Geo-Congress 2024: Geotechnical Systems

On September 28, 2022, Hurricane Ian made landfall near the city of Fort Myers, Florida, as a category 4 hurricane, which brought sustained winds of 150 mph, observed storm surge heights of up to 12 ft, and rainfall totals up to 20 in. Coastal communities around Fort Myers were the most heavily impacted, including 148 deaths and an estimated 113 billion dollars’ worth of damage. The inflation-adjusted economic impact is projected to make Hurricane Ian the third most costly hurricane in United States history. Three weeks after the storm impact, from October 18 to 22, a five-member NSF-sponsored Geotechnical Extreme Events Reconnaissance (GEER) Association team was deployed to Fort Myers and the surrounding areas to study the geotechnical impacts resulting from Hurricane Ian. Primary technologies used to study impacts included a terrestrial light detection and ranging (LiDAR) system, unmanned aerial systems (UAS), soil sampling equipment, and mobile phone cameras. Additionally, two team members returned during November 29–30 to study the recovery progress and implement a multispectral imaging workflow to further investigate impacted structures. Primary surveyed locations include the city of Fort Myers, Fort Myers Beach, Pine Island, Port Charlotte, and the Peace and Caloosahatchee Rivers. Primary observations include a rail bridge failure, sea wall failures, varying degrees of foundation performance, and high degrees of scour and erosion along coastal sites. This GEER deployment allowed for rapid and high-fidelity data collection on impacts related to geotechnical assets following a major hurricane. The dataset and subsequent GEER report from this deployment will allow for improved study of hydraulic and erosional processes related to soil-structure interactions, which will in time improve flood and storm design practices in coastal communities.

In this paper, bioengineering techniques like planting vegetation are presented to address issues related to soil erosion and rainfall-induced hill slope failures. Consolidated drained (CD) direct shear strength tests were performed on soil-root samples with different geometry and root area ratios (RAR) of vetiver roots. Results showed many-fold increases in peak shear strength of the root-soil matrix when compared with control soil samples. The friction angle changed minimally, while the apparent cohesion increased significantly with increasing root density. In addition, two simple mathematical models were developed to predict the increase in shear strength from rooted samples with respect to root area ratio as well as mobilized tensile strength per unit area of soil. In general, the shear strength of rooted soil increased with increasing RAR and mobilized tensile strength of roots. Current studies have endorsed the potential of vetiver grass in stabilizing tropical hill slopes.

Dam embankments are often built with earthen materials as a cost-effective solution to retain vast bodies of water and facilitate the channelization of water flow to meet the supply demands and safeguard the adjacent communities from flooding. The above characteristics deem these assets critical in nature and require frequent monitoring to prevent catastrophic failures. Even though conventional routine inspection practices are widely implemented across the world to monitor and manage these vast assets, they seem to be laborious and time-intensive. Further, only a few data points are captured and interpolated to provide a representative idea of the existing conditions. The in-service embankments undergo change in their surface profile due to the effect of loads, moisture, and weathering. In this study, an uncrewed aerial vehicle (UAV) was used to monitor and build a 3D model of the reservoir embankment. Drone-based photogrammetry has limitations in generating surfaces underneath the water surface. The 3D model from UAV datasets was augmented with extruded planar surfaces to represent a comprehensive model of the reservoir embankment. Two-dimensional (2D) and three-dimensional (3D) analyses were conducted on the embankment slope. Typical practice is to consider a 2D section or, in some cases, an extruded 3D model for conducting slope stability analysis. Interesting observations were made by comparing those results with the safety factor of a whole reservoir embankment model developed with the help of UAV datasets. Overall, the results highlighted the need for using data collection tools like UAVs to obtain a comprehensive 3D model for evaluating the stability of embankment slopes.

Fully grouted vibrating wire piezometer installations provide advantages over conventional open-standpipe piezometers because of faster installation, simpler construction details, ease of multi-sensor installation within a borehole, faster response time, and improved accuracy. However, there remains some lack of confidence in performance when compared to conventional piezometers. For this analysis, fully grouted vibrating wire piezometers were installed at a dredged material management site near the Chesapeake Bay that was subject to tidal fluctuations. The dredged material is underlain by alternating sands and clay. Fourteen new fully grouted vibrating wire piezometers were installed in two boreholes adjacent to a new set of six traditional open standpipe nested piezometers, at depths corresponding to elevations of −4.6 to −38.1 m (−15 to −125 ft). One borehole was filled with a high-permeability grout; the other borehole was filled with a low-permeability grout. Data collection was automated using a data logger and wireless modem. Data analysis focused on comparing fully grouted vibrating wire piezometer results to data from the adjacent standard piezometer. Preliminary findings support the increased usage of fully grouted vibrating wire piezometers.

Static pile loading tests were performed in the 1950s and 1960s to upgrade the Mississippi River and tributaries. The test reports gave rise to several papers in the ASCE Journal and conferences that became important references for the development of state of practice of pile analysis and design. The tests were among the very first to include instrumentation for measuring the strain imposed by the applied test loads. They still contain insights of value to the current practice, and to further that end, some of the results of the tests for the Mississippi River Lock and Dam 4 published in mid-1950s have here been digitized and made available for reanalysis to show, historically, the beginning of understanding how load is transferred from a pile to the soil and, also, to put the papers into the context of aspects in those days not yet recognized, such as residual force and the need for accurate separation of shaft and toe response and analysis applying effective stress conditions.

A finite difference method (FDM) to material point method (MPM) transitioning model is applied to the well-known case study of the Lower San Fernando Dam (LSFD) failure during the 1971 San Fernando earthquake. This model uses an effective stress analysis in FDM during shaking, then a post-shaking total stress analysis in MPM to simulate undrained large-deformation response. Two advances in the Berkeley Geomechanics MPM code used for this case study are a nonconforming traction boundary for hydrostatic pressure and an adhesion boundary for modeling the interaction between the sliding mass and the reservoir bottom. The MPM runout model captures large deformation failure characteristics. Important quantitative metrics include remaining freeboard, crest loss, and upstream runout into the reservoir. Important qualitative aspects include shear banding, blocky features, and toe mass separation and bulging.

Climate change is causing changes in precipitation patterns around the world with some regions experiencing increased rainfall. This increase in rainfall can result in increased instability and landslide risks, especially in those areas with steep slopes and poor soil conditions. For example, the Pacific Northwest has seen an increase in the frequency of landslides in recent years as a result of more intense and frequent rainfall events. In this study, numerical models, developed in SIGMA/W of GeoStudio, were calibrated and validated using the results from a series of experimental models constructed in a Plexiglas container. These experiments were conducted on models with varying slope inclinations, void ratios, and rainfall intensities. The numerical models were then used to study the impact of slope geometry, soil properties, and rainfall characteristics on deformation of real-scale slope failures. In particular, the models were also used to evaluate the seepage velocity of the infiltrating water as well as the deformation affecting the stability of the slope. Seepage velocity was found to increase with an increase in the void ratio and rainfall intensity as well as duration. The time required for the slope to saturate was found to increase with an increase in the void ratio for a constant slope inclination and rainfall intensity. The swell of the slope was found to remain constant with an increase in the rainfall intensity.

Rockfall hazards in the Himalayan Mountain range are a serious concern due to the steep terrain, weak geological structure, and intense seismic activity. Rockfalls are a natural hazard that occurs when large rocks detach from slopes and fall down, potentially causing damage to people and infrastructure. To arrest or deviate the falling rocks, the most effective solution is the construction of rockfall protection embankments (RPE) at the toe of the vulnerable portion of the hill. These embankments are resistant to the heavy impact of rockfall events and have low maintenance and repair costs. This study presents the details of design and analysis of a proposed rockfall protection embankment (RPE) for a rockfall-prone site along National Highway 58, near Saknidhar village of Devprayag District, Uttarakhand, India. A detailed trajectory analysis is conducted for the vulnerable slope to assess the impacting velocity, kinetic energy, and bounce height of the falling rocks. Based on the analysis, countermeasures in terms of RPE and catch ditch are proposed. The RPE is designed based on the peak obtained values from the rockfall trajectory analysis, and its efficiency is assessed using the kinetic-energy criteria based on literature. Furthermore, the dynamic interaction between the falling rock and the embankment is investigated through three-dimensional finite element analysis using PLAXIS 3D software.

Clay embankments used for road, rail, and flood defense infrastructure experience several weather-driven deterioration processes that lead to a progressive degradation in their hydromechanical performance. This paper presents a numerical modeling approach that accounts for the development of desiccation cracking in clay embankments. Specifically, a bimodal soil-water retentivity model was adopted to capture the long-term hydraulic behavior of clay embankments prone to weather-driven desiccation cracking. A numerical model was developed for a heavily instrumented and monitored full-scale research embankment with long-term field data. The model was able to capture the variation of near-surface soil moisture and matric suction over a monitored period of nine years in response to weather cycles. The developed and validated numerical modeling approach enables forecasting of the long-term performance of clay embankments under a range of future climate scenarios.

The typically poor long-term performance of deck expansion joints and the high cost of maintenance of these bridge components have led to an increased utilization of jointless bridge systems such as integral and semi-integral bridges. However, the elimination of expansion joints leads to some adverse secondary effects due to the cyclic interaction of the bridge with the abutments. This soil-structure interaction can cause gradual settlement of the backfill, backfill earth pressure increase, and lateral loading of the foundations. In addition to these issues, it has been observed that integral and semi-integral bridges do not necessarily experience the symmetrical thermal expansion and contraction that is typically assumed in design, even if the structure appears symmetrical in design. As a result, jointless bridges may expand more toward one abutment than the other in response to daily and seasonal changes in temperature. In this paper, some of the potential causes of the asymmetrical expansion of integral and semi-integral bridges are identified and discussed through analysis of some of the past field monitoring data as well as the available data published in literature. The identified causes include minor differences in foundation soil stiffness, depth of the foundation, environmental forces, and more.

Embankment risk assessments informed by two-dimensional slope stability analyses often do not consider three-dimensional effects or address them only qualitatively. However, three-dimensional effects can have a large impact on embankment stability, particularly for dams in narrow valleys, dams where cross sections or material properties change over short distances, and sites where weak layers are present. Factors of safety from 2D analyses are generally conservative and are, therefore, typically considered acceptable for use in evaluating slope stability. However, ignoring 3D effects can result in significant overestimates of risk when assessing potential for slope instability and dam failure. This can lead to overconservative designs, increased costs for rehabilitation, and incorrect prioritization of funding for dam safety programs. To demonstrate the potential influence of 3D effects on predicted dam stability, a case study is presented in which post-seismic stability of an embankment dam was evaluated using both 2D and 3D limit equilibrium as part of a risk assessment. Factors of safety based on 2D analysis were much lower than 1, suggesting post-seismic instability and deformations at the dam could be significant. In contrast, factors of safety from 3D analysis were all near 1 or greater, suggesting post-seismic instability and deformation may be limited. This difference could significantly alter predicted performance of the dam depending on available freeboard, seismic loading, and other factors. This case history demonstrates the importance of considering 3D effects when assessing risks related to dam instability, particularly for dams in narrow valleys where assumptions required for 2D analysis are invalid.

Global stability evaluation is an important component of the overall design of column-supported embankments (CSEs). This paper presents two CSE cross sections that are analyzed using limit equilibrium (LE) procedures that are adapted to account for vertical load transfer to the columns by either modifying unit weights or stresses within the model. The CSE cross sections are also analyzed using the strength reduction factor (SRF) method, and the two methods are compared. The results of the study suggest that the effects of complex shearing that can be modeled by SRF analysis, but not LE analysis, are more significant than the effects of vertical load transfer.

This study addresses the feasibility of using bias reduced SMAP Level 3 enhanced radiometer surface moisture (L3SMP_E) surface moisture estimates to predict and use root zone soil moisture (RZSM) to detect incipient failure conditions at known landslide locations. This was accomplished by: (1) acquiring L3SMP_E data from the NASA SMAP satellite mission over 20 in situ sites in Kentucky, (2) using an ensemble Kalman filter assimilation routine to estimate and reduce biases between L3SMP_E estimates and in situ measurements, (3) using a Kentucky-specific version of the soil moisture analytical relationship (SMAR) infiltration model to estimate RZSM at known landslide sites within Kentucky, and (4) using an unsaturated soil infinite slope stability model to analyze and detect incipient failure conditions at the time of reported landslide occurrence. Four known landslides within the Commonwealth of Kentucky were analyzed during this work. It was observed that RZSM estimated using the Kentucky SMAR model performed well when compared to in situ RZSM estimates. Additionally, inclusion of SMAR RZSM estimates at the four landslide sites was seen to yield stability models that were able to detect strength weakening and incipient failure conditions that aligned well with that of reported landslide occurrences and failure modes. The intent of this study is to show that bias-reduced satellite-based moisture estimates can be used to estimate soil moisture at known landslide sites for use in stability models with success in detection of reported incipient failure conditions.

Highway slopes built with expansive soils are often prone to surficial slope failures due to volumetric fluctuations from cyclic ingress and egress of moisture arising from repeated wet-dry weathering cycles. This periodic shrink-swell phenomenon may result in the formation of desiccation cracks, which result in the transition of strength from peak to fully softened and subsequently result in surficial slope failures. Calcium-based stabilizers such as lime are often used to negate the effects of high-plastic clay by enhancing strength and subsequently reducing volumetric strains. However, cyclic wetting and drying can often impact the long-term serviceability of such treated slopes. A research study was conducted to understand the efficacy of different lime dosages against surficial slope failures. Laboratory studies were performed on untreated, 5%, and 8% lime-treated soils at two different curing periods to estimate the changes in peak and fully softened shear strengths. Rainfall-induced slope stability analyses were performed on a hypothetical slope considering the effects of future precipitation in Texas and determining the stability of lime-treated surficial slope. Preliminary studies indicate that lime treatment improves the fully softened strength, and a unique relation exists between the treated soil plasticity and the secant friction angle values. Stability analyses indicated that the lime-treated slopes are less prone to degradation from repeated wet-dry cycles due to the formation of a hydrophobic and resilient soil matrix. Overall, the study provides a comprehensive insight into chemically stabilized surficial slope failures and the effects of environmental changes on the serviceability of this transportation infrastructure.

It is now widely recognized that earthquake damage of an embankment dam is closely related to a dam’s earthquake-induced deformations and that reliable estimates of seismic deformations are essential to evaluating the seismic stability of dams. Numerical analyses of embankment seismic deformations are now routinely applied in the design of new dams and in the evaluation of existing dams, and nonlinear effective stress analyses are gaining wide appreciation within the engineering profession as a useful tool for the seismic stability analysis of embankment dams. This paper provides an overview of the guidelines recently developed by the Earthquakes Committee of the United States Society on Dams (USSD) for the analysis of seismic deformations of embankment dams. The guidelines provide an overview of current approaches for the evaluation of seismic deformations of embankment dams and best practices for the numerical analysis of seismic deformations and the interpretation of analysis results.

Lightweight aggregate has characteristics of light self-weight and high friction angle; therefore, it has great potential to be used as a fill material in load transfer platforms (LTP) over piles to support embankments on soft soils. This study conducted two spring-based trapdoor tests to investigate the load transfer mechanism of the load transfer platform using Kansas River sand and lightweight aggregate materials. The spring-based trapdoor tests consisted of fill placement and surface loading stages to investigate the mobilization and degradation of soil arching above the trapdoor. The surface loading was applied locally using a hydraulic jack on a rigid footing. The vertical pressures on the trapdoor and the stationary supports were measured using earth pressure cells, and the settlements of the trapdoor and footing were measured by displacement transducers. Test results showed the embankment with the lightweight aggregate as the LTP material could reduce the settlement of the subsoil during the placement of the embankment fill and the footing loading. The embankment with the lightweight aggregate as the LTP material showed better performance in hindering the degradation of soil arching and had less footing settlement under the footing loading than that with the Kansas River sand as the LTP material.

This case history details the unique geotechnical solutions utilized to accommodate the foundation challenges associated with the accelerated replacement of the I-295 bridge over Veranda Street in Portland, Maine. The existing three-span structure was replaced with a new shorter single-span bridge over the course of a continuous weekend outage utilizing accelerated bridge construction (ABC) techniques. This strategy required significant substructure and embankment construction beneath the active existing bridge prior to replacement to minimize activities scheduled for the weekend outage. The existing bridge was supported on battered H-pile foundations driven through up to 60 ft (18 m) of soft Presumpscot Formation marine clay. Settlement using normal-weight embankment material was estimated to exceed 6 in. (152 mm) but needed to be mitigated to avoid inducing bending in existing battered piles, which could otherwise result in deflection or damage to the piles supporting the active bridge above. Low-clearance operations and a deep and sloping bedrock bearing layer further complicated construction. A combination of deep foundation and lightweight embankment options was selected to address the project challenges and prepare the site for the ABC weekend closure. The construction phase quality assurance testing program identified the potential for variability in expanded polystyrene backfill (a.k.a. EPS geofoam) and fortified the need for a rigorous construction-phased testing program on all EPS projects beyond vendor quality control testing and third-party verification. This case history shares considerations and measures taken to successfully construct embankments and substructure beneath active bridge spans. Additionally, the case history examines the EPS testing program implemented during construction to address variability in the properties of delivered EPS fill.

An earth fill dam in Canada exhibited significant deformation in the upstream side after 50 years of satisfactory operation. Studies revealed that the loss of soil shear strength was brought by creep movement. However, the studies were unable to simulate the strain softening of the soil coupled with time-dependent creep movement. To address this, the use of time-dependent model for structured soils (TMS) was proposed. It is an incremental plasticity time-dependent constitutive model based on the modified cam clay. It incorporates the principles of critical state soil plasticity, which can systematically emulate the primary, secondary, and tertiary creep phases under increasing stress levels. The research would allow the assessment of the long-term slope stability of water-retaining structures and the development of remedial measures for existing earth fill dams that do not satisfy modern long-term slope stability dam safety requirements.

Foamed bitumen stabilisation is a technology that allows existing granular pavement structures to be strengthened and made moisture resistant, while avoiding the replacement of the existing granular material. It is believed that foamed bitumen stabilisation provides more resilient and sustainable airport pavements, but that has not been quantified. This research objectively compared foamed bitumen stabilisation of an existing pavement to other common airport pavement rehabilitation options, within the context of a case study on the design of a regional Australian airport. The stabilisation of the existing marginal gravel base course with foamed bitumen and a new asphalt surface was the most financially economical solution, the second most resilient solution, and the most environmentally sustainable solution. It was concluded that the foamed bitumen stabilisation and asphalt surface pavement design was the most sustainable and resilient pavement option. It is recommended that in the future, this comparison be extended to include a whole of life assessment of the different pavement design options.

Laboratory determination of resilient modulus (M_R) is time consuming and requires expensive equipment and extensive expertise. This has led researchers to develop empirical correlations for M_R based on stress state, index, and engineering properties of the soil. In the current study, subgrade soils were collected from 10 road construction projects covering a range of soils (A-1 to A-7-6; untreated to chemically treated) found across Indiana. These soils were tested in the laboratory, and attempts were made to establish correlations between select soil properties such as Atterberg limits, percentage of fines, compaction parameters, and M_R. A review of existing models as well as model verification was conducted for Indiana soils. For untreated specimens, the results showed a weak dependence on deviatoric stress and confining stress, while for treated specimens, it was observed that the model parameters increased with treatment, consistent with an increase in M_R. It was also found that machine learning tools, specifically the gradient boost regressor model, provide better predictions than traditional regression analyses.

To properly model the subgrade soil responses under dynamic loads, permanent deformation and damping characteristics must be studied in addition to the subgrade resilient modulus. Soils having relatively high resilient modulus may or may not have small permanent strains (ε_p) and low damping characteristics (ξ). Therefore, in addition to the resilient modulus (M_R), permanent deformation and damping characteristics also need to be studied for undisturbed subgrade soils to replicate field conditions under cyclic loading properly. This study correlates permanent strain and damping information with resilient modulus testing for undisturbed subgrade soils. For this study, 76 Shelby tube samples of subgrade soils were collected from existing pavements in three different regions: SC-93 in Pickens County (Upstate Area), US-521 in Georgetown County (Coastal Plain), and US-321 in Orangeburg County (Coastal Plain, near the fall line). Statistical models were developed to correlate resilient modulus (k₁, k₂, k₃), permanent strain (α₁, α₂, α₃, α₄), and damping model parameters (β₁, β₂, β₃) with soil index properties for undisturbed soils. Models were also developed to correlate ε_p and ξ with subgrade soils M_R.

The most used rigid pavement throughout the United States is jointed plain concrete pavement (JPCP), providing a service life of 30 years or more. JPCP is proven to be a cost-effective pavement system, providing long service life and other sustainability benefits. The structure of JPCP systems and other critical factors, such as material properties, traffic, and climate, impact the performance and serviceability of the JPCP. The analysis of impacts of all these design variables is necessary to understand the most critical factors affecting JPCP lifetime performance. The state-of-the-art pavement ME design (PMED) software evaluates the pavements’ performance through the international roughness index (IRI), joint faulting, and transverse cracking. This study focuses on performing a sensitivity analysis of the design inputs used in PMED software on the predicted performance of JPCP systems. Simulations were performed using the PMED software version 2.6.2.1 for various JPCP design inputs that include pavement structure, mechanical and thermal properties of paving concrete, climate, and traffic. Variables assessed are coefficient of thermal expansion (CTE), Portland cement concrete (PCC) slab thickness, slab width, slab length, friction loss, PCC shortwave absorptivity, PCC thermal conductivity, dowel diameter, PCC heat capacity, climate, and traffic. The data produced from the PMED software simulations is analyzed based on the JPCP performance indicators. Results on the IRI indicator analysis show CTE, PCC thickness, and climate to have the most impact. CTE, climate, and slab width hold the most impact on the joint faulting indicator. The transverse cracking indicator results present CTE, slab length, and friction loss exhibiting the most impact. It is evident from the sensitivity results that CTE of paving concrete holds the most influence among all three JPCP performance indicators.

In the present study, shakedown approach is used to investigate the effect of stress anisotropy on crushing behavior of granular sub-base. Haversine load was applied on consolidated undrained (CU) granular sub-base specimens (GSB) of 100 mm diameter and 200 mm height prepared at a moisture content of 6%. Cyclic triaxial tests under isotropic compression and consolidation conditions were carried out at three different confining pressures, viz., 50, 100, and 150 kPa. For stress anisotropy, initially the specimens were consolidated isotropically, and to induce stress anisotropy an additional vertical stress was applied on top. Vertical stress to be applied on the top is computed by considering earth pressure coefficient at rest. Both isotropically and anisotropically consolidated specimens were subjected to haversine loading, and the strains were measured. The elastic strain, plastic strain, and plastic strain rates developed in the specimens at the end of 1,000 cycles were compared with respect to shakedown limits prescribed in literature. Plastic strains developed increased at low confining pressures and at high deviator stresses. Analysis revealed that the plastic strains developed in anisotropic consolidation were less than that of isotropic consolidation. It was observed that the additional vertical stress applied on anisotropically consolidated and compressed specimens leads to a denser arrangement of granular materials leading to plastic shakedown.

The primary objective of this study is to analyze the hydraulic characteristics of cement-treated pavement base course, which is fabricated of recycled plastics and recycled crushed concrete aggregates (RCCA). To fulfill this objective, representative cylindrical pavement base course samples, stabilized by certain dosages of cement, have been prepared incorporating both shredded plastics and recycled aggregates, and prepared samples were then subject to constant head permeability test following the standard of ASTM D2434. In this study, three different types of plastics, that is, polyethylene terephthalate (PET), high-density polyethylene (HDPE), polypropylene (PP), have been used in three varied proportions (0%, 3%, and 5%), and four different cement dosages (4%, 6%, 8%, and 10%) have been considered for stabilization purposes. This study comes to opine that percentage of both plastic and cement dosage in respective samples significantly influence hydraulic conductivity numbers of pavement base course. In short, this study did reveal that hydraulic conductivity values tend to lessen significantly with increasing cement dosage, and on the contrary, hydraulic conductivity numbers were observed to increase exponentially with the increase of plastic percentages.

Unbound granular materials (UGMs) are extensively used in pavements mostly as subgrade and subbase materials. Excessive permanent settlement or rutting is the main damage mechanism encountered in UGMs. Rutting is a result of accumulated gradual plastic strain in the subbase and subgrade layers subjected to repetitive traffic loadings. Axisymmetric triaxial apparatus or repeated lateral triaxial (RLT) devices are commonly used to explore the rutting of UGMs. However, these devices are not able to capture the actual stress state generated in traffic. A soil element in pavement layers is in a three-dimensional (3D) stress state and includes all three components of cyclic principal stresses. A typical pavement also can be considered geometrically as a plane strain structure. Accordingly, aim of this study is to carry out experiments to determine the long-term deformation of a silty sand in plane strain and in a 3D stress state using a multistage true triaxial apparatus (TTA). It is found that the permanent deformation of UGMs under plane strain and 3D anisotropic stress state differs significantly from that under axisymmetric stress. An increase in the intermediate principal stress was observed to decrease the total and permanent deformation. An increase in cyclic stress level was also found to increase the rutting in UGMs. The deformation of soil under the plane strain state was found to be less than that in the axisymmetric stress state but falls into an intermediate range when compared to tests involving 3D cyclic loading.

In the last three decades, railways have gradually increased the weight and speed of trains to improve their capacity, profitability, and efficiency. This approach has provided overall benefits; however, it has also led to increased track and structure maintenance costs. The subgrades of railway tracks now experience higher stress, resulting in significant deformation and, in extreme cases, embankment shear failure. Therefore, ground improvement methods should be introduced to reduce stress and deformation in tracks and ensure that the subgrade can safely withstand the increased axle load. One effective ground improvement method is the use of an asphalt layer, which has been successfully applied in many countries. The thickness of the asphalt layer varies from 10 to 20 cm, depending on the regulations of each country. In this study, the finite element program ABAQUS is utilized to model a three-dimensional railway track and investigate the effectiveness of using an asphalt layer to improve the track modulus. The model is calibrated based on experimental observations and used to determine the effects of different combinations of asphalt and granular layers on the stress and displacement of the subgrade under static load. Considering the importance of track modulus in long-term track behavior, the Winkler theory is employed to estimate the track modulus. The results suggest that increasing the thickness of the asphalt layer from 10 to 18 cm significantly reduces the stress and displacement of the subgrade, resulting in uniform displacement.

Soil water characteristic curve (SWCC) which describes the relationship between water content and matric suction is important to analyzing unsaturated soil behavior. Because of the degree of uncertainty in field conditions due to climatic variability and soil heterogeneities, it becomes necessary to probabilistically characterize the SWCC. A satisfactory probabilistic characterization of field-based SWCCs requires a substantial data pair of water content and suction and their distribution characteristics. In this study, the kernel density estimate (KDE) approach was applied to water content and suction data measured from field-installed co-located sensors of a compacted clay bed to (1) determine the modality of water content and suction distribution and their constitutive relationship at variable weather conditions and (2) demonstrate the importance of probabilistic analysis of SWCC. The Gaussian function was used in the KDE analysis. A moisture sensor and soil water potential sensor were juxtaposed at 0.3 m depth of the 3 m × 3 m compacted clay bed to collect the water content and suction data and determine their distribution under the field condition. The density plots of both water content and suction at 0.3 m depth exhibited multimodal distribution due to the uneven distribution of climatic events. The KDE reasonably identified the air entry value, saturated moisture content, and residual moisture content in the field conditions, which were validated with field-based SWCC plots. The study showed that probabilistic analysis better interprets the realistic scenarios of field unsaturated soil behavior.

Degradation of railroad ballast via ballast fouling is a persistent issue for the track structure. Ballast fouling (i.e., intrusion of materials passing the 3/8 sieve) compromises the integrity of the track system by reducing the shear strength and impeding drainage. This research seeks to understand the unsaturated characteristics of ballast fouling materials, including the electromagnetic properties, to further describe ballast aggregate and fouling particle interactions. There has been limited research in geotechnical engineering with complex electrical resistivity, yet it is used in geophysics to study bulk soil properties, particle to particle properties, biofilm formation, and biogeochemical processes. Although the use of this method has had a resurgence in geophysics, most studies are on fully saturated specimens. The objectives of this study were to establish the experimental methods for unsaturated complex resistivity measurements and to highlight the advantages of this measurement with ballast fouling materials. Measurements were conducted in a non-conducting acrylic box from 0.07 to 20 kHz with Cu-CuSO₄ potential electrodes and three current electrode materials: copper, copper foam, and stainless steel. Results indicate that copper foam electrodes were the most optimal for unsaturated complex resistivity measurements. Also, ballast fouling materials were differentiable when fully saturated using complex resistivity, and a different response for each material can be measured at lower levels of saturation. All results were validated using the generalized Cole-Cole model and mean time constants. These findings are significant because the influence of saturation can make discerning different geomaterials in single frequency electrical resistivity measurements impossible. Thus, complex electrical resistivity measurements provide more information about geomaterials than traditional single frequency electrical resistivity measurements. The long-term goal of this research is to establish the unsaturated electromagnetic, suction, and strength characteristics of fouled ballast as a function of the fouling material and moisture content. This will improve our fundamental understanding of ballast degradation characteristics and non-destructive identification of fouled ballast in the field, and ultimately improve the performance and safety of the track structure.

The traditional measurement technique for finding elongated aggregates involves sieve analysis followed by passing each particle through an elongation gauge. In this study, machine learning has been used as a computer vision-based methodology to determine the elongation index of coarse aggregate particles. Images of aggregates were captured, and an algorithm was developed for contour detection of each particle. The particle size and the number of elongated particles were then computed in an automated form. The laboratory test results were compared with the results obtained from a machine learning-based algorithm. The results so obtained on the segregation of particles in various sizes give significant accuracy with a deviation of ±1 number of particles. The method so developed can be used by researchers and field engineers for the determination of the physical parameters of aggregates.

Nowadays, automated plate load tests (APLTs) are used to evaluate the performance in terms of deflection data obtained from different magnitudes of loading. Several back-calculation methods are currently available to determine the pavement layer modulus based on the deflection bowl data obtained from the regular falling weight deflectometer (FWD). However, the configuration and number of sensors used for the APLT slightly differ from the routine FWD test. To determine the pavement layer properties from the APLT, there is a need to develop a back-calculation approach. In this study, a series of pavement analyses have been performed to simulate the loading condition of APLT with a multi-layered elastic analyses approach. The elastic deformations obtained from the pavement analyses were correlated with the pavement layer thickness and moduli based on the artificial neural network (ANN) approach. The feedforward approach of ANN was selected for this study. The developed ANN model was further used to predict the base layer modulus of different pavement sections.

This paper discusses the preliminary findings from a full-scale evaluation of full depth reclamation (FDR) technique and reports the contribution of FDR layers to the overall pavement structural capacity under aircraft loading conditions. A full-scale pavement section, previously trafficked with a heavy tactical aircraft, was selected as a candidate pavement to evaluate the effectiveness of the FDR technique. The existing asphalt pavement exhibited significant structural deterioration with rut depths greater than 59 mm. Nondestructive and semi-intrusive tests were performed to assess the pavement structural condition. The Pavement-Transportation Computer Assisted Structural Engineering (PCASE) software was used to investigate the contribution of the FDR base layers to the overall pavement performance. From this study, the FDR technique improved the structural capacity of a structurally failed asphalt pavement based on falling weight deflectometer data and showed promise as a deployable rehabilitation approach for airfield pavements encountered during contingency aircraft operations in remote locations.

The swelling of expansive soils in the active zone can impose intolerable uplift forces on piles’ skin. Therefore, it is critical to accurately estimate the wetting-induced swelling and drying-induced shrinkage of expansive soils and soil-pile interactions to help minimize damage to the buildings. In this study, a coupled thermo-hydro-mechanical (THM) model is utilized to estimate the active zone, swelling deformation of the soil, and the soil-pile interactions, when the soil is subjected to real-time meteorological data. The THM model and the input thermal, hydraulic, and mechanical data are implemented in COMSOL Multiphysics. The comparison of the simulated swelling/shrinkage deformation with the analytical calculation produced by VOLFLO software showed a reasonable outcome of the numerical model. The coupled THM modeling approach presented in this paper employs a few input parameters that can be measured using conventional methods and can be incorporated in the rational design of pile foundations in expansive soils.

The influence of enzyme-induced carbonate precipitation (EICP) treatment on the unsaturated soil properties of a clayey sand was investigated in the laboratory. The carbonate precipitated by EICP treatment is known to change the porosity and permeability of the soil, but few studies have looked at its effect on capillarity and the soil moisture retention characteristics. The unconfined compressive strength and soil water characteristic curve (SWCC) of a local clayey sand were evaluated for two types of the EICP treatment: a conventional EICP treatment and one using xanthan gum (X-EICP). The EICP treatment was 1.5M:1M solution of urea and calcium chloride mixed with 30 ml/L jack bean urease enzyme solution. For X-EICP treatment, xanthan gum at a concentration of 3 g/L mixed with 3 ml vegetable glycerin was added to an equimolar 1M solution of urea and calcium chloride and 30 ml/L jack bean urease solution. Untreated and treated specimens were prepared in 70-mm-diameter 25 mm-high rings. The specimens were prepared by mixing and compaction of the soil with 24 ml of treatment solution for EICP and 25 ml of treatment solution for X-EICP, then sprayed with an additional 2 ml of treatment solution. The specimens treated with EICP showed no statistical change in the unconfined compressive strength when compared to the untreated specimens, but specimens treated with X-EICP showed a strength increase. The treated specimens showed a decrease in the air entry value compared to the untreated specimen, and the residual volumetric water content was reduced, especially for the specimen treated with X-EICP.

Embankments constructed using compacted fill are initially in an unsaturated condition. Deformations of embankments may occur due to softening effects associated with rainfall infiltration. In this study, a hydro-mechanical coupled constitutive model was implemented in the finite difference program FLAC with the two-phase flow option to simulate the hydro-mechanical behavior of unsaturated soil during wetting. The model adopts the Bishop’s effective stress, which considers the combined effects of suction and degree of saturation on the stress-strain behavior and the effect of suction on the stiffness and hardening parameters. The implemented constitutive model was calibrated using experimental data from triaxial tests. Numerical simulations were conducted for a 6-m-high unsaturated embankment with a slope inclination of 1:1.5 subjected to rainfall infiltration. As water infiltrates into the embankment, the differential settlement on the embankment top surface increases, and the lateral displacements of slope surface also increases significantly. Even though failure may not occur after the embankment becomes full saturation, a potential failure surface appears to initiate at a shallow depth of approximately 2 m from the slope surface. The implemented hydro-mechanical coupled model enables the prediction of failure surface forming within the embankment slope that could lead to serviceability issues subjected to rainfall infiltration.

Climate change and subsequent sea level rise is a global challenge that will have adverse effects on coastal infrastructure. As ocean levels rise, soil water content and pore fluid salinity will change, affecting multiple components of total suction (e.g., matric suction and osmotic suction). This in turn has the potential to change the compressibility and shear strength behavior of soils. Within the realm of unsaturated soil behavior, assessing a soil’s volumetric water content accurately is crucial for characterizing the soil’s thermo-hydro-mechanical behavior. Traditionally, a soil’s volumetric water content can be inferred utilizing sensors that measure the dielectric properties of the soil. Previous studies have shown that the volumetric water content measured based on dielectric permittivity can be influenced by changes in temperature. Therefore, in order to accurately assess a soil’s volumetric water content, an experimental study was conducted to develop a soil-specific calibration model that accounts for the effects of temperature, which can be implemented with commercially available soil volumetric water content sensors. To develop the calibration model, several soil samples instrumented with a capacitance sensor were prepared at various levels of bulk density, volumetric water content, and electrical conductivity. These samples were then hermetically sealed and subjected to temperatures changes ranging from 20°C to 50°C in order to assess the sensor’s performance under different temperature conditions. Results from this study indicate that changes in temperature affect the sensor’s ability to accurately measure volumetric water content and dielectric permittivity. A series of calibration models are proposed to account for these temperature effects, in order to enhance the sensor’s performance under changing environmental conditions.

High school science and math classes can often seem irrelevant to the everyday lives of students leading to difficulties in engaging students in these topics. Moreover, limited opportunities for hands-on learning can further perpetuate perceptions of subject matter difficulty and result in limited exposure to available career paths. By incorporating hands-on curriculum modules in geotechnical engineering, it is possible to overcome these issues while providing students with real-world applications making the material more engaging and meaningful. This paper presents two curriculum modules developed as part of the National Science Foundation-funded Research Experiences for Teachers (RET) site at North Dakota State University. These modules—one for a high school science class and one for a high school math class—were developed with the aim of promoting science, technology, engineering, and mathematics education (STEM), while inspiring students to consider careers in geotechnical engineering. The lessons are designed to align with the Next Generation Science Standards and include hands-on activities along with real-world applications to enhance student understanding of the subject matter. The effectiveness of these modules was evaluated through formative and summative assessment and student surveys. The results indicate that the modules can effectively engage students in geotechnical engineering by connecting the math and science concepts from their classes and increase their interest in STEM fields. These curriculum modules are a valuable resource for high school math and science teachers looking to integrate engineering into their classes.

Teaching and learning have been substantially impacted by the COVID-19 global pandemic induced rapid shift to online and hybrid learning environments. Research has shown that this shift impacted student engagement, learning outcomes, teamwork/group dynamics, and the development of “soft” or professional skills. Although students and faculty have returned to in-person classes, teaching and learning has not returned to the pre-pandemic status quo. Thus, this study presents curricular methods developed and evaluated to enhance student engagement and learning. By providing students with more ownership of their learning and re-engaging them in the process, the students will find value in what they are learning and develop professional skills in their in-person interactions. In the new curriculum, students collaboratively developed their own games (board, dice, card, or computer) rooted in fundamental/technical concepts from the classroom. Over the course of the semester, they built a playable prototype of their game. At the end of the semester, the students were asked to provide a brief presentation of their game, relevant components, and relation to the fundamental geotechnical engineering concepts, and give an overview of the game play. Students then engaged in a friendly gaming session, playing all the games developed in the class. The results indicated that this approach intentionally allows students to explore their creativity while growing their technical competency and professional skills. In particular, (1) students took ownership of the learning process that stemmed from creating their own tools to engage others via future game plays; (2) the design and development process improved goal-setting skills among students; and (3) participation in group activities built leadership, teamwork, and communication skills.

Over the years, several methods to estimate volume change due to shrink-swell soils behavior have been proposed. A portion of those studies focused on the suction effect on volume change, using the suction compression index without taking into consideration the effect of the net normal stress. Others, on the other hand, considered both the net normal stress and the suction stress in an uncoupled fashion. This document presents a specialized laboratory research work aimed at estimating the coupling effect of net normal and suction stresses on the volume change of compacted specimens. A high plastic remolded soil with weighted plasticity index of about 50 was tested under drying conditions using a suction-controlled one-dimensional oedometer apparatus. The volumetric response of the tested soil to the simultaneous application of suction and net normal stress was obtained and compared to that using the sum of the uncoupled stress analysis.

The lack of accessible and affordable education is one of the major obstacles inhibiting upward social mobility of students coming from middle to low socioeconomic backgrounds. The availability and adoption of good-quality visually appealing open educational resources (OER) textbooks has the ability to significantly ease the economic burden on student populations. This case study presents a unique approach to the creation of a visually appealing OER soil mechanics laboratory textbook. The approach consisted of pulling together resources commonly available at the New York City College of Technology and the City University of New York. These include undergraduate research programs, collaborations with visual arts departments, surplus department technician funds, and professional collaborations, among others. We presume that similar resources are available to many universities and colleges across the United States. Of particular interest was the collaboration between a faculty member of the Communication Design Department (the second author of this publication), student artists, and the author of the textbook who is a faculty member of the Construction Management and Civil Engineering Technology Department (the first author of this publication and author of the OER manuscript). The partnership resulted in a novel collaboration model, which was named the designer-director-client model, which aims to develop visual content for science, technology, engineering, and math (STEM) publications. The model paired the manuscript author (client) with student artists (designers) to create visually appealing illustrations under the direction of a communication design faculty member (director). During the process, the designers and art director were compelled to learn principles of soil mechanics to be able to produce technically sound illustrations. This process fostered the general education outcomes of the students involved, while exposing them to a situation common in their field where learning and researching a topic outside of their realm is essential to satisfy the needs of a client. This had the added benefit of propagating general knowledge and awareness of soil mechanics topics to a wider audience. Meanwhile, the author of the manuscript (client) developed a good understanding of the creative process that leads to quality illustrations. The collaboration resulted in a visually appealing, technically sound OER textbook. The model presented in this case study has the potential to serve as a road map for collaborations from other STEM disciplines and beyond.

As a result of the increasingly complex and interconnected problems facing the world, civil (and all) engineers entering the workforce require a more mature sense of engineering judgment at an early stage in their career. The world can no longer afford to wait 15 years for engineers, civil especially, to reach their prime decision-making ability. At the same time, and likely for the same reasons, ABET-aware faculty are grappling with how to develop and assess engineering judgment at the undergraduate level. The goal of our project is to develop and implement various learning strategies and instructional tools to improve student outcomes related to engineering judgment. To begin to address this, a second-year cohort of civil engineering students at Rensselaer Polytechnic Institute, a medium-sized R1 institution which has been producing prominent engineers such as Ralph Peck since the early 19th century, participated in several activities in a required geotechnical engineering course aimed at assessing student understanding of engineering judgment. Open coding qualitative analysis was performed on gathered student definitions of engineering judgment to identify themes within student responses prior to undergoing a design project. Subsequent student submissions to the design project were qualitatively analyzed for employment of these themes within their prepared solutions. Findings suggest that while students included certain subskills in their definitions of engineering judgment, they struggled to demonstrate them within their design submissions. Additionally, analysis of reflection prompts after completion of the design project indicated that students prefer application-based problems to traditional theoretical problem solving. This creates tension with another emerging theme from the reflection prompts: students wished they had more guidance for the open-ended design project. The general nature of application-based design problems, and ultimately experiential learning, is that the learner has limited guidance to fully allow for the individual exploration of the solution space. This work-in-progress paper briefly addresses this tension in student responses, while focusing on the evolution of engineering judgment development in second-year civil engineering students over the course of eight weeks during a required introductory civil engineering course.

The Engineering Buddies program introduces engineering content to middle school students and exposes them to various STEM careers. The faculty, undergraduate, and graduate mentors expose middle schoolers with malleable minds to role models that are relatable and spark curiosity. Faculty and student mentors from four universities visited 19 classrooms across two New Mexico school districts to share their educational path and geotechnical research and create connections with over 700 sixth-grade students in a four-year period. This paper describes and makes available the curriculum, materials, and implementation of an Out-of-School Time program that partners with faculty and students from several universities who serve as role models while introducing middle school students to geotechnical engineering content. The instructional materials, mentoring structure, strategies used, and lessons learned are described.