Geotechnical Frontiers 2025: Geotechnical Infrastructure

Earthquakes are a major concern for the stability and performance of natural slopes, man-made excavations, and other earth structures such as dams and embankments. Conventionally, pseudo-static analysis and Newmark-type procedures are used for assessing the seismic performance of slopes from where displacement estimates are obtained. Limit equilibrium methods utilize a seismic coefficient based on a code or guidelines presented in the technical literature. This paper presents the results of a series of site response analyses using the computer program FLAC^2D carried out for a steep 300 m high rock slope reinforced with multiple anchors. The results of the site response simulations are used to define a site-specific seismic coefficient for use in limit equilibrium pseudo-static analyses. The paper also compares the results of this study with available data from similar ground conditions.

Levees are vital for protecting communities from flooding, and their failure can have catastrophic consequences. Factors like overtopping, slope instability, settlement, seepage, and erosion can lead to levee failure, with seepage and erosion gradually compromising structural integrity and causing breaches. Soil piping, resulting from prolonged under-seepage, has been a significant cause of failure, especially in levees on highly permeable soil deposits. Traditionally, several remediation methods are employed to address this, one of which is the use of pervious toe trenches that can reduce the exit gradient significantly, thereby avoiding the piping phenomenon. This study critically evaluates using steel slag instead of sand as fill material in drainage trenches to enhance the sustainability of remediation efforts. Focusing on a levee near Libertyville, Illinois, USA, along the Des Plaines River, the study investigates the application of steel slag to prevent potential under-seepage. Steady-state seepage analysis revealed a high exit gradient of 2.5, indicating a risk of piping under prolonged high water levels. Introducing a pervious toe trench filled with high permeability materials is recommended, and the use of basic oxygen furnace (BOF) slag instead of traditional sand is critically evaluated in this study, owing to its high permeability and specific gravity. Although BOF slag has lower permeability compared to sand, the slag-filled trench demonstrated a significant improvement in the factor of safety (FOS) against piping failure. The FOS for the BOF slag-filled trench was 1.4 under normal flood conditions and 1.2 under high flood conditions, compared to 0.6 and 0.4, respectively, for the scenario without any trench. The high specific gravity of BOF slag enables it to withstand higher gradients, making it a safer choice for trench fill material to prevent piping failure. Further evaluation of technical and environmental considerations, such as gradation requirements, toxicity characteristics, and the effects of mineral carbonation, indicated that BOF slag is a suitable replacement for sand in drainage trenches.

Slope stability is a critical concern in civil engineering, especially in excavation and trenching projects where failure modes significantly challenge this stability. Slope failures and landslides occur due to reduced effective stress between soil particles caused by soil saturation and increased weight, leading to reduced friction and heightened susceptibility to slope instability. Traditionally, calculations assume constant shear strength parameters for each soil layer. However, the presence of soluble pollutants alters this assumption, affecting soil cohesion, friction angle, and modifying failure criteria. This research aims to investigate the impacts of fertilizer, acid rain, and landfill leachate on the cohesion and friction angle of natural soils exposed to these contaminants, and their effects on factors of safety of slopes and excavations. By exploring the effects of pollutants on soil behavior and stability, this research seeks to enhance understanding and management of slope stability in geotechnical engineering practice, offering valuable insights for designing and implementing effective control measures to mitigate the risks associated with slope instability in construction and excavation projects.

Detecting seepage in earthen dams is crucial for ensuring their structural integrity and preventing potential hazards. This study proposes a novel, non-destructive method employing a thermal infrared camera to detect seepage and to understand the thermal color contrast for seepage-induced surface erosion. For a given camera, operating parameters, i.e., atmospheric temperature, humidity, and emissivity of the materials, a series of laboratory experiments are performed on model earthen dams for varying seepage rates, ranging from nominal to significant seepage rates. The study aims to understand the seepage patterns and role of the temperature gradient in monitoring the stability of earthen dams under diverse seepage conditions, facilitating improved risk assessment and management strategies for dam infrastructure. Additionally, advanced temperature matrix analysis is performed to correlate temperature differences with the seepage rates adopted in the study. Finally, some insights on integrating the current findings with the rapidly advancing drone techniques in the early detection of seepage-related anomalies across various seepage scenarios are provided.

Changing precipitation patterns due to climate change have increased the frequency and intensity of extreme weather events, causing widespread slope instability issues triggered by heavy rainfall. For instance, a storm in California in February 2024 triggered 475 mudslides in Los Angeles, damaging nearly two dozen houses. This highlights the need to study the effects of rainfall characteristics and soil conditions on the stability of unsaturated slopes. This study examined the combined impact of rainfall characteristics and initial soil conditions on unsaturated clay slopes. Using a statistical analysis for the optimal experimental design, a full factorial approach required 360 numerical models, later optimized to 11 finite element models developed in SEEP/W, SIGMA/W, and SLOPE/W of GeoStudio. The factor of safety of the slope was found to depend on the void ratio and rainfall characteristics. Seepage velocity and deformation occurring in the slope was found to be a function of the intensity of rainfall and the initial void ratio of the soil. Rainwater infiltration indicated a decrease in the suction strength of the unsaturated slope leading to a decrease in the shear strength of the soil resulting in lower factor of safety and potential instability issues.

This study presents a comprehensive analysis of factors contributing to landslides in North Dakota by comparing traditional interpretation techniques and multivariate logistic regression analysis. A total of 66,894 landslides were mapped and compared with 68,395 randomly selected stable areas to assess landslide susceptibility. Logistic regression and traditional analyses were conducted to evaluate the influence of geological formation, land cover, slope angle, precipitation, snowfall, electrical conductivity, and sodium absorption ratio on landslide occurrence. Performance was assessed with varying data set sizes, highlighting the impact on model accuracy and robustness. Probabilistic contours were developed to capture the combined effects of key factors on landslide probability, with the logistic regression model identifying precipitation, snowfall, and slope as the most significant predictors. The model highlighted the increased landslide risk posed by the interaction of severe snowfall and steep slopes. It also demonstrated consistency and reliability even with smaller data sets, offering detailed spatial visualizations of landslide likelihood. When integrated with a map engine, the model enhanced spatial analysis, allowing for intuitive geographic representations that can provide localized insights and improve decision-making in landslide susceptibility assessments, complementing traditional methods.

Highway embankments constructed from problematic soils frequently experience distress due to cyclic environmental stressors. The strains are further aggravated by imminent changes in climatic conditions like extreme rainfall and drought. Additional pressure on transportation infrastructure systems threatens their long-term serviceability. In light of this, the paper discusses two case studies of embankment slope failure in Houston, Texas. The first slope is located near IH610, where a section of the slope beside the highway, even after multiple rehabilitation efforts, has failed. The study shows that removing trees along the slope, critical slope angle, and lack of proper drainage caused the slope to fail. The following case study is about another slope beside route UA90 near Buffalo Bayou. Here, the historical increase in the flood level of the bayou has caused the toe erosion of the slope, which resulted in the progressive failure leading to a total collapse of the entire slope. The case studies provide the details of the site investigation, laboratory characterization, and use of climatic data to understand the reasons for slope failure. Additionally, potential mitigation measures are also discussed, which are validated using different finite element-based models to ensure that the rehabilitated slopes are resilient to future climatic events and could lead to long-term serviceability of the transportation infrastructure.

This study aims to use a multi-instrument remote sensing approach leveraging freely accessible Sentinel-1 SAR and multispectral data to monitor and analyze deformation and factors contributing to the deterioration of the Lake Tholocco Dam and levee in Alabama. Sentinel-1 InSAR data, spanning from April 2016 to July 2023, were processed through the COMET-LiCSAR platform to measure surface deformation. The study revealed a maximum subsidence rate of 8 mm/year near the Lake Tholocco Dam, with significant deformation along Johnston Road at 7 mm/year. Our research uncovered a strong correlation between levee deformation and hydrometeorological factors. Time series analysis of InSAR displacements, precipitation, soil moisture, and temperature data demonstrated that the levee crest rises with increased rainfall and settles during drier periods, a cyclical behavior superimposed on a long-term settlement trend attributed to the consolidation of the clay core. Additionally, the study highlighted the potential influence of vegetation cover on deformation patterns and the accuracy of Sentinel-1 InSAR measurements to further assess the reliability of satellite-based measurements. This integrated approach shows promise in providing a comprehensive framework for assessing levee integrity and predicting potential failures. However, challenges persist, particularly in vegetated areas like Dale County, where future advancements, such as the launch of satellites like NiSAR, are expected to improve monitoring capabilities.

Adapting geotechnical infrastructure requires careful consideration of the impact of climatic extremes, requiring a multidisciplinary approach that integrates geotechnical engineering, hydrology, and climate science. This study investigates the probability of failure of an earthen levee considering the variability in flood hydrographs and the hydraulic properties of unsaturated soils. A numerical modeling framework was employed to evaluate the impact of coastal processes on the probability of failure of earthen levees due to piping at the toe. To account for variability in hydraulic loading conditions, flood hydrographs for several scenarios are simulated and applied in a transient seepage and limit equilibrium slope stability model. The variability in hydraulic properties of unsaturated soils was considered by generating random values for the fitting parameters of the van Genuchten soil water retention curve (SWRC) model. The results indicate that higher initial water levels lead to increased hydraulic exit gradients, higher outflow water rates, and reduced safety factors. Fragility curves constructed from the data reveal that the probability of failure due to piping increases with higher demand parameters, such as peak intensity and total volume, and is modulated by the duration of hydrograph events.

Embankment dams are essential and costly water management infrastructure. The evaluation of the safety of both new and existing embankment dams presents special and unique problems. This study presents the results of settlement analysis conducted for the constructability of earthen embankment dams for the Papio-Missouri River Natural Resources District (P-MRNRD) in Eastern Nebraska in USA due to consolidation of underlying alluvium and loess deposits under the weight of the dam embankment. Pre-design settlement predictions will be presented, as actual settlement measurements obtained during construction. The objective of the study is to develop the risk analysis methodology for the consolidation settlement of dams. This requires the development of reliability models involving the establishment of serviceability limit state functions. The most important part of this study is the development of statistical models and distribution for consolidation settlement of dams. Reliability indices are determined for consolidation settlement of the earthen embankment dams assigned in this study.

Embankments are crucial components of transportation and flood defense infrastructure, yet those constructed from clays are prone to weather-driven deterioration processes, resulting in gradual loss of hydromechanical performance and potentially severe failures. This paper documents a study aimed to forecast the time to failure of aging clay embankments supporting transportation infrastructure. In this study, a multi-phase numerical modeling approach was used to simulate the long-term, weather-driven hydromechanical behavior of clay embankments of well-documented failure case studies. Numerical models were developed for 34 case studies, and simulations predicted the time to failure due to progressive deterioration. This modeling approach proved efficient in producing data necessary for improving infrastructure asset management. Based on the observations from the numerical results, it is recommended that a Factor of Safety (FoS) target against weather-driven shallow slides is introduced in evaluating the stability of existing embankment slopes and new embankment slopes. An FoS of 1.1–1.2 may be used for existing embankments considering the temporary nature of the conditions causing shallow slides. For new designs, an FoS of 1.3 may be recommended.

Drought is a common natural phenomenon that can significantly reduce the water resources stored in dams. Prolonged drought conditions, lasting several months or years, gradually lower dam water levels, thereby altering the mechanical behavior of dam slopes under seismic loading during earthquakes. This paper investigates the dynamic behavior of a clay-core rockfill dam when its reservoir is empty. Specifically, it addresses gaps in geotechnical research related to the influence of seismic impulse direction, dam geometry, support conditions, and proximity to the earthquake epicenter on the dam’s dynamic response. To bridge these gaps, this study analyzes the response of a rockfill dam to near- and far-field seismic events, considering different directional impulses. The analysis is carried out using GTS Midas software, with random vibration employed to simulate the dam’s behavior under actual seismic conditions. A range of valley shapes is simulated, and detailed comparisons are made between 2D and 3D models. Additionally, the study explores the seismic response of embankments under various earthquakes and evaluates the role of boundary support conditions. The findings underscore the importance of modeling the actual foundation, including mountainous abutments, when simulating permanent settlements caused by earthquakes. The results also highlight that near-field shocks induce more severe dynamic responses compared to far-field quakes, with vertical impulses yielding the highest magnification factors. Meanwhile, longitudinal shocks result in the greatest permanent settlements, emphasizing the necessity of 3D dynamic modeling for accurate analysis of rockfill dams.

Soft soil is prevalent worldwide, especially in coastal regions, making it crucial to thoroughly understand its behaviour under cyclic loading to ensure the proper design of railway substructures. The operation of heavy freight trains induces a notable increase in excess pore water pressure (EPWP) and plastic strain, if not adequately dissipated or drained, which can temporarily reduce the bearing capacity, potentially leading to severe damage to rail infrastructure such as mud pumping, ballast degradation, and excessive settlement. This research delves into the behaviour of soft soils under undrained cyclic loading, with different cyclic stress ratios (CSR), through a series of cyclic tests. The Modified Cam Clay (MCC) model is extended to predict soil response under undrained cyclic loading by incorporating a dynamic yield surface during cyclic loading. Results reveal that beyond a critical cyclic stress ratio (CSRc), both EPWP and axial strain experience a rapid escalation after a certain number of cycles. Moisture and fine particles migrate upwards toward the specimen’s top, contributing to soil softening and fluidization and leading to soil instability. The findings highlight the significant impact of drainage conditions via geosynthetics on soft soil subgrade stability under cyclic loads. The installation of vertical drains is shown to enhance radial drainage, facilitating the dissipation of EPWP, thereby enhancing soil stability. Geosynthetics are proven effective in mitigating fine particle migration and EPWP accumulation, thereby reducing the EPWP gradient and preventing mud pumping.

Column-supported embankments are regularly supported on rigid columns to accelerate construction when difficult subsoil conditions are encountered. Current simplified methodologies to evaluate global stability of CSEs violate several aspects of the fundamental physics associated with load transfer mechanisms and/or modes of column-failure. A simplified framework to assess the global stability of CSEs is proposed and compared with modified slope stability methods and numerical analyses. The complex changes in vertical stress within the reinforced zone are included in the assessment of lateral driving stresses applied in a strength-reduction limit-equilibrium technique to compute the factor of safety and the location of a critical slip surface. Predictions are compared with simplified methodologies proposed by others and numerical analyses for two hypothetical CSEs. The factors of safety and predicted critical slip surfaces are compared and discussed. Generally, the new simplified methodology provided the best agreement in terms of factor of safety and critical slip surface predictions with numerical analyses—which more faithfully captures the complex physics of the problem. The new framework is tractable and can be used by engineers to make physically meaningful, but computationally efficient, predictions.

Highway projects often entail the reconstruction or widening of embankments. The load induced by such new surcharge loads can cause undesired settlements in nearby preexisting structures. Current design practices attempt to control deformation in preexisting structures by limiting the design load, increasing the foundation bearing capacity, or constructing new structures far away from the influence zone of preexisting structures. The application of deformation barriers could be a cost-effective alternative to mitigate such induced settlements. The use of vertical barriers such as sheet-pile walls is a common solution to control settlement due to excavation; however, its applications have not been investigated for the case of mitigating settlement due to loading near preexisting structures (in the absence of excavation). This research investigates the effectiveness of installing a sheet-pile wall between the new construction (loaded side) and the existing structure (adjacent side) to reduce undesired settlements. We use a plane-strain finite-element numerical model to conduct a parametric study, assessing the influence of various factors such as depth of sheet-pile wall, depth of bedrock, and soil-sheet-pile wall interface friction on the settlement profile. Results show that the settlement profile is mainly controlled by the ratio of the sheet-pile wall depth to the bedrock depth and the interface friction between the wall and the soil. Based on this understating, we present a preliminary design chart that facilitates the selection of an appropriate sheet-pile wall depth to achieve the desired reduction in settlement on the adjacent side.

Located on the East Entrance Road in Yellowstone National Park, Wyoming, the approximately 1,500-ft long Pelican Creek Bridge Replacement Project was completed in 2020, replacing an existing 197-ft long bridge and associated causeway that spanned the Pelican Creek Valley. The project is located near the north shore of Yellowstone Lake. The new bridge provided the opportunity to remove the approximately 1,300-ft long causeway, which was located within and bisected the Pelican Creek wetlands. Removal of the causeway provided significant environmental benefits by reconnecting wetlands and restoration of natural channel migration of Pelican Creek. The bridge is 9 spans and founded on large diameter open-end pipe piles. The soils at the site consist of liquefiable alluvial and lacustrine deposits. The site is within the Yellowstone Caldera and is an area of high seismicity. A peer-reviewed site-specific dynamic soil response analysis was conducted for the project. The recommended seismic design response spectra were much lower than the AASHTO standard procedure spectra at short periods. The liquefaction analysis demonstrated that portions of the soil profile were potentially liquefiable when subjected to design-level ground motions, and soils at the abutments were susceptible to lateral spreading. Ground improvement was performed at the abutments to mitigate the ground failure hazards associated with lateral spreading and lateral flow. The foundations consist of 24-in. pipe piles at the abutments and 42-in. pipe piles at the interior bents. Final design geotechnical investigations consisted of 18 borings and six cone penetration test soundings performed in 2016. Static analysis methods were supplemented with full-scale dynamic and static pile load tests at the site. A dynamic load test was performed on two piles at the site in 1997, when other projects were being constructed in the area. A dynamic and static load test program was completed in 2017. Following a 38-day setup period, the static load test was performed. Interpretation of the load test results, along with construction testing requirements, yielded pile lengths shorter than those calculated using static analysis methods. The reduction in pile length and number of splices required to be field welded resulted in significant time and cost savings to the contract. Due to the relatively short construction season in Yellowstone National Park, generally May to October, the reduction in pile lengths eliminated 1 year from the construction schedule.

Numerous methodologies using empirical relationships have been developed for the design of load transfer platforms supporting earthen embankments over soft soils. Variations in modeling how the embankment overburden stresses are partially transferred to the stiff vertical elements supporting the embankment through soil arching will lead to differing imposed subgrade stresses calculated. Furthermore, variations of soil shear strengths considered in the analyses led to further discrepancy in results between the design methodologies. Limit equilibrium parametric analyses were performed for several of the existing methodologies for the design of load transfer platforms to identify the variation of embankment transfer efficiency between the models. This paper will present the results of the parametric analyses of the empirical relationships and provide recommendations for estimating imposed subgrade stress.

Full-scale tests on instrumented geosynthetic reinforced soil (GRS) piers were performed to investigate the bearing and deformation performance of lightweight aggregate and a poorly graded No. 57 stone backfill. Each pier was constructed with a height-to-width ratio of 2 and confined with segmental retaining blocks. The reinforcement was a woven polypropylene geotextile with 105 kN/m and 84 kN/m tensile strengths in the machine direction (MD) and cross-machine direction (CD), respectively, and vertically spaced 0.2 m. The applied load, vertical displacement of a footing at the top of pier, and the deflected shape of each pier were monitored during the tests. Results indicate the capacity and deformations of the lightweight aggregate backfilled pier meet recommended service limits and are about 40% of the load carried by the No. 57 stone pier at 1% vertical strain. Yielding of the lightweight aggregate pier is around 2% axial strain followed by aggregate crushing within the top third of the pier and a bearing capacity of about two-thirds of the No. 57 stone pier.

Increased climate stress presents unique design and maintenance challenges for ground anchors, which play a crucial role in highway and bridge slope stabilization. Distributed Fiber Optic Sensing (DFOS) technology is at the forefront of infrastructure performance monitoring of deformation and temperature over long distances at a high spatial resolution with high measurement frequencies. A novel DFOS-embedded steel strand tendon ground anchor was developed with embedded fiber optic cables for strain measurement throughout the anchor cross-section. This unique cable configuration enabled distributed strain sensing (DSS) along the steel strand tendon, internal grout, and external grout during pull-out testing and long-term. A full-scale field test with four 60-ft (18.3-m) ground anchors in mixed soil conditions was performed, with installation and pull-out testing in Antioch, CA. Varying grouting configurations were evaluated: with and without post-grouting. Two DFOS platforms, Optical Frequency Domain Reflectometry (OFDR) and Brillouin Time Domain Reflectometry (BOTDR), were demonstrated as suitable for ground anchor field monitoring. This novel approach enabled a detailed investigation of the tendon/grout/ground interaction mechanism and its effect on the strain transfer transition zone between the bonded and unbonded sections of the anchor. Looking forward, these findings will support a scalable and reliable field monitoring solution and ultimately advance the state of practice for resilient ground anchor design and construction.

An in situ test method has not been standardized for stiffness evaluation of full-depth reclaimed (FDR) and stabilized pavement materials. This paper reports a field evaluation of stabilized FDR pavement layers using a dynamic cone penetrometer (DCP), Clegg hammer, and two portable lightweight deflectometers (LWDs). The FDR layers were produced by pulverizing 356 mm of an existing asphalt pavement and stabilized with a combination of an asphalt emulsion and portland cement. The field tests were performed routinely over a period of 7 days to measure stiffness gain. After 7 days of curing, heavy weight deflectometer tests were conducted to estimate the FDR layers’ moduli. Nondestructive test methods were able to discriminate the quality of the different FDR layers but were not found effective in detecting stiffening trends during the curing period. The LWD_z yielded dynamic moduli that were 10 times greater than the LWD_D. The Clegg impact hammer test yielded increasing stiffness values until the third day of testing. The DCP test was more effective in tracking the early stiffness gain of FDR layers, although some DCP tests yielded refusal results (CBR greater than 100) at an early stage. A satisfactory correlation was not found between the field test results and the backcalculated moduli of the FDR layers that ranged between 620 and 1,310 MPa.

In seasonally frozen areas, accumulated infiltration causes the difference in frost heave during freezing and thawing seasons. Moisture content is the major contributing parameter for the subgrade modulus alteration in the Northeast region. With the onset of freezing, the non-freezing moisture content provides valuable insight about the subgrade soil behavior. As the thawing season is the most critical for pavement weakening, moisture content data could act as a performance indicator of the pavement. In order to gain a broader understanding of the subgrade moisture behavior during various seasons, we conducted instrumentation within the pavement subgrade in the Central New York region. We installed moisture sensors at varying depths to monitor the real-time moisture fluctuation over time. A weather station was also installed to capture the climatic data. The data collected from field instrumentation were used to derive descriptive statistical parameters such as histograms, quantile-quantile plots, distribution types, skewness, kurtosis, range, and standard deviation to quantify moisture variations at two distinct sites. The measured moisture content varied from 0.25 m³/m³ to 0.45 m³/m³ over the three-year monitoring period. In addition, the probability density function (PDF) plot revealed the frequency of the moisture data. Precipitation in terms of rainfall and snow-melt events contributed significantly to the temporal moisture variations. The same analysis was repeated for three cycles: 2019–2020, 2020–2021, and 2021–2022. Continued, extended monitoring will unveil the authentic response of the subgrade soil to climatic loading over an extended period which will assist the highway agencies in better maintenance of the road.

The laboratory measurement of resilient modulus involves measuring resilient strains at the surface of a specimen under repeated loads at various stress conditions. While Dual Linear Variable Differential Transformers (LVDTs) are commonly utilized in this testing, their effectiveness in measuring small strains, particularly with stiff geomaterials, is often met with challenges due to the accuracy of measurements. Recently, lasers have emerged as promising alternatives due to their versatility and precision in small strain measurements. Therefore, this study aims to introduce and compare the performance of LVDTs and laser-based measurements for determining resilient moduli of geomaterials. Repeated load triaxial tests were conducted on two types of soils at two different compaction energies. Subsequently, resilient moduli were determined considering the effects of multiple testing conditions such as confining pressure, deviatoric stress, and the number of pre-conditioning load cycles. Furthermore, a machine learning model was used to analyze and compare the results obtained from LVDTs and laser-based measurements. The results indicated that the resilient moduli are dependent on stress conditions and the initial compaction energy, while independent of the pre-conditioning load cycles. The LVDTs and laser-based measurements provided consistent values and trends for stiff and highly compacted materials, while for weak materials, the differences between these two techniques were up to 30%. Although there were differences in measurements, the machine learning analysis revealed that the nature of the LVDT and laser data set showed similarities in data patterns and computational matrices. Overall, the study offers a preliminary understanding of the potential performance of laser-based measurements and contributes to the development of testing techniques, particularly in the geotechnical engineering field.

This study focusses on the development of an aging index chart by artificially aging virgin asphalt samples in a variety of controlled oxidation environments and studying signature peaks in the spectrum using attenuated total reflectance test. Virgin asphalt binder samples have been aged artificially in the laboratory under varying pressure and temporal conditions that can be achieved in a pressure aging vessel (PAV). Artificially aged binder samples were examined to gauge changes in functional group intensities or stretching frequencies, indicating asphalt oxidation (aging). This data set serves as the foundation for developing an aging index chart, which will be used to determine the age of asphalt binder extracted from asphalt mixtures of demolition waste. The aging index is based on signature peaks in the spectrum obtained from ATR tests on the extracted binder.

Monitoring of earthen structures utilizing instrumentation (e.g., strain gauges, pore pressure transducers, and earthen pressure cells) has become essential in the long-term monitoring and identification of potential failure mechanisms of earthen structures. In some instances, to monitor the behavior of interest, earthen structures require a dense array of instrumentation which may not be economically feasible for some geotechnical applications. Within the geotechnical community, accelerometers have been heavily used in a variety of applications, including dynamic centrifuge testing, earthquake monitoring, pile driving analysis, and Intelligent Compaction. However, the utilization of a dense array of industrial-grade accelerometers may pose an economic barrier in order to monitor the soil behavior of interest. Within this study, a dense array of custom-fabricated accelerometers previously developed by the authors were installed along an earthen embankment to monitor the wave propagation behavior of the embankment during the soil compaction process. Industrial-grade accelerometers were also installed to verify the response of the custom-built accelerometers. This study discusses the installation process of these custom-built accelerometers and provides a side-by-side comparison between their acceleration and dynamic displacement responses relative to the industrial-grade accelerometers. Overall, the custom-built accelerometers were able to capture the same salient trends of wave propagation behavior of the earthen embankment relative to the industrial-grade accelerometers when subjected to real-world soil compaction conditions.

Balanced mix design (BMD) is a method of balancing cracking and rutting performances of an asphalt mix; thus, BMD is an improvement of the traditional Superpave method. In this study, mixes were designed using Superpave method and using virgin and recycled aggregates and Performance Grade asphalt binder (PG 64-22). Asphalt mixes were prepared using virgin aggregate with 15% reclaimed asphalt pavements (RAP). Hamburg wheel tracking test (HWTT) and semicircular-bending (SCB) test were performed to balance the rutting and cracking performance, while varying the asphalt content (AC) at optimum AC, +0.5% AC, and −0.5% AC. The volumetric and performance test results revealed that the virgin mix met the volumetric specifications but failed to meet the cracking performance requirements. In contrast, the mix with 15% RAP content and a 5.7% AC met the volumetric specifications as well as the rutting and cracking performance criteria. The addition of RAP increased mix stiffness, enhancing rutting resistance, while Optimum +0.5% AC improved cracking performance due to a slight increase in binder content. The results of this study will be helpful in modifying the Superpave mix design to develop a BMD approach for HMA in New Mexico (NM).

Ongoing research at the Illinois Center for Transportation (ICT) is exploring sustainable use of quarry by-products (QB)—residual materials from stone quarrying—as pavement foundation materials. This study investigates how the chemical and mineralogical properties of aggregate QB affect their strength gain during extended cement hydration periods. The QB materials were classified as either dolomite or limestone, based on the Illinois Department of Transportation (IDOT) aggregate chemical testing methods. X-ray diffraction (XRD) analysis was conducted to identify the major and minor mineral phases within these materials. Bender Element (BE) sensors—shear wave transducers—were installed in 3% cement-stabilized QB specimens with varying chemical and mineralogical compositions to continuously monitor strength development during curing at two temperatures, 104°F (40°C) and 70°F (21°C), over a period of 4 months. Limestone QB specimens initially showed higher shear wave velocities (V_s) than the dolomitic QB, indicating a faster rate of hydration under both temperatures. However, over time, dolomitic QB specimens demonstrated faster increases in V_s, suggesting greater hydration and stiffness. This reversal trend indicates that the chemical and mineralogical compositions of dolomitic QB lead to distinct hydration reactions and formation of additional hydrated phases. Further analysis shows that curing lightly cement-stabilized specimens at an elevated temperature of 104°F (40°C) results in an average small-strain shear modulus (G_max) that is 30% higher than that achieved at room temperature.

Expansive subgrades swell and shrink with moisture changes, mainly due to water entering the pavement edges. Large-scale model experiments were performed inside a test chamber measuring 1,500 mm × 1,500 mm × 1,000 mm. This paper proposes a mechanism that simulates the application of differential swell (uplift) pressure applied at the subgrade level through the use of a 250-mm diameter plate. Both unreinforced and reinforced pavement sections, incorporating geogrid and geotextile, were investigated to quantify the reduction in surface heave profile and stress distribution within the pavement layers. The effectiveness of small aperture size (24 mm × 24 mm) biaxial polyester geogrid (GG) of ultimate tensile strength of 100 kN/m and woven polyester geotextile (GT1) of ultimate tensile strength of 100 kN/m was investigated. Model pavements were built with a prepared subgrade thickness of 500 mm, a base course thickness of 250 mm, and a subbase course thickness of 150 mm. Moderate to high swell pressures of 425 kPa were applied at the subgrade level. The study’s findings reveal that the use of reinforcement materials significantly improves surface heave. Among the reinforcements tested, geotextile was found to be most effective, reducing heave by approximately 38% compared to an unreinforced section. Additionally, the reinforcements were found to significantly reduce stresses within the pavement layers, further highlighting the effectiveness of geosynthetics in mitigating differential heave-induced damage.

Highway pavement consists of various layers that are capable of transmitting load from the moving vehicles to the subgrade. Among these layers, base and subbase act as an intermediate medium for transmitting the load from the surface course to the subgrade. A series of repeated cyclic load triaxial tests were conducted on a well-graded aggregate typically used in Illinois. The tests are used to determine cyclic deformation and resiliency characteristics of the aggregate under higher stress ratio (SR) 7, with dust ratio (DR) 0.4 and 0.6, and Plasticity Index (PI) 5% and 9%. The deformation and the resiliency of the specimen are based on dynamic loadings: Haversine and Sinusoidal. The impact of DR was studied for the samples with varying PI and loading conditions and found that the geotechnical precision is required during the construction of the unbound granular materials (UGM). For instance, under sinusoidal loading conditions, the permanent deformation (PD) for low plasticity aggregates with DR 0.4 exceeds the sample with DR 0.6 significantly by 200%−215%. Moreover, with an increase of PI from 5% to 9%, the interaction becomes complex. Therefore, the study investigates the effect of geotechnical parameters and assesses the criteria for determining quality aggregates used in base and sub-base layers of the flexible pavement system.

The higher carbon emissions footprint of widely used cement admixture (0.8 tons per ton) for soil stabilization has driven engineers to adopt industrial by-products or waste-derived materials to ensure sustainability. Ground Granulated Blast Slag (GGBS) is a by-product obtained from the iron manufacturing process and contributes to lower carbon emissions of 0.07 tons per ton. However, the brittleness introduced by higher dosages of GGBS in soil necessitated the inclusion of fibrous content. The present study investigated the influence of GGBS (3%, 6%, 9%, and 12%) and Bagasse Fiber (BF) at dosages of 5%, 10%, and 15% on the Unconfined Compressive Strength (UCS) and durability under alternate wetting and drying cycles of clayey soil. Different curing periods of 7, 14, 21, and 28 days were considered for the modified soil before subjecting to the tests. When GGBS and BF were added separately to the clayey soil, the UCS increased linearly with dosage and curing period up to 12% GGBS and 10% BF. However, the inclusion of 12% GGBS imparted brittleness to the modified soil and caused a marginal increase in failure strain. The combined influence of GGBS and BF in soil increased the UCS by more than 400% at a curing period of 7 days and further improved with a rise in the curing period. Samples admixed with a combination of 9% GGBS and 10% BF sustained up to 12 wetting–drying cycles with mass loss lesser than 15% at the highest curing period of 28 days. The introduction of fibers has reduced the dosage requirement of GGBS and has enhanced the tensile properties of the modified clayey soil. The research findings from the current study indicated that the optimum dosage of 9% GGBS and 10% BF can be utilized to increase the longevity of the subgrade.

The objective of this research was to assess the potential of cellulose nanocrystals (CNCs) at laboratory scale within paving materials that make use of bituminous binders. Brittleness potential as measured by AASHTO T401 protocols was the primary evaluation mechanism where unconditioned, laboratory-conditioned, and field-aged materials were assessed. The investigation was divided into two components, neither of which are prevalent in literature or practice. The first evaluated CNCs within traditional dense graded asphalt mixed at temperatures on the order of 160°C and the second evaluated emulsion-stabilized sand at mixing temperatures on the order of 65°C. The emulsion-stabilized sand was the main focus as it was used to evaluate CNCs’ potential in pavement base layers. The primary conclusion was that emulsion-stabilized sand observed drastic behavior improvements at some dosages across a variety of treatments ranging from unaged, to combined effects laboratory conditioning, to field aging.

Unpaved roads constitute nearly 35% of the roadways in the United States. In Iowa, specifically, approximately 74% of the roadways are unpaved. As the surface layer is the main load-carrying component in these types of infrastructure, the coarse aggregate materials used for its construction regularly break down, resulting in high sand and fines contents. Consequently, the road surfacing materials become more susceptible to the effects of freeze-thaw leading to a decrease in strength and stiffness and resulting in material degradation and surface damage. Previous studies have been conducted on improving the performance of unpaved roads. However, in such studies, CBR tests were typically used instead of resilient modulus, which is a crucial test to evaluate the performance of unbound granular material. In this research, the effect of freeze-thaw (FT) cycles on the stiffness of silty sand geomaterials was evaluated based on their density. Two geomaterials were collected, one from a quarry and one from an unpaved roadway. These materials were tested for their index properties and resilient modulus and were subjected to two and five FT cycles. The results show that the denser material exhibited a higher M_R initially. However, when exposed to FT cycles, the stiffness of the denser material decreased more significantly than that of the less dense material. Additionally, two FT cycles had a greater effect on the stiffness of both materials compared to five FT cycles, which did not present any significant additional effects.

The falling weight deflectometer (FWD) test is routinely used to determine the structural capacity and estimate the remaining service life of airfield pavements. A number of asphalt pavements have not been built to meet minimum design criteria resulting in substandard pavements. This paper presents an alternative approach for the analysis of FWD data to improve the structural evaluation technique for substandard asphalt pavements. The validity of the proposed method was confirmed with data collected during full-scale evaluations of three asphalt pavement sections. Deflection basin parameters were first used to investigate the structural condition of upper, middle, and lower pavement layers at the time of construction. The resolution of the deflection basin was enhanced by constructing synthetic data points. Results revealed the proposed synthetic point method in conjunction with using a non-uniform contact pressure for the FWD plate significantly improved the backcalculated asphalt and base moduli for thin asphalt pavement structures.

The structural integrity of underground structures, such as repositories, pipelines, and tunnels, depends mostly on adequate cementing work. It is pivotal for preventing leaks and soil erosion, securing zonal isolation, safeguarding freshwater aquifers to surrounding structures, and offering longevity. The impermeable nature of cement acts as a barrier, protecting groundwater from contamination and enhancing the durability of underground facilities. Having a low-carbon potential, Type IL cement offers competitive quality and adequate durability compared to Type I cement. This work investigated the flowability, viscosity, and uniaxial compressive strength (UCS) of four cement-based systems (Type I, Type I-bentonite, Type IL, and Type IL-bentonite) to assess their performance in maintaining the integrity of underground infrastructure. The maximum flowability was achieved for the Type IL-bentonite system and it was 9.3% higher compared to the Type I-bentonite system. With a 49.5% reduced viscosity and optimum UCS, the Type IL-bentonite system stands out as a promising option for cementing underground structures.

In model experiments for tunnels, in order to observe the movement patterns of the ground, semi-tunnel models are often employed. An observation plane is constructed using transparent materials and positioned along the symmetrical axis of the tunnel. This arrangement generates friction between the transparent surface of the test box material and the soil used in the experiment, which can affect the measured results. To assess the influences, a proposed experimental method, utilizing laser cameras for both semi-tunnel and full tunnel cases, has been conducted for tunnel models with a diameter (D) of 5 cm. The models incorporate three different types of sand, varying the factor of covering thickness over diameter (c/D) ranging from 1 to 3 for full tunnel cases and from 1 to 5 for semi-tunnel cases. A chart illustrating the variation of surface settlement error in the case of a semi-tunnel, based on covering thickness, was created for three types of sand with varying friction angles. Additionally, another finding showed that the development of the surface settlement area in the direction perpendicular to the tunnel axis was not affected by box wall friction.