity Soils Ali Khosravi, Ph.D., S. M. ASCE and John S. McCartney, Ph.D., P.E., M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000713 Posted ahead of print 11 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract Experimental studies have observed that the small strain shear modulus (G_max) of unsaturated soils measured during hydraulic hysteresis has a greater magnitude during imbibition than during drainage when plotted as a function of matric suction. To capture this behavior, a semi‐empirical model was developed in this study to interpret the impacts of stress state and hydraulic hysteresis on G_max of low plasticity soils. Different from previous empirical relationships for G_max, this model incorporates elasto‐plastic constitutive relationships which integrate the effects of mean effective stress and hardening due to either plastic changes in volume or changes in the degree of saturation. The effective stress is defined as the sum of the net normal stress and the product of the effective saturation and matric suction, facilitating integration of the soil‐water retention curve parameters into the model. An experimental testing program involving measurement of G_max of compacted silt during hydraulic hysteresis was used to develop data to validate a methodology for model calibration. Specifically, hysteretic trends in G_max were defined for different mean net normal stress values using a fixed‐free resonant column device with suction‐saturation control. The proposed methodology to define the model parameters includes use of correlations from the literature as well as experimental measurements of G_max for soils in saturated conditions and during drainage. The model was found to fit the trends in experimental G_max data with suction, degree of saturation, and effective stress during drainage, and provided adequate prediction of the G_max data upon subsequent imbibition.

Select this Article		Shaft Friction from Instrumented Displacement Piles in an Uncemented Calcareous Sand B. M. Lehane, J. A. Schneider, J. K. Lim, and G. Mortara Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000712 Posted ahead of print 11 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract The behaviour of displacement piles in uncemented calcareous sand is investigated using field piles instrumented with a sensor that simultaneously records the radial stress and shear stress at specific locations on the pile shafts. These tests are interpreted with the assistance of data from adjacent self‐boring pressuremeter tests and from monotonic and cyclic direct shear interface tests performed on reconstituted samples. The existence of extremely low radial stresses on the pile shafts is verified. Although dilation during shear is seen to compensate for such low radial stresses, short term shaft capacities are much lower than capacities of equivalent piles in siliceous sands. The development of a ‘bonded’ or ‘welded’ crust to the pile shaft was seen to be the primary contributor to the set‐up observed at the test site; this crust forced failure to take place at a sand‐sand rather than a sand‐steel interface and also gave rise to higher levels of dilation during monotonic loading. The ‘welded’ sand crust did not, however, give rise to a higher long term cyclic capacity.

Select this Article		Stratified Response Surfaces for System Probabilistic Evaluation of Slopes Jian Ji and Bak Kong Low, F. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000711 Posted ahead of print 11 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract The need for probabilistic slope analysis that takes into account the uncertainty of soil properties has been acknowledged by the geotechnical profession. Traditionally, probabilistic slope analysis involves only single‐mode failure that is considered based on the critical slip surface. This may result in underestimating the failure probability. In contrast, system reliability analysis for slopes is deemed more rational. This study aims at improving the existing methods of slope reliability analysis by considering system reliability. A stratified response surface method (Stratified RSM) is proposed to describe the performance functions of possible failure modes. The proposed method differs from conventional response‐surface‐based slope reliability analysis (which constructs a single approximate performance function) by generating a group of (stratified) response surfaces. Based on these stratified response surfaces, system reliability analysis can be efficiently carried out by means of either FORM or Monte Carlo simulations. The efficient FORM based on the concept of a dispersion ellipsoid in the space of original variables is used. Application of the proposed approach to probabilistic assessment of slopes is illustrated by case studies, and the results obtained are compared with Monte Carlo simulations.

Select this Article		Buried Pipes in Rubber‐Soil Backfilled Trenches under Cyclic Loading S. N. Moghaddas Tafreshi, Gh. Tavakoli Mehrjardi, and A. R. Dawson Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000710 Posted ahead of print 10 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract In geotechnical engineering, recycled tires are used in lightweight fills, backfill materials, highway embankments, soil reinforcement and soil‐retaining walls. The rubber‐soil mixture can exhibit a greater capacity for energy absorbency than soil alone under cyclic loading and tends to decrease the stress and shocks transferred into the ground. The shear strength and energy absorbance of the rubber‐soil mixture is highly dependent on the size of the rubber fragments and the proportion in the soil. In this paper, soil surface settlement, pipe deflection and pressure distributed over a pipe placed in a trench and subject to cyclic loading were investigated as a function of chipped and shredded rubber used as backfill. The observed responses show the shredded rubber‐soil mixture used over the pipe is more effective in reducing these three parameters when covered by a soil cap, than using the same soil alone for the whole of the fill. Also using the rubber‐soil mixture in the whole of backfill without a soil cap delivers a negative influence on the responses. Overall, shredded rubber has a better performance as regards the pipe responses than the chipped rubber. By using a soil cap over the rubber‐soil mixture, the reduction in the subsequent soil settlement and plastic pipe deflection, attenuation of the pipe's accumulating strains and finally protection of the buried pipe from fatigue are achievable.

Select this Article		Tunnel‐Pile Interaction Analysis Using Cavity Expansion Methods Alec M. Marshall Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000709 Posted ahead of print 9 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract Evaluation of the impact of tunnel construction on existing buried structures is an important problem. This paper presents an analytical method for estimating the effect of tunnel construction on end‐bearing piles located above the tunnel. The method can be used to estimate the safe relative distance between existing piles and newly constructed tunnels. Spherical and cylindrical cavity expansion/contraction analyses are used to evaluate pile end‐bearing capacity and the reduction of confining pressure at the pile tip that results from tunnel volume loss. Pile end‐bearing capacity is then re‐evaluated based on the reduced confining pressure at the pile tip. A modified shear modulus is used to account for the effect of pile installation on soil stiffness. The method is used to analyse centrifuge experiments conducted to study this problem. For the experimental data, where the service load applied to the piles during tunnel volume loss ranged between 50% and 60% of the maximum jacking force, the analytical method showed that pile failure occurred when the load carrying capacity was reduced below 80% of its original value. A parametric analysis is included which highlights the effect of key soil properties on results.

Select this Article		Lateral Movements of Long Driven Piles during Pile Driving L. M. Zhang, M. ASCE and K. H. Chu Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000707 Posted ahead of print 7 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract Large lateral movements of a pile during impact driving can cause yielding of the surrounding soil. When this happens, the effective stress between the soil and the pile wall will diminish and the pile shaft resistance will decrease. A piling project was carried out in a marble area in Hong Kong, where highly variable rockhead contours and deep depressions filled with weak soil deposits were found. Many steel H‐piles were driven to depths over 100 m and the verticality of such long piles was a concern. A pile test program consisting of four driven steel H‐piles with pile lengths up to 164.5 m was conducted. Verticality monitoring and dynamic pile tests at several penetration depths were performed. This paper aims at interpreting the verticality of the four long piles, studying the relevance of pile verticality to the encountered geological features, and studying the effect of pile verticality on the pile capacity. The maximum lateral pile movement during driving was up to 8.7 m at a depth of 100 m and the maximum local pile inclination reached 0.139. The lateral movements of the piles during driving match well the rockhead inclination and soil conditions. Both one‐way sway and two‐way cyclic sway of the test piles were observed. Cyclic sway was shown to cause more severe reduction of the pile shaft resistance than one‐way sway.

Select this Article		Reliability of Spread Footing Performance in Desiccated Clay Armin W. Stuedlein, Ph.D., P.E. M. ASCE, Steven L. Kramer, Ph.D., P.E., M. ASCE, Pedro Arduino, Ph.D., M. ASCE, and Robert. D. Holtz, Ph.D., P.E., D.GE, Dist. M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000706 Posted ahead of print 7 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract To advance the use of reliability‐based design procedures, it is necessary to evaluate sources of design parameter uncertainty including inherent variability, measurement error, and transformation uncertainty. The results of a probabilistic evaluation of undrained footing bearing performance are discussed in the context of an extensive test site characterization described in a companion paper. Kriged cone tip resistance values are transformed into design parameters using a second‐moment probabilistic approach and compared to parameters obtained from laboratory test analyses on specimens retrieved from the test site. The spatial, measurement, and transformation uncertainty are incorporated into probabilistic finite element and bearing capacity analyses whose results are compared against a full scale load test performed at the test site. The results indicate that the reliable assessment of spread footing response depends to a large degree on assumed strength anisotropy and soil layering. Comparison of the probabilistic estimates of bearing capacity to deterministic estimates developed from correlations and average design parameters indicate that the consideration of uncertainty results in desirable prediction accuracy.

Select this Article		Soil—Foundation—Structure Interaction with Mobilization of Bearing Capacity: An Experimental Study on Sand V. Drosos, T. Georgarakos, M. Loli, I. Anastasopoulos, O. Zarzouras, and G. Gazetas, M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000705 Posted ahead of print 7 February 2012 Full Text: \| Download PDF
	+ -	Show Abstract Recent studies have highlighted the beneficial role of foundation uplifting and the potential effectiveness of guiding the “plastic hinge” into the foundation soil by allowing full mobilization of bearing capacity during strong seismic shaking. With the inertia loading transmitted onto the superstructure being limited by the capacity of the foundation, this concept may provide an alternative method of “in‐ground” seismic isolation: the so called rocking isolation. Attempting to unravel the effectiveness of this alternative design method, the paper experimentally investigates the nonlinear response of a surface foundation on sand and its effect on the seismic performance of an idealized slender single degree‐of‐freedom structure. Using a bridge pier as an illustrative prototype, three foundation design alternatives are considered, representing three levels of design conservatism. Their performance is investigated through static (monotonic and slow‐cyclic “pushover”) loading, and reduced‐scale shaking table testing. It is shown that rocking isolation may provide a valid alternative for the seismic protection of structures, providing encouraging evidence in favor of the innovative idea of moving foundation design towards a less conservative, even unconventional, treatment.

Select this Article		Effects of Waste Composition and Decomposition on the Shear Strength of Municipal Solid Waste Christopher A. Bareither, Craig H. Benson, and Tuncer B. Edil Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000702 Posted ahead of print 28 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract The objective of this study was to evaluate the effects of waste composition and decomposition on the shear strength of municipal solid waste. Waste was collected from two sources (an operating landfill and a transfer station) and degraded in laboratory anaerobic reactors to prepare wastes with different degrees of decomposition. Shear strength was measured in a 280‐mm‐diameter direct shear ring on nine wastes with normal stress ranging between 12 and 90 kPa. The Mohr‐Coulomb failure criterion was used to determine shear strength parameters (ϕ = friction angle and c = cohesion intercept) of the wastes, and shear strength was selected at a horizontal displacement of 56 mm (i.e., 20% of the specimen diameter). A composite failure envelope regressed through shear strength vs. normal stress data from all wastes was statistically significant, with ϕ = 37° and c = 20 kPa. A comparison between tests conducted in this study and in the literature indicates that larger ϕ are obtained for waste with a greater fraction of soil‐like, gravel, and inert constituents, whereas lower ϕ are coincident with higher fractions of paper and cardboard or plastic. This effect of waste composition on ϕ is applicable when fibrous particles are primarily parallel with the shear plane, which is the common particle orientation in direct shear. Tests conducted in this study also indicate ϕ increases with decreasing volatile solids or the ratio of cellulose + hemicellulose to lignin (i.e., increasing decomposition). Contrasting correlations have been reported in the literature, attributed to the initial waste composition, which influences the effect of decomposition on ϕ. No correspondence was found between c and waste composition or the degree of waste decomposition.

Select this Article		Relationship between the Seismic Coefficient and the Unfactored Geosynthetic Force in Reinforced Earth Structures Farshid Vahedifard, M. ASCE, Dov Leshchinsky, and Christopher L. Meehan, M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000701 Posted ahead of print 28 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract This paper presents an integrated analytical method for calculating the resultant unfactored geosynthetic force in reinforced earth structures under seismic loading conditions. The method utilizes a pseudostatic limit equilibrium approach for assessing the internal stability of a reinforced earth structure, assuming a potential rotational failure along a log spiral trace. A closed‐form solution is presented for determining the sum of all horizontal forces mobilized in the geosynthetic reinforcement along their intersection with the critical log spiral surface. This mobilized sum is then redistributed amongst the individual layers to determine the unfactored reinforcement forces that are needed to resist the applied seismic acceleration. Parametric studies were utilized and the results are presented in a series of design charts for different conditions. Such charts can be used to determine the required tensile strength of the reinforcement for a given seismic coefficient. Alternatively, for a given reinforcement strength, the formulation can also be used to determine the yield acceleration which is required for calculating seismic displacements. An advantage of the proposed methodology is that it determines the yield acceleration due to rotation of the reinforced mass (internal stability), which allows for a rational, yet simple, assessment of displacement as related to internal movement of the reinforced mass. The design charts illustrate the effect of earth structure backslope and vertical seismic coefficient. Furthermore, the results show the impact of the assumed location of the resultant reinforcement force under seismic loading conditions. Variations in the location of this force over a reasonable range have little impact on the results. The inclination of the backslope has a significant effect for earth structures with smaller batters and/or larger horizontal seismic coefficients. Additionally, vertical seismic coefficients with a downward direction increase the mobilized force in the geosynthetic reinforcement.

Select this Article		Probabilistic SPT‐Based Liquefaction Triggering Procedure Ross W. Boulanger, Professor, M. ASCE and I. M. Idriss, Professor Emeritus, Dist. M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000700 Posted ahead of print 28 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract A probabilistic version of the Idriss and Boulanger (2004, 2008) SPT‐based liquefaction triggering correlation is derived using a maximum likelihood approach and an updated case history database. Measurement and estimation uncertainties in the cyclic stress ratio (CSR) and SPT (N₁)_60cs values and the effects of the choice‐based sampling bias in the case history database are taken into account. The results of sensitivity analyses show that the position of the most likely triggering curve is well constrained by the case history data and that the magnitude of the total error term is also reasonably constrained. The most likely value for the standard deviation of the error term in the triggering correlation is, however, found to be dependent on the uncertainties assigned to the CSR and (N₁)_60cs. The results of the sensitivity study appear to provide reasonable bounds on the effects of different interpretations on the positions of the triggering curves for various probabilities of liquefaction. Methods for including model and parameter uncertainties in probabilistic liquefaction analyses are briefly discussed. The derived triggering correlation is compared to relationships developed from cyclic laboratory test results for specimens obtained using frozen sampling techniques.

Select this Article		Modeling Rock Fracture Intersections and Application to the Boston Area Herbert H. Einstein and Jean‐Lois Z. Locsin Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000699 Posted ahead of print 28 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract An algorithm for determining the intersections between fractures is presented in this paper. The algorithm is implemented in GEOFRAC, a stochastic fracture pattern‐modeling program. Previously, GEOFRAC allowed one to subdivide a fracture network into isolated sub‐networks in order to assess connectivity. GEOFRAC's new feature can be used to analyze length and orientation distributions of the fracture intersections. Connectivity parameters such as the number of intersections per unit volume, C₁, and intersection length per unit volume can be calculated. Intersections and connectivity are important since they govern the fluid flow and stability behavior of rock masses. The program is used to model fracture intersections in the Boston Area. Simulations show that for fractures in the Boston Area, the mean fracture intersection length ranges from 0.5 m to 0.7 m. Results also show that the relative frequency of long intersections (>2.0m) increases with increasing modeling volume size. In contrast to these effects of volume, it appears that intersection orientation is not affected by the volume being considered.

Select this Article		The Effect of the Porosity/Cement Ratio on the Compression of Cemented Soil Sara Rios, M.Sc., António Viana da Fonseca, D.Sc., and Béatrice Anne Baudet, Ph.D. Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000698 Posted ahead of print 16 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract The compression behavior of an artificially cemented soil was analyzed by means of the adjusted porosity/cement index using a correlation established in the recent literature. It was found that for each value of this index, defined as the ratio of porosity to the volumetric cement content, there is a unique Normal Compression Line (NCL). The NCLs of the cemented specimens for each adjusted porosity/cement index do not converge with the NCL of the uncemented silty sand at large stresses, but reach a line parallel to it, the lowest the adjusted porosity‐cement index, the further the NCL of the cemented sand from the NCL of the uncemented sand.

Select this Article		Compression and Creep of Venice Lagoon Sands Alex Sanzeni, Andrew J. Whittle, M. ASCE, John T. Germaine, M. ASCE, and Francesco Colleselli Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000696 Posted ahead of print 12 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract A laboratory test program has been conducted to evaluate the 1‐D compression and creep properties of intact sand (and silty‐sand) samples from a deep borehole at the Malamocco Inlet to the Venice Lagoon. The tests were performed with a CRS consolidometer and include special procedures for trimming the frozen samples, and measuring strains during thawing and back‐pressure saturation. The specimens have variable fine fractions ranging from 6 to 21% and mica contents ranging from 1 to 10%. The results confirm that there is a strong correlation between the creep rate coefficient and the compressibility index, and between the swelling index and mica content. The compression behavior in all tests is well described by the model proposed by Pestana and Whittle (1995) with a unique Limiting Compression Curve and a variable transition parameter that reflects the fines and mica content. Creep tests performed at different confining pressures are also well represented by a simple two‐parameter model.

Select this Article		Subgrade Undercut Criteria Based on Modeling of Rutting and Pumping Response Young Jin Park, Mohammed A. Gabr, Brent R. Robinson, and Roy H. Borden Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000695 Posted ahead of print 11 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract The stability of subgrade soils is a major concern during roadway construction with inappropriately soft layers often undercut and replaced by competent or stabilized materials. Systematic undercut criteria are established using numerical modeling with varying the strength and stiffness parameters of the subgrade and representing the mechanistic behavior of the subgrade as an elastic‐perfectly plastic medium. Two modes of domain configurations were considered: the plane strain and axisymmetric conditions. The plane strain mode is assumed to simulate proof roller loading with four parallel tires and mainly provides information about excessive pumping response as materials at deeper layers are affected. The axisymmetric mode provides information related to excessive rutting and is used to simulate the effect of single or dual tires representing construction traffic, rather than a series of closely spaced axle loads. Undercut criteria are proposed for on meeting a deformation limit state of 25 mm for both pumping and rutting with the additional requirement of Performance Capacity Ratio (PCR) of 1.5. The proposed criteria are applied to data from four field cases where decisions were made regarding the need for undercutting, and the applicability of the criteria is discussed.

Select this Article		Thermal Expansion and Contraction of Geomembrane Liners Subjected to Solar Exposure and Backfilling W. A. Take, E. Watson, R. W. I. Brachman, M. ASCE, and R. K. Rowe, F. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000694 Posted ahead of print 11 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract Geomembranes are widely used as advective barriers in landfill liner systems. When exposed to the sun, geomembranes exhibit a network of wrinkles due to thermal expansion. These wrinkles disrupt the intimate contact between the geomembrane and the underlying layer. If a hole is coincident with a geomembrane wrinkle then the space under the wrinkle has the potential to act as a preferential pathway for flow of contaminants. Thus, the size and shape of geomembrane wrinkles have implications for leakage rates through the composite liner system. However, wrinkles are only a concern if they persist after placement of backfill which is currently a subject of debate. In this paper, wrinkles are induced in a 1.5 mm thick black high density polyethylene strip geomembrane specimen overlying a geosynthetic clay liner using natural solar and laboratory energy sources. Particle Image Velocimetry (PIV) techniques are employed to record cross‐sectional wrinkle geometry during growth and subsequent backfilling. This cross‐sectional geometry is found to follow a Gaussian shape in which height increases with temperature and width remains relatively constant. Resulting relationships between height and temperature permit an estimation of wrinkle height for a known coefficient of thermal expansion for the geomembrane and an estimate of wrinkle spacing. For the GMB material and conditions tested, the results of the backfilling experiments indicate that when covered with 230 mm of cool sand (21°C), wrinkles of initial height less than about 20mm disappear completely, while larger wrinkles remain with a reduced height. Furthermore, wrinkles of 20 mm in height are observed to form with increases in geomembrane temperature of less than 5°C. With application to the field, these findings indicate that a geomembrane must be covered at or below its installation temperature to achieve a wrinkle‐free installation.

Select this Article		The Influence of Softening on the Mine Floor Bearing Capacity: A Case History Gennaro G. Marino, Ph.D., P.E., M. ASCE and Abdolreza Osouli, Ph.D., M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000693 Posted ahead of print 11 January 2012 Full Text: \| Download PDF
	+ -	Show Abstract This paper introduces a new approach which considers the effect of softening to more accurately calculate floor bearing capacities where difficult mine conditions are present. Due to softening and changes in confining pressures, the geotechnical properties of immediate fine‐grained rock vary in the mine floor. Therefore, when floor softening is present, the conventional equations used to determine the floor bearing capacity are not very accurate. In this study, a methodology is presented which considers the floor softening and existence of durable layer in the mine floor. The proposed method is based on analysis of a case study located in central Illinois utilizing finite element method (FEM) and rock mechanics laboratory data. For this case study extensive geological mapping and laboratory tests, including rock classification, rock swell properties and triaxial compression tests, were conducted on samples of fine‐grained rocks that predominantly consisted of mudstone. The results of laboratory tests are presented and discussed in detail. Aerial and cross‐sectional analyses of the floor lithology and stratigraphy were performed in order to evaluate the important bearing conditions across the project site. From the analyses, the immediate floor thickness and type of the non‐durable and the underlying durable rock across the site were determined. DuroIndex is presented and used to determine and rate the durability of mine floor material. Considering certain pillar‐to‐room width ratios, 2D FEM analyses were performed to evaluate mine floor capacity with both softened and unsoftened floor conditions. Consequently, the softening correction factor, or the correction for softening effect, was determined. Finally, a procedure which takes the effect of softening and existence of durable layer was developed to determine allowable floor bearing capacity.

Select this Article		Study of Non‐Uniform Bedding Support Due to Erosion under Cast Iron Water Distribution Pipes M. Balkaya, I.D. Moore, M.ASCE, and A. Sağlamer Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000689 Posted ahead of print 23 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract Several recent studies have investigated failure mechanisms for cast iron water pipes. These studies have primarily focused on the adverse effects of corrosion, frost, reactive backfill, and earthquakes. It now appears that leaking pressure pipes can produce erosion voids under the buried structure. In this paper, a parametric study employing three‐dimensional finite element analyses is used to examine buried, continuous, cast iron water pipe. The objective is to understand the effect of such erosion voids on the stability of buried cast iron pipes, and the longitudinal soil‐pipe interaction. The results of the finite element analyses demonstrate that the radial (σ_R), and the axial stresses (σ_A) are low compared to the hoop stresses (σ_θ), and the peak tension is always in the hoop direction. As a result of the high hoop stresses induced by the non‐uniform bedding support, longitudinal fractures are likely to occur in the pipe which may consequently cause pipe failure.

Select this Article		Investigation of Lateral Stress Relief using Finite Elements and Fracture Mechanics: A Case History Study of the Saxon Pit Walter G. Kutschke, PhD, PE, M. ASCE and Luis E. Vallejo, Ph.D., M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000688 Posted ahead of print 23 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract A published case history on the performance of a 29‐m deep excavation that occurred in stiff Oxford Clay provides direct field evidence that lateral stress relief can produce shear planes. A finite element model was developed to investigate the impact of lateral stress relief on this slope. The finite element model utilized published site characterization data and incorporated shear strength reductions along closed failure planes. Lateral stress relief resulted in an outward slope face movement that produced sufficient differential shear strain to develop and propagate a horizontal crack at the base of the slope. Analyses indicate excellent agreement with observed lateral and vertical slope face movements. The finite element model suggests that the slope essentially behaved as a shear model. Recognizing the behavior of this slope, the principles of linear elastic fracture mechanics are expanded to consider closed crack propagation under shear loading conditions. Analyses indicate that a closed crack under shear loading will propagate along the pre‐existing crack plane, as observed in the Oxford Slope.

Select this Article		Use of the Methylene Blue Stain Test to Evaluate the Efficiency of Lime Treatment on Selected Clayey Soils C. Cambi, S. Carrisi, and P. Comodi Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000687 Posted ahead of print 17 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract The Methylene Blue (MB) stain test was used to determine the efficiency of lime modification of clay soils and to define the percentage of lime required to reach the stabilization field. Montmorillonite and kaolinite, mixed in variable proportions with quartz sand, were treated with differing percentages of lime, and the MB test was performed on both untreated and treated soils. Results show that the test can determine whether a soil is prone to efficient modification, follows the evolution of clay minerals in the lime modification field, and also determines the quantity of lime necessary to enter the stabilization field. X‐ray powder diffraction, thermal analyses and electron microscopy observations of the montmorillonite‐richer sample showed its crystal chemical evolution in the modification field. Mineralogical results match the outcome of the MB test, defining the same lime percentage for best modification (4%) and confirming that the test can be used for preliminary and ongoing analyses of lime treatment.

Select this Article		Liquefaction Potential Assessment of Pleistocene Beach Sands in the Charleston Area, South Carolina Tahereh Heidari, A. M. ASCE and Ronald D. Andrus, M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000686 Posted ahead of print 17 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract Liquefaction potential of four Pleistocene beach sand deposits in the Greater Charleston area, South Carolina, is assessed in this paper. The assessment is based on a review of fifty‐one sites of conspicuous craterlets and horizontal ground displacement that occurred in beach sand deposits during the 1886 Charleston earthquake and an analysis of eighty‐two seismic cone penetration tests with pore pressure measurements. Of the fifty‐one ground failure sites, twenty‐three are associated with the Ten Mile Hill beds; thirteen with the Wando Formation; thirteen with the Silver Bluff terrace and younger deposits that lie adjacent to the harbor, rivers, and creeks; and two with the Ladson Formation. Liquefaction potential is analyzed using the seismic cone data with and without correction for age‐related processes (diagenesis), and then expressed in terms of the liquefaction potential index (LPI). Probability curves are developed from the LPI calculations for different earthquake ground shaking parameters. The probability curves for the Wando Formation over predict liquefaction potential when no corrections for diagenesis are made. When corrections for diagenesis are made, the probability curves for all four sands generally agree with the observed field behavior.

Select this Article		Two‐Dimensional Inversion of Full Waveforms Using Simulated Annealing Khiem T. Tran and Dennis R. Hiltunen, M. ASCE, P.E. Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000685 Posted ahead of print 17 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract The paper presents a technique to invert two‐dimensional (2‐D) full wavefields using simulated annealing and a finite‐difference solution of the 2‐D elastic wave equation in the time‐distance domain. The algorithm generates all possible wave types (body waves and surface waves, etc.) to simulate complex seismic wavefields and for comparison with observed data. Model runs with both synthetic and actual experimental data sets illustrate the capability of the inversion technique. The results from synthetic data demonstrate the potential of characterizing both low‐ and high‐velocity layers in laterally inhomogeneous profiles, and the inversion results from actual data are consistent with crosshole, SPT N‐value, and material log results. Based upon the cases presented, coupling of global optimization with full waveforms is computationally practical, as the results presented herein required less than one day of computer time on a standard laptop computer.

Select this Article		Simplified Procedure to Account for a Weaker Soil Layer in Lateral Load Analysis of Single Piles Christopher R. McGann, Pedro Arduino, and Peter Mackenzie‐Helnwein Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000684 Posted ahead of print 17 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract This paper presents a procedure to account for the presence of a weaker layer of soil in a beam on nonlinear Winkler foundation analysis of a laterally‐loaded pile or drilled shaft. 3D finite element models, considering a single pile embedded in a soil continuum, are used to compute representative p‐y curves for various combinations of soil profile and pile diameter. Comparisons between the p‐y curves resulting from homogenous and layered soil profiles, in which a weak soil layer is located between two stronger layers, provide the means to identify reductions in the ultimate lateral resistance and initial stiffness of the p‐y curves representing the stronger soil due to the presence of the weak layer. These reductions are characterized in terms of an exponential decay model. Dimensionless parameters are proposed as a means of implementing appropriate reductions for an arbitrary soil profile and pile diameter. Validation of the reduction procedure is conducted through a comparative study, in which the effects of liquefaction‐induced lateral spreading on a pile are analyzed using pseudo‐static nonlinear Winkler foundation and 3D finite element approaches. Use of the reduction procedure is demonstrated with p‐y curves defined by existing methods.

Select this Article		Examination and Re‐Evalaution of SPT‐Based Liquefaction Triggering Case Histories Ross W. Boulanger, Professor, M. ASCE, Daniel W. Wilson, Associate Director, M. ASCE, and I. M. Idriss, Professor Emeritus, Distinguished M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000668 Posted ahead of print 14 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract An SPT‐based liquefaction case history database for liquefaction triggering criteria is reexamined and re‐evaluated. The updated database incorporates a number of additional case histories, replaces prior estimates of earthquake magnitudes with current estimates of their moment magnitudes, uses improved estimates of peak ground accelerations when available, and includes a reexamination of the selection and computation of representative SPT (N₁)₆₀ values for most case histories. The approach used to select and compute representative SPT (N₁)_60cs values is illustrated using select case histories. The distribution of the case history data relative to the Idriss‐Boulanger triggering correlation (2004, 2008) is examined for any bias with respect to various parameters and to identify the conditions that are, and are not, well covered by available case history data.

Select this Article		Compression Behavior of Municipal Solid Waste: Immediate Compression Christopher A. Bareither, Craig H. Benson, and Tuncer B. Edil Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000672 Posted ahead of print 10 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract An evaluation of scale effects, stress, waste segregation, and waste decomposition on immediate compression behavior of municipal solid waste is presented. Laboratory experiments were conducted in 64‐, 100‐, and 305‐mm‐diameter compression cells. A field‐scale experiment (Deer Track Bioreactor Experiment ‐ DTBE) was conducted on waste of the same composition and material properties. A methodology is presented for determining the end‐of‐immediate compression strain (ϵ_EOI) that is applicable to both laboratory‐ and field‐scale data. The compression ratio (C_c’) was comparable between tests conducted in 100‐ and 305‐mm compression cells. Compression tests in 305‐mm cells conducted on six wastes (three size‐differentiated fresh wastes and three decomposed wastes) yielded C_c’ ranging from 0.22 to 0.28 in the stress range of 25–100 kPa. A similar C_c’ (0.23) was determined for the DTBE (20–67 kPa). Variation in C_c’ is related to the waste compressibility index (WCI), which is a function of waste dry weight water content, dry unit weight, and the percent contribution of biodegradable organic waste (paper/cardboard, food waste, yard waste). A compilation of laboratory data from this study and the literature yielded a predictive relationship for C_c’ and WCI. The C_c’ can be estimated within ± 0.087 for a given WCI using this relationship.

Select this Article		Abiotic and Biotic Compression of Municipal Solid Waste Christopher A. Bareither, Craig H. Benson, Tuncer B. Edil, and Morton A. Barlaz Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000660 Posted ahead of print 10 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract This study focused on quantifying relative contributions of abiotic and biotic compression of municipal solid waste (MSW). Abiotic mechanisms include immediate compression, mechanical creep, and moisture‐induced waste softening. The biotic mechanism is decomposition of the MSW organic fraction, which coupled with mechanical creep, yields biocompression. Three 610‐mm‐diameter laboratory compression experiments were conducted for 1150 d under the following conditions: (1) waste with no liquid addition (“dry”), (2) liquid addition spiked with biocide (“abiotic”), and (3) leachate recirculation (“biotic”). Immediate compression strain was similar in all three tests (24–27%). Mechanical creep, moisture‐induced softening, and biocompression were compared via time‐dependent compression ratios (C_α’). Moisture‐induced softening occurred in both the abiotic and biotic cells in response to liquid addition and leachate recirculation. Moisture‐induced softening accelerated the accumulation of mechanical creep (i.e., approximately doubled C_α’ due to mechanical creep relative to the dry cell), but did not increase the overall magnitude. C_α’ in the biotic cell correlated with methane flow rate when methanogenesis was controlled by the rate of solids hydrolysis. C_α’ due to mechanical creep in the dry cell and biocompression in the biotic cell increased exponentially with temperature, and can be represented with an exponential model. C_α’ due to biocompression was approximately one order of magnitude larger than C_α’ due to mechanical creep.

Select this Article		Deer Track Bioreactor Experiment: A Field‐Scale Evaluation of Municipal Solid Waste Bioreactor Performance Christopher A. Bareither, Ronald J. Breitmeyer, Craig H. Benson, Morton A. Barlaz, and Tuncer B. Edil Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000636 Posted ahead of print 10 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract The Deer Track Bioreactor Experiment (DTBE) was a field‐scale experiment conducted in a drainage lysimeter (8.2‐m height, 2.4‐m diameter) to assess the physical, chemical, and biological response of municipal solid waste with leachate addition. The experiment was operated for 1067 d, with leachate dosing initiated on Day 399. Fresh leachate collected from a full‐scale landfill was used for each dose. The ratio of cumulative leachate effluent to influent volume increased during dosing and leveled off at approximately 80%, indicating field capacity was achieved. Peak Darcy flux ranged from 2×10⁻⁷ m/s to 4×10⁻⁵ m/s, with larger flux computed for the last four doses when waste saturation was higher. During the experiment, the average dry unit weight of the waste increased 28% and the dry‐weight water content (w_d) increased 18% field capacity of the waste was 44 to 48% on a dry weight basis. Biochemical methane potential decreased from 51.4 to 3.4 mL‐CH₄/g‐dry, indicating that 93% of the potential methane embodied in the waste was removed. pH of the effluent increased, while biochemical oxygen demand (BOD), chemical oxygen demand (COD), and BOD:COD all decreased during dosing. Immediate compression occurred for 1–2 weeks following waste placement, and the immediate compression ratio (C_c’) was 0.23. The average rate of time‐dependent compression (C_α’) ranged between 0.048 and 0.35 and varied systematically with waste temperature (increasing C_α’ with increasing temperature).

Select this Article		Method for Estimating System Stiffness for Excavation Support Walls L. Sebastian Bryson, M. ASCE and David G. Zapata‐Medina, A. M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000683 Posted ahead of print 8 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract Excessive excavation‐induced movements are major concerns for most underground construction projects in urban areas. These movements can lead to significant damage in adjacent structures. When average to good workmanship is employed during the installation process of the excavation support systems, the consequent ground movements are most influenced by the support system stiffness. Therefore, choosing the most appropriate stiffness for an excavation support system is crucial to minimizing excavation‐related damage to adjacent buildings and utilities. This paper presents a semi‐empirical design methodology that facilitates the selecting of the excavation support system stiffness in such a way that limits excavation‐related ground movement. As part of the proposed design methodology, a new parameter was developed called the relative stiffness ratio. This new parameter relates the strength and stiffness of the soil with the stiffness of the excavation support system and was developed from a comprehensive parametric analysis that incorporated a fully three‐dimensional finite element analysis of a generalized excavation that realistically modeled the excavation geometry, the excavation support system configuration, and the excavation activities. The performance of the proposed methodology was evaluated using several excavation case histories reported worldwide. The results of the evaluation show that the new relative stiffness ratio performed well in predicting the support system bending stiffness and the actual excavation‐induced lateral deformations of the case history support systems.

Select this Article		Prediction of Frame Structure Damage Due to Deep Excavation Darwid Halim and Kai Sin Wong Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000682 Posted ahead of print 8 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract Ground movements caused by deep excavations may potentially lead to building damages in urban cities, where the majority of buildings are frame structures. A new damage chart, with two key parameters of the differential settlement and the frame dimensions, has been proposed. The chart has been validated against published data and field measurements obtained during the construction of mass rapid transit (MRT North East Line) in Singapore. The proposed chart can be used as an alternative or a supplement to other similar charts. Although the measurement of the frame dimensions is straight forward, the accuracy of the chart highly depends on the predicted building settlement, which still remains a challenge.

Select this Article		Small‐Scale Mechanical Properties of Biopolymers D. M. Cole, D. B. Ringelberg, and C. M. Reynolds Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000680 Posted ahead of print 8 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract The use of biopolymers to improve the engineering properties of soil has received attention in recent years, stimulated by potential cost savings and the low environmental impact of this class of materials. The motivation of the work presented here is to improve our understanding of precisely how biopolymers strengthen soil, and to quantifying the small‐scale mechanical properties of biopolymers for implementation in physics‐based numerical models. We describe our initial efforts to develop viable methods to form biopolymer bonds between grains of naturally occurring materials and present the results of mechanical properties experiments on these bonds. The subject biopolymer was an exopolysaccharide (EPS) from Rhizobium tropici (ATCC #49672). The initial experiments indicate that the stiffness of bonds ranged from 1 GPa after approximately one hour of curing to plateau values as high as 3.8 GPa for extended cure times. For bonds with neck areas in the range of 0.01 to 0.06 mm², the cohesive tensile strength of the bonds ranged from 16 to 62 MPa, but averaged ≈ 20 MPa. The associated cohesive failure strains in tension ranged from 0.013 to 0.042. Cyclic loading experiments were conducted to provide information on the mechanical behavior of the biopolymer and to support subsequent constitutive modeling. The results are analyzed and discussed in terms of the underlying viscoelastic behavior, paying particular attention to the variations in stiffness and internal friction as functions of cure time, frequency and amplitude.

Select this Article		Stability Assessment of Slopes Using Different Factoring Strategies Lysandros Pantelidis and D. V. Griffiths, F. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000678 Posted ahead of print 1 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract Traditional slope stability analysis delivers the factor of safety with respect to shear strength, which is the factor by which tan ϕ′ and c′ must be reduced in order to bring a slope to the point of failure. In the present paper, alternative strategies are considered to include the factors by which destabilizing parameters, such as pore pressures and gravitational loads, must be increased to bring a slope to the point of failure. The approach described gives a more comprehensive insight into the stability of slopes and the sensitivity of failure to different input parameters. Finally, the practical use of the alternative factoring strategies is illustrated through two application examples referring to a slope under different loading combinations (pore pressure ratio and horizontal seismic coefficient).

Select this Article		Analysis of Footing Load Tests on Aggregate Pier Reinforced Clay Armin W. Stuedlein, Ph.D., P.E., M. ASCE and Robert. D. Holtz, Ph.D., P.E., D.GE, Dist. M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000677 Posted ahead of print 1 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract Despite the increased use of aggregate piers for soil reinforcement, the role of typical construction variables on footing performance remains uncertain. This paper describes a series of full scale footing load tests conducted to evaluate the effect of aggregate gradation, pier length, and compaction method. Tests were conducted on small (0.76 m) and large (2.74 m) instrumented spread footings supported on single and groups of aggregate piers, respectively. The bearing pressure‐displacement response of these tests is presented, and statistical significance of construction variables quantified for single piers using a 2³ factorial analysis within an Analysis of Variance (ANOVA) framework. The statistical significance of the effect of pier length, gradation, and compaction were determined by controlling for the spatial variability in matrix soil strength and stiffness across the test site, and indicated that these variables were largely insignificant at the treatment levels evaluated. Additionally, no appreciable difference in the bearing pressure‐displacement performance of footings on groups of piers constructed with different levels of treatment was observed. Small variations in the observed displacement performance are attributed to sources of variability other than construction variables. The similarity in the performance of the uniformly constructed pier groups, representing production conditions, suggests that variations in the inherently variable matrix soil stiffness and strength control aggregate pier performance.

Select this Article		In‐Situ Pull‐Out Resistance of Dynamically Driven Nails Andrzej Sawicki and Marek Kulczykowski Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000676 Posted ahead of print 1 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract Experimental results concerning in‐situ pull‐out resistance of dynamically driven nails are presented. These results show that the actual pull‐out resistance is much higher than that predicted by the classical approach. A dimensional analysis approach is proposed to find a formula describing the actual performance of such nails.

Select this Article		Effects of Isolated Spread Footings on the Dynamics of Soil‐Structure Interaction Angeliki Papalou, M. ASCE, Jacobo Bielak, Dist. M. ASCE, and Enrique Bazán, M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000675 Posted ahead of print 1 December 2011 Full Text: \| Download PDF
	+ -	Show Abstract The objective of this work is to examine the dynamics of soil‐structure systems supported on isolated spread footings, in contradistinction with the rigid basemat often used in soil‐structure interaction (SSI) studies. By considering a column‐supported single‐story structure on isolated footings, we obtain an explicit formula for the fundamental natural period of the system. This allows us to examine the relative importance of the various system parameters that cause the natural period of the SSI system to increase compared to that of the corresponding fixed‐base system. The key parameter is the relative stiffness of an individual column to the rocking stiffness of the corresponding footing. If this parameter is small (< 0.5), there is little interaction (change in period < 20 percent). If it is large (> 4), the base of the column behaves essentially as a hinge, and the natural period tends to double with respect to that of the structure on a rigid base, just due to the effect of rocking of the individual footings. The lateral and vertical stiffness of the individual footings play a lesser role. Numerical results for a particular model illustrate this effect.

Select this Article		Base Capacity of Open‐Ended Steel Pipe Piles in Sand Feng Yu and Jun Yang, M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000667 Posted ahead of print 17 November 2011 Full Text: \| Download PDF
	+ -	Show Abstract This paper presents a new method for estimating the base capacity of open‐ended steel pipe piles in sand, a difficult problem involving great uncertainty in pile foundation design. The method, referred to as the HKU method, is based on the cone penetration test, and takes into consideration the mechanisms of annulus and plug resistance mobilization. In this method the annulus resistance is properly linked with the ratio of pile length to diameter (L/D) — a key factor reflecting the influence of pile embedment — whereas the plug resistance is related to the plug length ratio (PLR), which reflects the degree of soil plugging in a practical yet rational way. The cone tip resistance is averaged over a zone in the vicinity of pile base by taking into account the failure mechanism of piles in sand, the condition of pile embedment (i.e. full or partial embedment) and the effect of soil compressibility. The predictive performance of the new method is assessed against a number of well‐documented field tests including two fully instrumented large‐diameter offshore piles, and through comparisons with major CPT‐based methods in current engineering practice. The assessment indicates that the HKU method has attractive capabilities and advantages that render it a promising option.

Select this Article		Factors Affecting Efficiency of Microbially Induced Calcite Precipitation Ahmed Al Qabany, Kenichi Soga, and Carlos Santamarina Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000666 Posted ahead of print 17 November 2011 Full Text: \| Download PDF
	+ -	Show Abstract Microbial carbonate precipitation (MCP) using ureolytic bacteria shows promise in the field of geotechnical engineering for several different applications such as ground improvement and groundwater control. This study seeks to optimize the use and efficient control of Sporosarcina pasteurii to induce the precipitation of CaCO₃ in open environments. Laboratory tests were conducted to investigate the effect of changing treatment factors such as chemical concentrations, retention times and effective input rates (mole/liter/hr) on chemical efficiency. Chemical efficiency was measured based on weight measurements of CaCO₃ precipitation compared to the amount of chemical reactants injected to samples. Based on the experimental results, the optimum time required for the precipitation process to take place in porous media for a specific range of bacterial optical density was determined. Results show that, below a certain urea and CaCl₂ input rate of (0.042 mole/liter/hr) and for a bacterial optical density (OD₆₀₀) between 0.8–1.2, the reaction efficiency remained high and that the amount of precipitation was not affected by the liquid medium concentration (for input concentrations up to 1 M). However, the precipitation pattern at the pore scale was found to be affected by the injected concentration. Scanning electron microscopy (SEM) images taken of different samples at different levels of cementation showed that, for the same amount of precipitation, the use of lower chemical concentrations in injections resulted in better distribution of calcite precipitation especially at lower cementation levels. This variation in precipitation pattern is expected to affect the use of MCP for different applications.

Select this Article		Load and Resistance Factor Design (LRFD) Calibration for Steel Strip Reinforced Soil Walls Bingquan Huang, Richard J. Bathurst, and Tony M. Allen, M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000665 Posted ahead of print 17 November 2011 Full Text: \| Download PDF
	+ -	Show Abstract The paper reports the results of load and resistance factor design (LRFD) calibration for pullout and yield limit states for steel strip reinforced soil walls under self‐weight loading. An important feature of the calibration method is the use of bias statistics to account for prediction accuracy of the underlying deterministic models for reinforcement load, pullout capacity and yield strength of the steel strips, and random variability in input parameters. In order to improve the accuracy of reinforcement load predictions, small adjustments to current semi‐empirical AASHTO load design charts are proposed. Similarly, current empirical‐based design charts found in AASHTO and FHWA guidance documents for the estimation of the pullout resistance factor for smooth and ribbed steel strips are adjusted to improve the accuracy of pullout capacity predictions. The results of calibration lead to a load factor of 1.35 which is consistent with current practice and resistance factors that together give a consistent probability of failure of 1% for all three limit states considered. Furthermore, comparison with allowable stress design (ASD) past practice (AASHTO Simplified Method) shows that the operational factors of safety using a rigorous LRFD approach give the same or higher factors of safety and lower probabilities of failure. In this study, data for steel strip reinforced soil walls are used as an example to illustrate rigorous reliability theory‐based LRFD calibration concepts. However, the general approach is applicable to other reinforced soil wall technologies and calibration outcomes can be updated as more data become available.

Select this Article		Load and Resistance Factors for Internal Stability Checks of Mechanically Stabilized Earth Walls Dongwook Kim, A. M. ASCE and Rodrigo Salgado, F. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000664 Posted ahead of print 17 November 2011 Full Text: \| Download PDF
	+ -	Show Abstract This paper focuses on the development of LRFD for checks of the internal stability of MSE walls reinforced with steel strips. The internal stability of MSE walls relies on protection against two ultimate limit states (ULSs): pullout and structural failure of reinforcements. In this paper, we propose equations for the resistances and loads that reflect the physical processes involved in the pullout and structural failure ULSs and quantify the uncertainties in these equations. We then use these equations to perform reliability analyses using the first‐order reliability method (FORM) for different values of target reliability index in order to obtain load factors and resistance factors for use together with the equations in design. For a given target reliability index and vehicular load on top of an MSE wall, the resistance factor for pullout was highly dependent on reinforcement depth while that for structural failure was insensitive to changes in the design variables in its ULS equation.

Select this Article		Relationships between Particle Shape Characteristics and Macroscopic Damping in Dry Sands Andrea Ham, S. M. ASCE, Judith Wang, A. M. ASCE, and Jane G. Stammer Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000663 Posted ahead of print 16 November 2011 Full Text: \| Download PDF
	+ -	Show Abstract The objective of this study is to investigate relationships between scalar particle shape descriptors and macroscopic dissipative properties for dry, clean sands. To define these relationships in a consistent and useful manner, it is important to identify and examine relevant microscopic particulate shape characteristics and their effects upon macroscopic strain‐dependent damping ratio curves, ξ(γ), as measured by resonant column procedures. Scalar particle shape descriptors are examined to determine appropriate representative definitions for each of the three scales of particle shape (roughness, roundness, and sphericity), and Quantitative Mineralogy Scanning Technology (QEMSCAN) and image analysis procedures are used to quantify these representative particulate descriptors and specific surface for a significantly larger number of standardized sand samples' constituent particles than previously examined. Particle descriptor data are then projected to represent each standardized sand and related to shifts in small‐strain ξ(γ). From this study, it was found that roundness and roughness were more influential shape scales than sphericity and three representative scalar particulate descriptors (specific surface, Hayakawa and Oguchi (H/O) roundness, and solidity) display strong linear relationships with respect to measures of the slopes of each sand's ξ(γ).

Select this Article		Analysis of Climatic Influences on Slope Microseismic Activity and Rockfalls: The Case Study of the Matterhorn Peak (North‐Western Alps) Cristina Occhiena and Marina Pirulli Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000662 Posted ahead of print 16 November 2011 Full Text: \| Download PDF
	+ -	Show Abstract Rockfall instability is commonly preceded by the initiation and propagation of cracks. This process is accompanied by the release of microseismic energy, which can be detected by means of an appropriate monitoring system. A microseismic monitoring system and a thermometric monitoring system were installed on the Italian side of the Matterhorn peak, close to the J.A. Carrel hut, as part of the Interreg IIIA Alcotra “PERMAdataROC” project, as an increase in rockfall events had been observed. The objective of the installation was to establish whether this instability increase was connected to climatic fluctuations. A detailed analysis of the recorded microseismic data has shown a spatial concentration of the microseismic activity on the western side of the investigated slope, while a correlation of these data with thermal information has shown that the temporal concentration of the microseismic activity could be traced back to the transition from warm to cold periods. It has also emerged that cold periods, characterized by a continuous and more rapid temperature decrease in time, present the higher value of the average daily number of events.

Select this Article		Trace Elements Leaching from Organic Soils Stabilized with High Carbon Fly Ash Jacob J. Sauer, Craig H. Benson, Ahmet H. Aydilek, and Tuncer B. Edil Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000653 Posted ahead of print 3 November 2011 Full Text: \| Download PDF
	+ -	Show Abstract Leaching of four trace elements [cadmium (Cd), chromium (Cr), selenium (Se), and silver (Ag)] from soft organic soils stabilized with high carbon fly ashes (HCFA) was assessed using water leach tests (WLTs) and column leach tests (CLTs) on soil alone, fly ash alone, and soil‐fly ash mixtures. Concentrations from WLTs on soil‐fly ash mixtures were lower than concentrations from WLTs on fly ash alone, and were controlled more by the fly ash than the soil. However, dilution calculations based on tests on soil alone and fly ash alone were unreliable. Thus, leaching assessments should be conducted directly on soil‐fly ash mixtures. Leaching patterns from the CLTs followed first‐flush and lagged‐response patterns with comparable frequency, although first‐flush patterns were more common with fly ash having higher CaO content. Cd and Cr exhibited first‐flush leaching more frequently, Ag a lagged‐response pattern more frequently, and Se exhibited first‐flush or lagged‐response patterns with similar frequency. pH had a strong effect on leaching concentrations, with lower concentrations of Ag and Cd and higher concentrations of Cr at higher pH. Peak concentrations of Ag and Cd for flow‐through conditions can conservatively be estimated as 50 times the WLT concentration, whereas a factor of 100 should be applied for Cr and Se for organic soil‐HCFA mixtures.

Select this Article		Effects of Axial Load and Slope Arrangement on Pile Group Response in Laterally Spreading Soils J. A. Knappett and S. P. G. Madabhushi Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000654 Posted ahead of print 3 November 2011 Full Text: \| Download PDF
	+ -	Show Abstract This paper presents the results of a series of dynamic centrifuge tests which were conducted for 2 × 2 pile groups in a three‐layer laterally spreading soil profile consisting of a non‐liquefiable cohesive crust overlying loose, liquefiable sand, overlying dense sand. Two main variables are considered which have received little attention in previous work on piles in laterally spreading soils, namely 1) the axial load carried by the foundation and 2) whether the slope boundary conditions are infinite or finite. The data show that the presence of axial load reduces the lateral stiffness of the foundation due to P‐Δ effects and reduces their capacity to resist lateral kinematic loads from spreading soil. This degradation in lateral response (bending) may be accompanied by substantial settlement of the foundation as a competing failure mode which must also be considered in design. Furthermore, the mechanical response of the liquefied soil appears to vary greatly with the slope boundary condition. This is particularly true at the interface between the liquefied sand and the cohesive crust, where the downslope displacement of the crust for infinite slopes is much greater than the underlying sand, with the reverse being true for finite slopes. The data also suggest an alternative mechanism to the water‐film concept which has been used previously to account for the large downslope movements of low permeability crustal layers. This fundamental difference in mechanical response provides insight which may lead to the improvement of simplified empirical methods for estimating surficial displacements due to lateral spreading.

Select this Article		Monitoring Twin Tunnel Interaction Using Distributed Optical Fiber Strain Measurements Hisham Mohamad, Kenichi Soga, Peter J. Bennett, Robert J. Mair, and Chi Sharn Lim Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000656 Posted ahead of print 3 November 2011 Full Text: \| Download PDF
	+ -	Show Abstract In this field trial, a new monitoring technique using distributed strain sensing known as Brillouin Optical Time Domain Reflectometry (BOTDR) was introduced to monitor the behavior of bolted‐concrete linings of a recently completed tunnel when a second bored tunnel was constructed side by side at a distance less than one tunnel diameter apart. This was done by measuring circumferential strains in 12 rings using optical fiber that was installed using the point‐fixing method. The strain distributions around the circumference of the rings show a generally similar profile. Maximum compressive strains measured below the tunnel springline nearest to the excavated tunnel were larger than the maximum tensile strains measured at the tunnel crown, distorting the circular tunnel into an oval/ellipsoid that was about symmetrical to the horizontal axis. Several methods were introduced in order to compare strain measurements made by BOTDR and diameter changes recorded by tape extensometer. This involves the use of a symmetrical tunnel distortion model and the basic differential equation for a circular arch. The calculated results showed some degree of similarity between the two methods. The analysis highlighted the importance of measuring the axial strain in the tunnel ring and subtracting the axial strain component in order to calculate the actual deflection of the lining due to bending.

Select this Article		Metamorphosing the SASW Method by 2‐D Wavefield Transformation Chun‐Hung Lin and Chih‐Ping Lin Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000657 Posted ahead of print 3 November 2011 Full Text: \| Download PDF
	+ -	Show Abstract The dispersion analysis in a surface wave testing is conventionally associated with a certain method of data acquisition, for example, the phase angle analysis in the two‐station SASW method and the 2‐D multi‐station wavefield transformation in the MASW method. A new procedure have been developed to reconstruct the SASW data as MASW‐imitating data, taking advantages of the 2‐D multi‐station wavefield transformation to better analyze the SASW data. Numerical simulations and a real world example demonstrated the feasibility, but also reveal a side effect associated with aliasing. A common‐receiver survey is further proposed for future experiments to eliminate the un‐wanted side effect and at the same time increase the lateral resolution.

Select this Article		On the Evaluation of Soil Dynamic Properties in Centrifuge Tests Riccardo Conti and Giulia M. B. Viggiani Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000659 Posted ahead of print 3 November 2011 Full Text: \| Download PDF
	+ -	Show Abstract This paper describes a method to compute the mobilised shear modulus, G, and damping ratio, D, using the non‐linear fit of experimental transfer functions obtained at different depths in centrifuge models with the analytical expression of the amplification function for a visco‐elastic soil layer on a rigid base. The corresponding shear strain, γ, is computed as a function of the particle velocity and shear wave velocity. The sources of potential error in the determination of G, D, and γ embedded in the proposed method are identified and discussed in comparison with two other methods that have been proposed in the literature, based either on the determination of the time lag of accelerations between two accelerometers or on the evaluation of the shear stress‐shear strain cycles from acceleration time histories recorded at different depths in the model. The performance of the three methods is evaluated using the experimental data obtained from nine centrifuge tests on dry sand. The values of G obtained by the proposed method compare very well with the results of laboratory and literature data; D values are more dispersed and slightly above literature data.

Select this Article		Predicting the Onset of Static Liquefaction of Loose Sand with Fines M. M. Rahman and S. R. Lo Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000661 Posted ahead of print 3 November 2011 Full Text: \| Download PDF
	+ -	Show Abstract Loose sandy soil subject to undrained shearing manifests deviatoric strain softening and such a behavior has been referred to as collapse, static liquefaction or instability. This note uses the term instability and characterizes its triggering by the corresponding effective stress ratio, referred to as instability ratio, η_IS. In order to capture the influence of fines on η_IS, the state parameter, ψ, as originally proposed by Been and Jefferies was generalized to equivalent granular state parameter, ψ^∗. This is achieved simply by replacing void ratio, e, with equivalent granular void ratio, e^∗. The conversion from e to e^∗ was achieved by a predictive approach and back‐analysis is not required. It was hypothesized that, provided the fines content is less than the threshold value, η_IS and ψ^∗ at start of undrained shearing can be described by a single relationship irrespective of fines content. Two published databases and a series of undrained triaxial tests results are used to evaluate this hypothesis. The importance of this relation is significant as it can be used to predict η_IS for sand with different fines content.

Select this Article		Reliability‐Based Underseepage Analysis in Levees Using a Response Surface‐Monte Carlo Simulation Method John D. Rice and Lourdes Polanco Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000650 Posted ahead of print 24 October 2011 Full Text: \| Download PDF
	+ -	Show Abstract Current methods for assessing the potential for unsatisfactory levee performance due to underseepage consist of deterministic seepage analyses and simplified reliability methods. Deterministic methods consist of calculating Factors of Safety based on the ratio of the critical gradients of the soil and hydraulic exit gradients without taking into account high levels of uncertainty in soil properties and subsurface geometry that are inherent to many levee analyses. The most common simplified reliability approaches currently being used to analyze levees against underseepage apply the First‐Order Second‐Moment Taylor Series method using the US Army Corps of Engineers Blanket Theory Equations as the performance functions. In many cases, these methods do not realisticly reflect the geometry of the levee's foundation soils and the uncertainty associated with their performance. A new application for the Response Surface Method is proposed that allows modeling the initiation of erosion process with more accurate failure mechanisms and more complex subsurface geometry. The Response Surface ‐ Monte Carlo (RSMC) Simulation Method uses finite element analyses to develop a series of equations that define the relationship between the variables and the Factor of Safety (F). Using these equations, Probability Density Functions (PDF) for variables, and the computer program @Risk, a Monte Carlo simulation is performed to calculate the conditional probability of unsatisfactory performance due to underseepage for a given river flood level. Two examples are presented to illustrate the proposed procedure. Multiple regression analyses are performed to assess the relative effect that changes in the input variables have on the F for the various analyses. The results suggest that uncertainty in the levee geometry has the greatest effect on the variation of the F for the cases studied.

Select this Article		Modified UH Model: Constitutive Modeling of Overconsolidated Clays Based on a Parabolic Hvorslev Envelope Yangping Yao, Zhiwei Gao, Jidong Zhao, and Zheng Wan Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000649 Posted ahead of print 20 October 2011 Full Text: \| Download PDF
	+ -	Show Abstract Most clays, either naturally deposited or man‐made, possess certain degree of overconsolidation due to tamping, cyclic loading, erosion, excavations, and/or changes in ground‐water tables. An easy‐to‐use constitutive model for overconsolidated clays is useful for relevant engineering applications. In this paper, a simple model is proposed for overconsolidated clays based on a previous one developed by the authors (the Unified‐Hardening model or in brief the UH model). To evaluate the potential peak stress ratio of overconsolidated clays, we adopt a parabolic Hvorslev envelope rather than a straight one in the original UH model. The proposed parabolic Hvorslev envelope passes through the origin of the mean stress‐deviatoric stress plane. It has a slope of three as the overconsolidation ratio (OCR) approaches infinite and intersects with the critical state line as OCR reaches unit. This modification leads to more realistic predictions for highly overconsolidated clays than the original UH model with a straight Hvorslev envelope does, and is consistent with the critical state soil mechanics that the higher peak stress ratio in overconsolidated clays is a result of interlocking (or dilatancy) rather than cohesion. The modified UH model retains the same parameters as those in the Modified Cam‐Clay model. Reasonable agreement between the model predictions and experimental data demonstrates that the modified model is capable of addressing the fundamental behavior of overconsolidated clays. The present model is developed for reconstituted clays with isotropic fabric. Discussion is made on potential improvement of the model to take into account of anisotropy and structural effect.

Select this Article		Experimental Investigation of Epoxy Resin and Sand Mixes C. A. Anagnostopoulos and T. T. Papaliangas Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000648 Posted ahead of print 20 October 2011 Full Text: \| Download PDF
	+ -	Show Abstract The use of new materials for soil strengthening is crucial for geotechnical engineering, ‐ especially in foundation construction. The main objective of this study was to investigate the potential use of two‐component water soluble epoxy resins to improve the physical and mechanical properties of medium sand, because the efficacy of these resins on soil strengthening has not yet been properly investigated. The experiments were conducted using resins with different epoxy resin‐to‐water (ER/W) ratios. The results of this study indicate that the epoxy resins improve the physical and mechanical properties of the sand significantly, and if successfully grouted into a formation, the resins could provide a suitable solution for the stabilization of the foundation material. Based on the experimental results, a non‐linear regression analysis was performed to correlate the mechanical properties and permeability with the curing time and ER/W ratio.

Select this Article		Design Procedure and Considerations for Piers in Expansive Soils John D. Nelson, Ph.D., P.E. F. ASCE, Erik G. Thompson, Ph.D., P.E., Robert W. Schaut, P.E., M. ASCE, Kuo‐Chieh Chao, Ph.D., P.E., M. ASCE, Daniel D. Overton, P.E., F. ASCE, and Jesse S. Dunham‐Friel, E.I.T., Aff. M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000647 Posted ahead of print 20 October 2011 Full Text: \| Download PDF
	+ -	Show Abstract The design of pier foundations in expansive soils is an important and challenging aspect of geotechnical engineering. Established methods for pier analysis include rigid and elastic methods. These methods have certain limitations that restrict their applicability to evaluate certain complex aspects of pier heave including variable soil profiles, complex wetting profiles, large length‐to‐diameter ratios, and complex pier configurations and materials. To address those limitations, a method of analysis was developed providing a versatile and robust tool to predict both pier heave and axial forces developed by expansive soils. This method utilizes a standard finite element code to solve for pier heave and force in the pier for the given boundary conditions. This paper contains both a discussion of the general design procedure and a discussion of the finite element formulation. This design procedure, including the finite element code, accurately determines pier heave and force in a pier when compared to field‐measured data. The design procedure and the finite element code in particular, address the limitations of the established rigid and elastic pier analysis methods with the flexibility to evaluate complex design situations. Comparison with field measured pier heave and tensile force in the pier demonstrates that the design procedure accurately models both the magnitude of pier heave and force in the pier. The results obtained using this design procedure have been compared with those obtained using the established pier analysis methods for simplified drilled pier examples. The comparison of the various methods of analysis demonstrates that the finite element design procedure predicts pier heave values that are generally less than the existing elastic and rigid pier analysis methods. It is believed that the proposed design method is more realistic and provides a design tool with improved accuracy compared to existing methods.

Select this Article		Soil Investigation of Fly Ash Deposit Improved by Heavy Compaction Method T. Kokusho, S. Nakashima, A. Kubo, and K. Ikeda Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000644 Posted ahead of print 20 October 2011 Full Text: \| Download PDF
	+ -	Show Abstract An in situ test program was undertaken to systematically investigate the effectiveness of HCM (heavy compaction method) normally used for sandy soils for compacting fly ash deposit. Measurements of soil performance and cone penetration tests before and after the compaction were carried out, indicating obvious effects on soil properties and strength increase in the improved ground. It has been found that HCM introduces 3‐dimensional non‐uniformity in the upper part versus horizontally uniform layers in the lower part of the improved ground. Also found is that the HCM‐induced vertical soil strain is almost proportional to the ratio of cone resistance increment to the prior‐treatment cone resistance in the uniform zones.

Select this Article		Large‐Scale Quantification of Wrinkles in a Smooth, Black, HDPE Geomembrane M. J. Chappel, R. W. I. Brachman, M. ASCE, W. A. Take, and R. K. Rowe, F. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000643 Posted ahead of print 17 October 2011 Full Text: \| Download PDF
	+ -	Show Abstract Wrinkles are buckles (or waves) that develop from restrained thermal expansion when the geomembrane is left exposed to solar heating. Wrinkles can substantially reduce the effectiveness of the geomembrane as a hydraulic barrier if a hole is at or near a wrinkle, depending on the number, length and width of wrinkles. Low altitude aerial photography and digital image analysis are used to quantify the nature and extent of wrinkles that developed over one hot and sunny day in a smooth, black, 1.5‐mm‐thick HDPE geomembrane over a 55 m by 140 m area. Wrinkles were found to significantly vary over the course of the day, increasing from the fewest wrinkles in the morning to a maximum just after noon before decreasing towards the late afternoon. For the specific conditions examined, wrinkles were found to occupy 3%, 21% and 7% of the entire area surveyed at 8:45, 12:25 and 17:15, respectively. Connections between adjacent wrinkles were observed to create significant interconnected wrinkle features greater than 2000 m long. The shortest maximum interconnected wrinkle feature of 80 m/ha was measured at 8:45 while the longest such feature was 6600 m/ha at 13:45. The observations and results provide data to support the approach that limiting the time of day when cover is placed on geomembrane can be very effective at reducing the extent of wrinkling.

Select this Article		Design Guidelines and Full Scale Verification for MSE Walls with Traffic Barriers K.‐M. Kim, J.‐L. Briaud, R. Bligh, and A. Abu‐Odeh Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000642 Posted ahead of print 6 October 2011 Full Text: \| Download PDF
	+ -	Show Abstract Millions of square meters of mechanically stabilized earth (MSE) retaining walls are constructed annually in the United States. For highway applications, a roadside barrier system is placed at the edge of the wall. This barrier system generally consists of an L shape concrete structure so that if a vehicle hits the vertical part of the L shape (barrier), the horizontal part of the L (moment slab) provides the resisting moment during the impact. This impact must be resisted by the soil, the reinforcement, and the panels in the MSE wall. This paper gives guidelines on how to design the reinforcement for pull out and yielding, and the panels for flexural and shear failure. It also gives the guidelines on how to ensure the stability of the barrier. These design guidelines are developed in terms of AASHTO LRFD procedures. In a second part a full‐scale crash test on an instrumented 2.79 m high MSE wall is described and analyzed. The wall and barrier behaved very satisfactorily and represented a verification of the proposed guidelines. Pressure distributions are presented for designing the top two layers of wall reinforcement to resist barrier impact forces. A 44.5 kN static equivalent load is recommended for evaluating the stability of the barrier and moment slab system.

Select this Article		Effective Stress Soil Model Calibration Based on In‐Situ Measured Soil Properties Zhi‐Liang Wang, Faiz I. Makdisi, and Fenggang Ma Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000641 Posted ahead of print 30 September 2011 Full Text: \| Download PDF
	+ -	Show Abstract Numerical analyses for soil structures under monotonic and cyclic loading using non‐linear models have developed rapidly in recent years. Effective stress‐based soil models are incorporated in the analyses to predict soil deformation and/or liquefaction. However, in applications to engineering projects, model parameter calibration often becomes an obstacle to the practical use of the model due to the uncertainties and unavailability of appropriate laboratory test results. This article proposes a procedure to calibrate a soil model for simulating liquefaction and ultimate failure state under monotonic and/or cyclic loading, using data based on in‐situ measurements in the standard penetration test (SPT). The ultimate failure state that limits soil dilation is based on residual strength and void ratio correlation, and the state‐dependent dilatancy concept. A relationship between soil liquefaction resistance and equivalent number of cycles is developed based on published SPT‐based liquefaction triggering charts, together with correlations between a magnitude scaling factor and number of equivalent cycles to liquefaction. Examples to illustrate the application of these concepts are also presented.

Select this Article		Case History of Installing Instrumented Jacked Open‐Ended Piles Jun‐wei Liu, Zhong‐miao Zhang, Feng Yu, and Zhi‐zhuan Xie Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000638 Posted ahead of print 23 September 2011 Full Text: \| Download PDF
	+ -	Show Abstract Construction effects on the pile‐soil system arise from the process of installing displacement piles. A comprehensive field test program complemented with laboratory tests is carried out to observe the performance of jacking open‐ended concrete pipe piles into silt deposit. The jacked piles are found in a plugged mode during installation. Direct observation on the soil plug reveals that its formation generally accords with the stratigraphic nature of the layered soils. Soil‐arching behavior during pile penetration causes that the soil in the shear zone along the inner pipe wall mainly comes from the uppermost layer of the deposit. Laboratory tests on the soil plug shows evident compaction and tendency of strength increase with time. The buildup of the excess pore pressure and radial total stress in the soil is sensitive to the jacking installation procedure. By taking into account the soil displacement related to the plugging degree, the captured peak excess pore pressure at a given horizon can be modeled by the cavity expansion theory that normally adapts to closed‐ended pile. The jacking annulus resistance normalized by the cone tip resistance is independent of the penetration depth and the degree of plugging. A considerable portion of the annulus resistance is locked in the pile after installation, decreases a little during adjacent pile installation and remains stable in long period.

Select this Article		New Correlation Equations for Compression Index of Remolded Clays Binod Tiwari, Ph.D., M. ASCE and Beena Ajmera, S. M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000639 Posted ahead of print 23 September 2011 Full Text: \| Download PDF
	+ -	Show Abstract Compressibility of a soil mass is one among the most important geotechnical properties that is widely used during the design of geotechnical structures. Various regression equations were proposed by numerous researchers in the past to estimate the compression index of a soil specimen with parameters such as void ratio at liquid limit, initial void ratio, liquid limit, or the combination of the specific gravity, void ratio, and liquid limit. Although all researchers concur that the compression index depends on the mineralogical composition of the soil and initial moisture content, very few researches have been performed on the mixtures of minerals composing a wide range of activities under consistent initial moisture contents. This research is conducted on 55 different soil specimens prepared in the laboratory by mixing various proportions of montmorillonite, illite, kaolinite, and quartz at initial moisture contents equal to the liquid limit. Intrinsic Compression Line (ICL) was unique for most of the mixtures used for this study. Very good regressions were obtained between the compression index and initial void ratio, initial porosity, plasticity index or liquid limit. Two different equations were proposed to estimate the compression indices of remolded clays with liquid limit — one for soils with activities less than one and the other for soils with activities higher than one. The compression indices of 82 different natural samples, reconstituted at liquid limit, were similar to the values estimated with the proposed equations. Furthermore, the compression indices of the soil samples presented in literature could also be estimated with reasonable accuracy using the proposed equations.

Select this Article		Reliability‐Based Design of Augered Cast‐in‐Place Piles in Granular Soils Armin W. Stuedlein, Ph.D., P.E., M. ASCE, William J. Neely, Ph.D., P.E., M. ASCE, and Thomas M. Gurtowski, P.E., M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000635 Posted ahead of print 14 September 2011 Full Text: \| Download PDF
	+ -	Show Abstract Although a variety of methods exist to estimate axial capacity for augered cast‐in‐place piles, they are generally limited to Allowable Stress Design (ASD) procedures with little consideration of design reliability. This paper describes the addition of static loading test results to a global augered cast‐in‐place pile dataset to assess the accuracy of new and existing design methods and to address the current lack of reliability‐based design methods for augered cast‐in‐place piles. The new static loading tests in Western Washington were carried out on piles installed in granular materials, with pile diameters and lengths ranging from 0.41 to 0.51 m and 9.5 to 29 m, respectively. The preparation of Beta coefficients and unit toe bearing resistance values is discussed within the framework of strain dependent composite tangent moduli and observed residual loads. New relationships for the Beta‐coefficient and toe bearing resistance values are proposed, and the accuracy of new and existing design procedures is statistically characterized using the updated global dataset. Resistance factors for axial compression and uplift are calibrated at the strength limit for use in Load and Resistance Factor Design (LRFD).

Select this Article		Sand Deformation around an Uplift Plate Anchor Jinyuan Liu, P.E., P. Eng., M. ASCE, Mingliang Liu, and Zhende Zhu Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000633 Posted ahead of print 9 September 2011 Full Text: \| Download PDF
	+ -	Show Abstract This paper presents an experimental investigation on soil deformation around uplift plate anchors in sand by using digital image correlation (DIC). The experimental setup consists of a camera, loading frame, plexiglass mould, and computer, which is developed to capture soil deformation during anchor uplifting. A series of model tests are performed to investigate the influence of particle size, soil density, and anchor embedment depth on soil deformation. A set of images captured during anchor uplifting are used to calculate soil displacement fields by DIC. The failure surface is studied by tracking the points with maximum shear strain values. Based on this study, it is found that soil deformation and the pullout resistance of plate anchors are substantially influenced by soil density and anchor embedment depth, while particle size within the studied range has limited influence. In dense sand, the shape of the failure surface changes from a truncated cone above a shallow anchor to a combined shape of a curved cone and a truncated cone for a deep anchor. In contrast, in loose sand a cone‐shaped failure surface is formed within the soil mass above a shallow anchor; while no failure surface is observed for a deep anchor, where the compressibility of soil is the dominating factor that influences the behavior of deep plate anchors in loose sand.

Select this Article		Influence of Non/Low‐Plastic Fines and Associated Aging Effects on Liquefaction Resistance Takaji Kokusho, M. ASCE, Fumiki Ito, Yohta Nagao, and Russell A. Green, M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000632 Posted ahead of print 9 September 2011 Full Text: \| Download PDF
	+ -	Show Abstract The objective of the study presented herein is the development of an understanding of the influence of non/low‐plastic fines and associated aging effects on the penetration resistance (q_t) and liquefaction resistance (R_L) of sandy soils. Towards this end, the authors performed a series of cyclic triaxial tests on samples having varying relative densities (D_r) and fines contents (F_c), wherein a miniature cone was incorporated into the triaxial apparatus. This allowed the penetration resistance and the liquefaction resistance to be determined directly for the same samples. To simulate geologic aging effects, a small amount of cement was mixed in with the soil during sample preparation. From “un‐aged samples” without cement, it was found that although both R_L and q_t decrease as F_c increases, a unique relationship exists between R_L and q_t that is independent of F_c. However, from samples having the same C_c/F_c (i.e., simulating the same geologic age), it was found that R_L increases as F_c increases for the same q_t. This trend is consistent with field‐based R_L ‐ q_t correlations for natural soil deposits to which aging effects are intrinsic. Thus, it has been clarified that not the F_c⁻ value by itself but rather the cementation effect associated with higher F_c results in a higher liquefaction resistance for a given q_t.

Select this Article		Modeling Volatile Organic Compound Transport in Composite Liners Min‐Gyun Park, Tuncer B. Edil, F. ASCE, and Craig H. Benson, F. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000630 Posted ahead of print 9 September 2011 Full Text: \| Download PDF
	+ -	Show Abstract Data from bench‐scale composite liner experiments were compared to predictions made with two models (a finite‐difference model and a semi‐analytical model) used to predict volatile organic compound (VOC) transport through composite liners. Transport parameters for the geomembrane and clay for five common VOCs were measured independently and used as input. Predictions from both models for all five VOCs were essentially identical. Excellent agreement was obtained between the predicted and measured concentrations for all five VOCs without model calibration. However, inherent variability in measured transport parameters has a significant effect on predictions. VOC concentrations in the clay liner near the geomembrane‐clay interface depend primarily on transport parameters for the geomembrane. However, this becomes less significant as the distance from the geomembrane‐clay interface increases.

Select this Article		Field Investigations on Performance of T‐Shaped Deep Mixed (TDM) Soil‐Cement Columns Supported Embankment over Soft Ground Song‐Yu Liu, M. ASCE, Yan‐Jun Du, Yao‐Lin Yi, and Anand J. Puppala, M. ASCE Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000625 Posted ahead of print 1 September 2011 Full Text: \| Download PDF
	+ -	Show Abstract The soil‐cement deep mixing method has been used to improve soft clayey soils under embankment loading conditions. A compacted granular fill layer, or a geosynthetic reinforcement layer, is placed over the top of soil‐cement deep mixed (DM) columns, to reduce differential settlement between DM treated soil and the surrounding untreated soil, which in turn increases the embankment stability. Typically, in the conventional DM treatments, the soil‐cement columns are closely spaced, indicating large area replacement ratios in the construction projects. Such practice could increase construction costs substantially. In this research, a new type of DM column called T‐shaped DM or simply TDM column was designed and used as an alternative to large area replacement ratio of DM columns used in the field. Unlike the conventional column, the cross‐section of the new column varies along the installation depth. Large amounts of cement‐slurry is injected and thoroughly mixed with the in‐situ shallow soil by utilizing specially designed mixing blades. At the deeper depths, DM treatments are only applied to smaller diameter columns, thereby forming a column with a large diameter near the ground surface and a smaller size diameter at larger depths. Field trial tests were conducted to investigate the performance of the soft ground improvements by TDM columns under the embankment loading. For comparisons, the performance of the conventional DM column treated soft ground under similar embankment loading is presented. The differences in quality control studies and in‐situ plate loading tests on TDM and conventional DM columns are discussed. Under field embankment loading conditions, stress concentration ratio, excess pore water pressures generated in the soft clays, total monitored settlements, and lateral soil displacements near embankment toes are analyzed and discussed for both treatments. It is concluded that the TDM method has resulted in considerable advantages over the conventional DM method by both mitigating settlements and enhancing the performance of the embankments while lowering construction costs.

Select this Article		Reliability Analysis of Rock Wedge Stability — A Knowledge‐Based Clustered Partitioning (KCP) Approach Ya‐Fen Lee, Yun‐Yao Chi, C. Hsein Juang, F. ASCE, and Der‐Her Lee Journal of Geotechnical and Geoenvironmental Engineering doi:http://dx.doi.org/10.1061/(ASCE)GT.1943-5606.0000618 Posted ahead of print 17 August 2011 Full Text: \| Download PDF
	+ -	Show Abstract In this paper a knowledge‐based clustered partitioning technique is developed for determining reliability index and failure probability of rock wedge. Here, the Hasofer and Lind's reliability index is analyzed and the optimization is carried out using a knowledge‐based clustered partitioning (KCP) technique. The reliability index computed with this KCP technique is compared with those using other approaches such as the Excel Solver‐based method. The new technique for determining the reliability index involves a global search method and is found effective and efficient. Reliability analysis with this KCP technique is then used to examine the influence of parameter uncertainties and correlations among the parameters on the failure probability of rock wedges. Significant findings are derived from the sensitivity and parametric analysis.