Journal of Geotechnical & Geoenvironmental Engineering

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December 2007

Volume 133, Issue 12, pp. 1483-1640

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Performance of a Geogrid-Reinforced and Pile-Supported Highway Embankment over Soft Clay: Case Study

H. L. Liu, Charles W. W. Ng, M.ASCE, and K. Fei

J. Geotech. Geoenviron. Eng. 133, 1483 (2007); http://dx.doi.org/10.1061/(ASCE)1090-0241(2007)133:12(1483) (11 pages) | Cited 13 times

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This paper describes a case history of a geogrid-reinforced and pile-supported (GRPS) highway embankment with a low area improvement ratio of 8.7%. Field monitored data from contact pressures acting on the pile and soil surfaces, pore-water pressures, settlements and lateral displacements are reported and discussed. The case history is backanalyzed by carrying out three-dimensional (3D) fully coupled finite-element analysis. The measured and computed results are compared and discussed. Based on the field observations of contact stresses and pore-water pressures and the numerical simulations of the embankment construction, it is clear that there was a significant load transfer from the soil to the piles due to soil arching. The measured contact pressure acting on the pile was about 14 times higher than that acting on the soil located between the piles. This transfer greatly reduced excess positive pore water pressures induced in the soft silty clay. The measured excess pore water pressure ratio mathmax in the soft silty clay was only about 0.3. For embankment higher than 2.5 m, predictions of stress reduction ratio based on two common existing design methods are consistent with the measured values and the 3D numerical simulations. During the construction of the piled embankment, the measured lateral displacement–settlement ratio was only about 0.2. This suggests that the use of GRPS system can reduce lateral displacements and enhance the stability of an embankment significantly.

Load Testing and Settlement Prediction of Shallow Foundation

J. Brian Anderson, M.ASCE, F. C. Townsend, ASCE, and L. Rahelison

J. Geotech. Geoenviron. Eng. 133, 1494 (2007); http://dx.doi.org/10.1061/(ASCE)1090-0241(2007)133:12(1494) (9 pages) | Cited 4 times

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The purpose of this study was to critically examine insitu test methods as a means for predicting settlement of shallow foundations. Accordingly, a 1.8 m (6 ft) diameter concrete footing was statically load tested. Prior to construction, insitu [standard penetration test (SPT), cone penetration test (CPT), dilatometer (DMT), and pressuremeter (PMT)] and laboratory tests were performed to determine engineering properties of the soil. Predictions of the footing settlement were made by traditional as well as finite element methods. The results of the static load test showed settlements were over predicted by all methods. However, the traditional methods provided reasonable settlement estimates using either SPT-N or back computed CPT(N) as input. Finite element analyses using either DMT or CPT derived input parameters provided reasonable settlement estimates. Finite element analyses using SPT or PMT derived input parameters provided poor settlement estimates. The Mohr–Coulomb (elastoplastic) model, accounting for overconsolidation, provided better estimates than the hardening soil (hyperbolic-cap) model for all insitu test derived parameters.

Support Mechanisms of Rammed Aggregate Piers. I: Experimental Results

David J. White, A.M.ASCE, Ha T. V. Pham, A.M.ASCE, and Kenneth K. Hoevelkamp, A.M.ASCE

J. Geotech. Geoenviron. Eng. 133, 1503 (2007); http://dx.doi.org/10.1061/(ASCE)1090-0241(2007)133:12(1503) (9 pages) | Cited 5 times

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This paper is the first of a two-part series investigating the mechanical behavior of rammed aggregate pier (RAP) groups supporting isolated rigid footings. The first paper presents the experimental test results from instrumented load tests performed on two different 2.3 m square reinforced concrete footings supported by four 0.76 m diameter RAPs of two different pier lengths—2.8 and 5.1 m. Comparisons are made to load tests performed on three isolated RAPs of the same diameter and lengths. Instrumentation consisted of total stress cells, inclinometers, and tell-tale reference plates. Soil conditions at the test site were evaluated using various in situ testing techniques and consist of relatively uniform soft alluvial clay overlain by a 1-m-thick desiccated layer. Interpretations of the test results focused on load-deformation behaviors of the isolated piers and pier groups, group efficiencies in terms of settlement and bearing capacity, stress concentrations as a function of applied load at the top of the piers, and stress transfer with depth.

Support Mechanisms of Rammed Aggregate Piers. II: Numerical Analyses

Ha T. V. Pham, A.M.ASCE and David J. White, A.M.ASCE

J. Geotech. Geoenviron. Eng. 133, 1512 (2007); http://dx.doi.org/10.1061/(ASCE)1090-0241(2007)133:12(1512) (10 pages) | Cited 3 times

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This paper is the second of a two-part series describing an investigation of the mechanical behavior of rammed aggregate piers in supporting rigid square footings. In this paper, the performances of two pier-supported footings and three isolated piers during compressive load tests were simulated using an axisymmetric finite element model and compared to experimental data. A hardening-soil constitutive model with parameters estimated from in situ and laboratory tests was used to characterize the constitutive behaviors of the pier material and the matrix soil. Pier groups were modeled as unit cells with the tributary area determined from the center-to-center spacing. Cavity expansion modeling was used to simulate the pier installation process. Verifications of the numerical model were carried out by comparing the numerical results with the data obtained from full-scale, instrumented load tests. Interpretation of the numerical results focused on the load-deformation behavior, group effect, stress concentration ratio, and the development of stresses in the matrix soil. The distributions of vertical stress underneath the pier-supported footings are also characterized.

Yielding Pressure of Spread Footing above Multiple Voids

Makoto Kiyosumi, Osamu Kusakabe, Masatoshi Ohuchi, and Fang Le Peng

J. Geotech. Geoenviron. Eng. 133, 1522 (2007); http://dx.doi.org/10.1061/(ASCE)1090-0241(2007)133:12(1522) (10 pages) | Cited 1 time

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The effect of multiple voids on the yielding pressure of strip footing was numerically investigated by a two-dimensional plane strain finite-element method analysis. The results indicated that the failure zone developed mainly towards the nearest void from the footing and did not generally extend to the other voids, and the failure zone was narrower and smaller than that of the no-void ground, resulting in smaller yielding pressure. A practical calculation formula was developed for estimating the yielding pressure of strip footing above multiple voids.

Factors Controlling Instability of Homogeneous Soil Slopes under Rainfall

H. Rahardjo, T. H. Ong, R. B. Rezaur, and E. C. Leong

J. Geotech. Geoenviron. Eng. 133, 1532 (2007); http://dx.doi.org/10.1061/(ASCE)1090-0241(2007)133:12(1532) (12 pages) | Cited 15 times

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Rainfall-induced slope failure is a common geotechnical problem in the tropics where residual soils are abundant. Although the significance of rainwater infiltration in causing landslides is widely recognized, there have been different conclusions as to the relative roles of antecedent rainfall to landslides. The relative importance of soil properties, rainfall intensity, initial water table location and slope geometry in inducing instability of a homogenous soil slope under different rainfall was investigated through a series of parametric studies. Soil properties and rainfall intensity were found to be the primary factors controlling the instability of slopes due to rainfall, while the initial water table location and slope geometry only played a secondary role. The results from the parametric studies also indicated that for a given rainfall duration, there was a threshold rainfall intensity which would produce the global minimum factor of safety. Attempts have also been made to relate the findings from this study to those observed in the field by other researchers. Results of this parametric study clearly indicated that the significance of antecedent rainfall depends on soil permeability.

Three-Dimensional Asymmetrical Slope Stability Analysis Extension of Bishop’s, Janbu’s, and Morgenstern–Price’s Techniques

Y. M. Cheng and C. J. Yip

J. Geotech. Geoenviron. Eng. 133, 1544 (2007); http://dx.doi.org/10.1061/(ASCE)1090-0241(2007)133:12(1544) (12 pages) | Cited 3 times

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Most existing three-dimensional (3D) slope stability analysis methods are based on simple extensions of corresponding two-dimensional (2D) methods of analysis and a plane of symmetry or direction of slide is implicitly assumed. In this paper, 3D asymmetric slope stability models based on extensions of Bishop’s simplified, Janbu’s simplified, and Morgenstern–Price’s methods are developed. Under these new formulations, the direction of slide is unique and is determined from 3D force/moment equilibrium. Results from the new formulations are similar to the classical methods in normal cases but are numerically stable under transverse load. Further, the writers demonstrate that the present formulation is actually equivalent to the axes rotation formulation by Jiang and Yamagami but is much more convenient to be used for general problems. The writers have also discovered some inherent limitations of 3D limit equilibrium analysis which are absent in the corresponding 2D analysis.

Interpretation of Secant Shear Modulus Degradation Characteristics from Pressuremeter Tests

Yu Wang, M.ASCE and Thomas D. O’Rourke, M.ASCE

J. Geotech. Geoenviron. Eng. 133, 1556 (2007); http://dx.doi.org/10.1061/(ASCE)1090-0241(2007)133:12(1556) (11 pages)

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Nonlinear shear modulus degradation characteristics are of interest in many geotechnical engineering applications, such as ground deformation caused by seismic shaking and deep excavations in clay, weathered rock, and stabilized soil. This paper presents an approach to derive the secant shear modulus degradation characteristics from in situ pressuremeter tests, which is based on a digital filter algorithm. The algorithm is described, and data preparation procedures are presented. Use of the algorithm is illustrated by means of pressuremeter data for soils stabilized with deep mixing methods on the Boston central artery/tunnel (CA/T). The nonlinear secant shear modulus degradation characteristics from the digital filter approach are shown to be in good agreement with those from the curve fitting and transformed-strain approaches. They also compare favorably with the results of other in situ and laboratory tests performed in conjunction with the CA/T stabilized soils. The algorithm is implemented by a 26-line MATLAB code in an appendix of the paper.

Calibration of Soil Constitutive Models with Spatially Varying Parameters

Amy L. Rechenmacher, A.M.ASCE and Zenon Medina-Cetina, S.M.ASCE

J. Geotech. Geoenviron. Eng. 133, 1567 (2007); http://dx.doi.org/10.1061/(ASCE)1090-0241(2007)133:12(1567) (10 pages) | Cited 6 times

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Soil constitutive models are frequently calibrated from laboratory tests that utilize global boundary measurements, which necessarily relegate soil response to that of a homogenized equivalent medium. This paper demonstrates the applicability of advanced experimental technologies to enhance the state of model-based predictions in soil mechanics by taking into account the possibility of material heterogeneity during model calibration. By utilizing the full-field displacement measurement technique of three-dimensional digital image correlation, displacements of the surfaces of deforming triaxial sand specimens are measured throughout deformation. These displacements are assimilated into finite-element (FE) models of the test specimen through solution of an inverse problem. During optimization, in which the difference between measured and predicted displacements across the specimen surface form the basis for the objective function, model parameters are allowed to vary spatially throughout the specimen volume. FE models allowing three different levels of spatial variability are tested. Results indicate that accommodating consideration of material heterogeneity during calibration leads to more accurate predictions of global stress-strain behavior that are more faithful to observed full-field response.

Use of In Situ Air Flow Measurements to Study Permeability in Cracked Clay Soils

Tony Wells, Stephen Fityus, and David W. Smith

J. Geotech. Geoenviron. Eng. 133, 1577 (2007); http://dx.doi.org/10.1061/(ASCE)1090-0241(2007)133:12(1577) (10 pages)

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The work describes in situ measurements of crack induced permeability as a function of depth, (down to ∼ 1.75 m), in clay soils at two field sites, using the gas flow technique described in an earlier study. The gas flow response to applied pressure was found to exhibit a significant nonlinearity at all depths indicating non-Darcian flow despite the fact that the flow was likely to be well within the laminar flow regime. Application of three-dimensional finite-element models to describe the gas flow revealed that the nonlinearity is likely to be an intrinsic behavior related to the soil-gas flow interaction. The Forchheimer compressible flow equation successfully simulated the behavior at all depths. The viscous and inertial permeability parameters obtained from this analysis showed a wide range of values which were closely correlated to the pore-water content of the soil medium, clearly showing the influence of ped swelling on the contraction of macrovoid channels in the structured clay soil.

Lactate Transport in Soil by DC Fields

Xingzhi Wu, Akram N. Alshawabkeh, David B. Gent, Steven L. Larson, and Jeffery L. Davis

J. Geotech. Geoenviron. Eng. 133, 1587 (2007); http://dx.doi.org/10.1061/(ASCE)1090-0241(2007)133:12(1587) (10 pages) | Cited 5 times

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Electrokinetic injection of lactate, a negatively charged biodegradable organic, in homogeneous soils is evaluated. Net lactate migration rate on the order of 5 cm2/V day is measured in sand from cathode towards the anode. The ionic injection in sand was dependent on current density; however, the increase in electric current did not result in an equivalent increase in lactate transport due to development of an appreciable electroosmotic (EO) flow from the anode to the cathode. While high EO flow (ke on the order 10−6 to 10−5 cm2/V s) occurred in clay samples, ion migration from cathode to anode is the dominant transport process under relatively high current density (5.3 A/m2 in this study) and can be used as an effective transport mechanism for negatively charged additives. An effective lactate reactive transport rate of more than 3 cm/d (under 1 V/cm) can be achieved in clays, which is at least two orders of magnitude greater than hydraulic injection under unit hydraulic gradient. Even though lactate concentrations in the clay were below 10% of the boundary value due to biological transformation, these concentrations (few 100 s mg/L) are high enough to maintain microbial activities capable of degrading organic contaminants. At the same time, control experiments showed that, while lactate adsorption was negligible, hydraulic injection under a unit gradient was ineffective because of the low hydraulic conductivity of clay and the biodegradation of lactate.

Time Domain Reflectometry Surface Reflections for Dielectric Constant in Highly Conductive Soils

Renpeng Chen, Vincent P. Drnevich, F.ASCE, Xiong Yu, M.ASCE, Robert L. Nowack, and Yunmin Chen

J. Geotech. Geoenviron. Eng. 133, 1597 (2007); http://dx.doi.org/10.1061/(ASCE)1090-0241(2007)133:12(1597) (12 pages) | Cited 3 times

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This paper presents a model-based approach to determine dielectric constants from time domain reflectometry (TDR) measurement in highly conductive soils. It makes use of information contained in the TDR signal from the reflection at the surface of the soil rather than the reflection from the end of the probe. The TDR method is widely used to determine the volumetric water content of soils. Commonly used information from the TDR signals includes the apparent dielectric constant and the electrical conductivity. The apparent dielectric constant is generally measured by analyzing the travel time of electromagnetic waves reflected from the end of the soil probe. In soils with high electrical conductivities, the attenuation of the signal can eliminate the reflection from the end of the probe, which limits the application of TDR to these materials. A simplified frequency-independent dielectric model is utilized to invert the dielectric constant from the reflected signals at the soil surface. Results indicate that the dielectric constant can be determined with reasonable accuracy by the proposed approach for soils with high electrical conductivity, where the conventional travel time analysis fails due to significant signal attenuation.

In-Place Stabilization of Pond Ash Deposits by Hydrated Lime Columns

Sudeep Kumar Chand and Chillara Subbarao

J. Geotech. Geoenviron. Eng. 133, 1609 (2007); http://dx.doi.org/10.1061/(ASCE)1090-0241(2007)133:12(1609) (8 pages) | Cited 1 time

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Abandoned coal ash ponds cover up vast stretches of precious land and cause environmental problems. Application of suitable in situ stabilization methods may bring about improvement in the geotechnical properties of the ash deposit as a whole, converting it to a usable site. In this study, a technique of in-place stabilization by hydrated lime columns was applied to large-scale laboratory models of ash ponds. Samples collected from different radial distances and different depths of the ash deposit were tested to study the improvements in the water content, dry density, particle size distribution, unconfined compressive strength, pH, hydraulic conductivity, and leachate characteristics over a period of one year. The in-place stabilization by lime column technique has been found effective in increasing the unconfined compressive strength and reducing hydraulic conductivity of pond ash deposits in addition to modifying other geotechnical parameters. The method has also proved to be useful in reducing the contamination potential of the ash leachates, thus mitigating the adverse environmental effects of ash deposits.
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Interface Electric Resistance of Electroosmotic Consolidation

Yan-Feng Zhuang and Zhao Wang

J. Geotech. Geoenviron. Eng. 133, 1617 (2007); http://dx.doi.org/10.1061/(ASCE)1090-0241(2007)133:12(1617) (5 pages) | Cited 1 time

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There will be transition zones of electric current near the electrodes, if the electric conductive area of electrodes is smaller than that of soil. Electroosmosis tests show that the electric current in the transition zones follows a complicated two-dimensional path, while the electric current outside these zones is approximately one dimension. The thickness of transition zones is potty compared to the whole thickness of soil between anodes and cathodes. Conception of interface resistance on zero thickness interfaces, which is a simplified expression for finite thickness transition zones, is presented in this paper to simplify the two-dimensional problem within the transition zones into one dimension. Studies show that the interface electric resistance is inversely proportional to the ratio of electric conductive areas between electrodes and soil. A brief formula is deduced to predict the in situ interface electrical resistance, which presents a more accurate estimation of electric current and energy consumption to the design of electroosmotic consolidation engineering.

Screw Conveyor Device for Laboratory Tests on Conditioned Soil for EPB Tunneling Operations

Daniele Peila, Claudio Oggeri, and Raffaele Vinai

J. Geotech. Geoenviron. Eng. 133, 1622 (2007); http://dx.doi.org/10.1061/(ASCE)1090-0241(2007)133:12(1622) (4 pages) | Cited 5 times

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Earth pressure balanced (EPB) full face tunneling machines have experienced a remarkable increase in the number of applications throughout the world due to both mechanical developments and a more effective use of additives to condition the ground. Conditioning modifies the mechanical and hydraulic properties of a soil by making it suitable for the pressure control in the bulk chamber and extraction with the screw conveyor. The extraction system plays a fundamental role during the EPB operations particularly for a correct application of the face pressure. Despite the extensive use of the EPB technique, little knowledge exists concerning the understanding of the behavior of conditioned soil, particularly for noncohesive ground (sand and gravel). This paper presents and describes a prototype laboratory device, which simulates the extraction of the ground from a pressurized tank with a screw conveyor. The results of a preliminary test program carried out on a medium sized sand show that the prototype device is efficient in verifying the effects of foam for an optimal use in EPB conditioning.

Characterization of Fines Produced by Sand Crushing

Julio R. Valdes, M.ASCE and Eren Koprulu

J. Geotech. Geoenviron. Eng. 133, 1626 (2007); http://dx.doi.org/10.1061/(ASCE)1090-0241(2007)133:12(1626) (5 pages)

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Sand particle crushing generates coarse fragments with size d ≥ 75 μm and fine fragments, i.e., “fines,” with size d<75 μm. Yet, postcrushing fines are seldom characterized due to testing constraints. An experimental study was conducted to examine the size distribution evolution of fine fragments generated by crushing two uniform sands with contrasting degrees of mineral composition heterogeneity, in one-dimensional compression. The determination of fine fragment sizes was made possible by using a particle size analyzer that employs a small sample. The results indicate that the degree of mineral composition heterogeneity affects the load–deformation behavior of crushing sands and the resulting amounts and size distribution evolutions of the produced coarse and fine fragments. In particular, the trends gathered suggest that fines generation occurs by abrasion of parent particles, coarse fragment breakage, and subsequent breakage of fine fragments with sizes larger than the comminution limit.
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Discussion of “Performance of a Cantilever Retaining Wall” by Joseph G. Bentler and Joseph F. Labuz

William J. Neely, M.ASCE, P.E.

J. Geotech. Geoenviron. Eng. 133, 1631 (2007); http://dx.doi.org/10.1061/(ASCE)1090-0241(2007)133:12(1631) (3 pages) | Cited 1 time

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Closure to “Performance of a Cantilever Retaining Wall” by Joseph G. Bentler and Joseph F. Labuz

Joseph G. Bentler, A.M.ASCE and Joseph F. Labuz, M.ASCE

J. Geotech. Geoenviron. Eng. 133, 1633 (2007); http://dx.doi.org/10.1061/(ASCE)1090-0241(2007)133:12(1633) (2 pages)

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Closure to “Behavior of a Fiber-Reinforced Bentonite at Large Shear Displacements” by Michéle Dal Toé Casagrande, Matthew Richard Coop, and Nilo Cesar Consoli

Michéle Dal Toé Casagrande, Matthew Richard Coop, and Nilo Cesar Consoli

J. Geotech. Geoenviron. Eng. 133, 1635 (2007); http://dx.doi.org/10.1061/(ASCE)1090-0241(2007)133:12(1635) (1 page)

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J. Geotech. Geoenviron. Eng. 133, 1637 (2007); http://dx.doi.org/10.1061/(ASCE)1090-0241(2007)133:12(1637) (4 pages)

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