Geo-Congress 2022: Site and Soil Characterization, Computational Geotechnics, Risk, and Lessons Learned

Evapotranspiration (ET) landfill cover, having several advantages over the conventional cover, is now being widely used for landfill closure. Effectiveness of an ET cover depends on site-specific factors such as climate, soil hydraulic properties, and vegetation. The variation of the degree of saturation (S) and matric suction (Ψ) of soil due to the fluctuation in the environmental parameters, mostly precipitation and temperature may affect the performance of an ET cover. The objective of the current research is to inspect the S and Ψ variation of a test section ET cover soil under actual climatic condition and simulate these results through numerical modeling. Test section ET cover (lysimeter), having dimension of 12 m × 12 m × 1.2 m (40 ft × 40 ft × 4 ft), constructed at the City of Denton landfill, Texas, was selected for this study. Moisture content and matric suction were measured by sensors, installed in the lysimeter at different depths. Local fine-grained soil was used during the construction of the lysimeter. Soil water characteristic curve (SWCC) of the lysimeter soil was determined in the laboratory. Finite-Element (FE) model PLAXIS 2D was used to numerically simulate the water movement through unsaturated soil cover. Based on the input soil and climatic parameters, the change in the Ψ and S was investigated in the model and compared with the field instrumentation data. The generated model could reproduce the relative fluctuation of Ψ and S with the varying precipitation input. The average variation in Ψ and S was found to be 24% and 6.71%, respectively, in the shallower depth (0.3 m), while the variation was found 28% and 22% for the deeper depth (0.76 m). The study revealed that FE modeling can provide a practical indication of soil hydraulic behavior of ET cover systems on a broader scale.

The shear strength behavior of alluvial sand along the Angat Riverbanks in the Philippines was investigated to determine its applicability as embankment material. From direct shear tests, the dry alluvial soil for three initial relative densities and under three normal effective stresses exhibited peak shear strength and dilatant behavior, indicating a brittle failure. The alluvial soil in dry and saturated conditions manifested a strong shearing resistance of 37.52° and 36.61° angles of internal friction, respectively. A constitutive model based on the combined hyperbolic and Weibull functions was formulated. The results of independent actual values versus predicted values provide a good approximation of the constitutive responses of the alluvial soil, both for dilative and contractive behaviors. The simplicity of the direct shear tests and the efficiency of the constitutive model developed in this study are useful for embankment applications of the alluvial soil and the other similar soil types.

This paper describes how an established sand plasticity model was modified to enable the simulation of experimentally observed behaviors of bio-cemented sands under cyclic loading. The proposed model inherits its formulation from PM4Sand, a stress ratio-controlled, critical state-compatible, bounding surface plasticity model, and extends it to incorporate the effects of bio-cementation on the cyclic response of sands. The presented version is preceded by constitutive modifications to better approximate the shear stiffness and strength of a bio-cemented sand. The constitutive equations with major influence on the response of bio-cemented sands are discussed and examples illustrating the modifications to the model are presented together with an initial validation against available experimental data.

In the present study, slope stability analyses have been carried out for the tallest reinforced soil slope failure that occurred at the southwest end of Yeager Airport located in Charleston, West Virginia. Slope stability analyses are performed using limit equilibrium and two-dimensional finite-element method. Limit equilibrium analyses on as built reinforced slope show a line of thrust extending outside the sliding mass. Extension of the line of thrust outside the sliding mass indicates that the soil mass is in tension or numerical solution is unstable. Finite-element analyses indicate yielding of geogrid reinforcement at the design factor of safety. The failure analyses of the slope were explained utilizing formation of a weak plane at the interface of the reinforced fill and shale bedrock. The properties of weak plane were defined using the Generalized Hoek-Brown material model considering softening of shale bedrock. The results revealed similar progressive failure of reinforced soil slope as observed in the field.

During the liquid limit (LL) testing on diatomaceous soil from the fall cone and Casagrande cup tests, some eccentric behaviors have been observed: (1) There are inconsistent LL results of diatomaceous soil using the fall cone (BS 1377) and Casagrande cup (ASTM D4318) method. Based on the current criteria of these standards, the LL for diatomaceous soil tested with the fall cone is much higher (approximately 30%) than that from the Casagrande cup. (2) With the Casagrande cup test, diatomaceous soil slides towards the groove instead of flowing plastically as is assumed in the slope stability framework used for data interpretation. This may be related to the underpredicted LL from the Casagrande cup test. (3) Both tests expect the specimen to be tested from dry state to wet state, which leads to little water content change during the whole test for diatomaceous soil. Hence, there is a distinct difference between running the tests from dry to wet and wet to dry for diatomaceous soil, resulting in different LL and flow indices. In the current work, we perform laboratory vane shear tests to accompany fall cone tests and Casagrande cup tests and adopt the well-accepted theory that the undrained shear strength of fully remolded fine-grained soils at their LL is around 2 kPa (typically 1.7–2.3 kPa). We also consider modifications to the test procedures and equipment: coat the Casagrande cup with sand to force the flow failure mechanism and run both tests from wet state to dry state. Preliminary results from testing are presented and discussed.

Hvorslev’s theory states that the true friction angle and the base friction angle (or Hvorslev’s constant) are fundamental properties of soils that remain constant regardless of the overconsolidation ratio. The use of the true and base friction angles allows for the determination of the traditional shear strength parameters without the need to conduct testing for different stress histories. Despite the importance of these parameters, there is little study available on understanding these parameters for different types of soils. In this study, laboratory prepared mixtures of montmorillonite, kaolinite, and quartz were overconsolidated in an oedometer before their strengths were measured in a constant volume direct simple shear device. The samples were tested at overconsolidation ratios ranging from 1 (normally consolidated) to 32. The results obtained were used to determine the values of the true and base friction angles. Values of the base friction angle were found to depend on the dominating clay mineral. In montmorillonite-dominated soils, the base friction angle remained nearly constant regardless of the plasticity index. However, it was found to increase with an increase in the plasticity index in kaolinite-dominated soils. For both montmorillonite- and kaolinite-dominated soils, the true friction angle would decrease with an increase in the plasticity index for soils with plasticity indices less than 80. An increase in the plasticity index beyond 80 did not result in significant changes in the true friction angle.

Three conical load test-induced settlement tests were conducted to find the most suitable stiffness correlations using the results of standard penetration and piezocone tests in Central Florida soils. The soil conditions at the test locations were studied using different field tests, which were utilized to define a summarized soil profile and to determine instrumentation location and soil sampling procedures. The three conical load tests were instrumented with piezometers, inclinometers, magnetic extensometers, pressure cells, settlement plates, and a vibrating wire settlement transducer. Soil samples were retrieved from boreholes nearby the conical load test locations. The results of the conical load testing field measurements were employed to validate influence zones, incremental stress variations, and soil stiffness mobilized by the conical load test arrangement. The experimental procedures and test results were simulated in PLAXIS 2D and the small-strain constitutive soil response of underlying soils was benchmarked in light of the field-testing results. The authors found reasonable match between measured and computed results when the small-strain stiffness is properly accounted for in the numerical simulations.

This paper discusses the use of Crayola modeling clay as a substitute for natural soil. This product is relatively inexpensive, non-drying, reusable, pliable, and commercially available. The unconfined compression test was performed to determine mechanical properties. Additionally, inverse analysis was implemented to characterize the elastoplastic response. The model used in the inverse analysis considers finite deformation plasticity. The stress–strain relationship was obtained by defining a local dissipation function and using the principle of maximum dissipation. The formulation is based on hyperelasticity and expressed in terms of Kirchhoff stress, logarithmic strain, and the multiplicative decomposition of deformation gradient to overcome the limitations of the theory based on infinitesimal deformation. The hardening behavior is prescribed based on Ludwik’s equation. Inverse analysis is performed using a genetic algorithm to minimize the difference between the experimental data and predicted results for the unconfined compression tests.

In order to understand the effect of size of landfill on heat accumulation, heat loss, and resulting temperatures, heat generation and heat loss were simulated using the commercial 3D geothermal simulator TETRAD. Three landfills were simulated each having the same total volume of 16.7 × 10⁶ m³, liner areas ranging from 33.5 ha to 55.8 ha, and total heights ranging from 75 m to 121 m. The shape of all simulated landfills was symmetrical pyramidal frustum. Heat generation in all landfills was simulated by assuming an average waste heat generation rate of 0.5 W per cubic meter of waste. The temperatures of the waste simulated by the model for the first 10 years were plotted for comparison. The peak simulated temperature in these landfills was about the same. However, median temperature or average along a vertical axis passing through the center of landfill was slightly higher for the tallest landfill and slightly lower for the shortest landfill compared to the baseline landfill. This numerical study indicates that, flatter side slopes will have greater heat loss and lower median temperature than landfills that have steeper side slopes.

The magnitude of the overall settlement of soil depends on several variables such as the compression index, C_c, and recompression index, C_r, which are determined by a consolidation test; however, the test is time-consuming and labor-intensive. Correlations have been developed to approximate these compressibility indices; however, the level of accuracy significantly varies. Particularly, those correlations were empirically developed with local geotechnical data. In this study, the accuracy of the existing correlation was evaluated using the Florida soil database, and new compressibility prediction models were developed for Florida soils. The statistical models were constructed through a forward-selection stepwise regression procedure. Multiple variables were used, and these variables included natural moisture content, overburden stress, liquid limit, and specific gravity. The best-performing statistical models of soil compressibility were constructed for clay soils.

Ballast fouling reduces the hydraulic conductivity and strength of ballast and can be detrimental to track performance. Therefore, it must be remediated when detected. While saturated and highly fouled conditions are readily detected using nondestructive methods such as ground penetrating radar, low to moderate fouling and unsaturated moisture conditions still pose a challenge. The objective of this research is to study low to moderately fouled ballast as a function of the interrelated properties and the strength and deformation response. The water holding capacity and shear strength were tested on one ballast aggregate and two different gradations of sand fouling materials which were collected from in service track. This paper describes the experimental methodology for ensuring replicate, large samples were tested at the same relative density, volumetric water content, and degree of fouling between two laboratories. The results showed that the strength of the ballast decreases continuously with the increase of the fouling percentage and water content intensifies the strength loss. Furthermore, it was found that the gradation of the fouling material is a critical factor influencing the mechanical response of the ballast. This study can shed light on the relationships between fouling, moisture, and ballast strength and deformation in varying conditions.

Glauconite is an iron potassium mica with a characteristically green color and low strength, often found in peloidal form. Glauconite generally forms under reducing conditions within a shallow marine depositional environment. It has been observed in coastal regions on the East Coast of the USA, including locations along the Atlantic outer continental shelf (OCS) associated with wind farm developments. Due to its friable nature, glauconite can influence the geotechnical properties of the sandy soils in which it is found. Intact glauconitic sand exhibits high strength, but under moderate disturbance is relatively brittle, similar to carbonate sediments. This paper presents a geological review of glauconitic sand formation, describes its depositional environment, presents some of its geotechnical characteristics, and provides insights into the impact of glauconitic sand on offshore foundation installation and performance.

Accurate quantification of the soil-structure interface shear resistance of shallow foundations, pipelines, tunnels, and other intermediate structures under relatively low normal stress can be difficult. Standard geotechnical testing devices are generally designed to handle large stresses associated with deep foundations and large, heavy structures. At low normal stress, measured interface shear resistance can be complicated by artificial friction from the equipment itself. Over the past decade, various commercial geotechnical laboratories and research institutions have independently developed bespoke solutions to avoid these complications, including tilt tables, modified direct shear boxes, modified ring shear devices, and 1g model test devices. This paper presents a large database (>400 tests) of interface shear test results on a wide range of natural sands and clays performed under low normal stresses. The data populate a conceptual framework that illustrates the factors governing interface shear resistance, comprising soil minerology, soil drainage, normal stress, overloading history, and interface roughness.

Data of over 30 (1D) consolidation tests on slurry type soils used in marsh land creation projects along Louisiana coastline were analyzed and assessed, and regression equations for Louisiana mash soil were proposed to estimate the compression index. It had been discovered that the compression index predicted by a simple linear equation considering natural moisture content, initial void ratio, plastic limit, and liquid limit, etc., could moderately assess the genuine soil compression index. During this study, sedimentation state of natural clay (Δe_r) is defined as the difference in the void ratio between natural clay and remolded clay at the pre-consolidation pressure. The sedimentation state of Louisiana marsh soils was quantified, and consequently, the empirical equations considering the sedimentation state were developed. It is noted that, for Louisiana marsh soil, the equations considering the sedimentation state provide a significantly better accuracy than the equations with multiple soil properties, which might be more useful to gauge soils’ compression index having a wide effective stress range in its consolidation process. Utilization of the empirical equations recommended might lead to a valuable tool to assess the compression index of the marine clayey soils in the wetland recovery projects in coastal Louisiana.

Triaxial tests have been extensively used in geotechnical engineering to determine soil characteristics and investigate soil behavior. However, little research has been carried to evaluate important aspects of common triaxial testing that can cause misleading interpretation of soil properties. The key reason for this is the absence of a proper and affordable method to monitor the actual soil behavior during various steps of triaxial testing. Recently, a photogrammetry-based method was proposed and proved highly accurate measurements of local, total, and absolute volumes, specimen deformations, and strain localization. This paper suggests a practical re-evaluation of some aspects and practices in the conventional triaxial testing by applying the advancement of the photogrammetry-based technique. The analysis of a series of drained triaxial compression tests using the photogrammetry-based method proved the ability to determine the tilting, the misalignment, and the likelihood of leakage during saturation of soil specimen, and the preparatory, consolidation, and shearing stages of triaxial testing. The experimental results presented relevant insights about the major errors during laboratory procedures and testing including the deviation of the effective stress path, maximum shear stress, axial strain, stress–strain relationship, and soil strength. The measurement of the eccentricity and tilting angle of soil specimen provided proof of potential errors and are recommended to be considered to evaluate the reliability of soil characteristics measurement during triaxial testing. In addition to that, the procedure presented in this paper reinforces the importance of the adoption of the photogrammetry-based method to accurately determine the soil properties during triaxial testing.

Atterberg limits are the index properties determined in almost every site investigation when plastic soils are encountered. They are used in soil classification as well as in estimating important soil properties needed in the design and analysis of many common geotechnical engineering problems. Results from the conventional method of quantifying the liquid limit (LL) via Casagrande percussion cup device are influenced by repeatability issues due to various factors like the operator dependency among others. The fall cone device offers many improvements over the Casagrande cup, including simplicity in test performance, easier maintenance, lower sensitivity to equipment manufacturing variations, reduced operator dependency, and it allows LL determination on low-plasticity soils. In this paper, a review of previous studies on the comparative results from the two devices is presented. Based on extensive laboratory testing on soil samples collected from Indiana state, fresh results from the two devices are compared and contrasted with those from previous studies. The findings will incentivize practitioners to employ a simpler device for routine laboratory testing that leads to greater reproducibility and reliability in the fundamental measurements needed for every geotechnical site investigation.

Determining the water content of soil through conventional means of oven-drying is a time intensive process that typically requires a drying period of 24 h. A method to rapidly obtain water content measurements through remote sensing means, without a priori knowledge of the soil properties, was investigated. Reflectance measurements were collected from filter paper that was in direct contact with laboratory prepared clayey and sandy soils. Linear correlations were developed between the reflectance measurements and the associated volumetric water content of each soil sample after the soil samples were in contact with the filter paper for five minutes and two hours. Several data analysis techniques were investigated, including reflectance values at specific wavelengths, established indices, and a continuum analysis across water absorption bands. High correlations were observed for individual soil types. The highest correlation coefficients (R²) obtained for each soil type are as follows: 0.93 for kaolinite (waveband depth at 1,900 nm from the continuum analysis), 0.99 for red dirt (reflectance at 1,900 nm), 0.99 for silica sand (reflectance at 970 nm), and 0.99 for a poorly graded sand (reflectance on continuum line at minimum value near 1,450 nm). The correlations decreased when soil types were combined; the best correlation of 0.87 occurred for the combined clayey soils using the waveband depth continuum analysis at a wavelength of 1,900 nm. Based on these correlations, a linear relationship between water content and reflectance measurements may exist, enabling a rapid (5 min) measurement of soil water content.

Static liquefaction has been associated with numerous recent failures of tailings storage facilities (TSFs) around the world. These failures lead to devastating consequences for the environment and civil infrastructure and lead to the loss of human lives. In this study, we present trends for the response of mine tailings to monotonic loading considering (1) triaxial tests, (2) bender element tests, and (3) consolidation tests performed on mine tailings. These materials have a broad range of states (i.e., from very loose to dense states), a range of particle size distributions (i.e., from silty sand to almost pure silt mine tailings), and a broad range of compressibility. The trends are evaluated in the context of static liquefaction using critical state soil mechanics concepts considering different state definitions. In particular, we present trends for shear strength (residual and peak), state and brittleness soil indexes, and excess pore pressure indexes. Finally, static liquefaction screening indexes are proposed based on the observed trends, highlighting that static liquefaction is just another facet of soil behavior under monotonic loadings, and hence it should be explained under a mechanistic framework.

The compressibility characteristics, effects of low-strain rate, and natural variability in fines content of Central Florida sands are examined in this paper. Soil samples arising from the same sedimentary depositional environment in the Central Florida region were extracted from a site near the University of Central Florida campus. Soil characterization methods included the results of index, X-ray diffraction, and scanning electron microscopy tests. Compressibility characteristics of the soils were studied under constant rate of strain conditions at different densities and low-strain rates on reconstituted sand specimens. The results were evaluated in terms of axial stress–strain response, overall compressibility properties, potential of compressibility, and fines content. This paper shows how a small variation in both vertical and horizontal distance at which the samples were extracted triggered significant differences in the compressibility characteristics of these soils. Negligible low-strain rate effects were observed in the tested specimens.

In this study, the internal structure of the individual particles of carbonate sands of both biogenic and non-biogenic nature is investigated using X-ray Micro-Computed Tomography. Pore networks in the internal structure are extracted and quantitatively analyzed. Our results clearly showed that carbonate sand particles have complex internal structures. The biogenic grains have higher internal porosity with minimum of 25% with regular network of interconnected pores, while for the non-biogenic grain, an irregular structure with isolated pores is identified. The internal porosity is only 4% that compared to biogenic grains is at least 6 times smaller. The results of this study can give insights on the breakage mechanism and crushing strength of the individual particles of carbonate sand and consequently their bulk behavior. Also, these results can be used as inputs in the numerical simulations in grain-scale behavior studies.

Recent studies indicate low to medium plastic soils can fluidize and spread over the track surface, i.e., mud pumping, although, the question on the influence of plastic parameters such as the plasticity index (PI) and fines content on mud pumping has not been well understood. This study therefore aims to investigate the role of plastic parameters on the subgrade instability through a series of field and laboratory studies. The site investigations show that all soils collected from mud pumping sites have PI smaller than 26 while poor drainage condition is found as a major factor causing subgrade fluidization. The laboratory study shows that the specimen experiences a redistribution of water content at an adverse loading which transforms the top portion of the specimen to a fluid-like state. Kaolin content significantly affects the cyclic response of subgrade soil as increasing this fraction to a reasonable degree can mitigate soil fluidization.

A previous study by the authors showed that the rotational movement of a penetrating rod could reduce the penetration resistance. In this study, the effect of rotation on penetration is further studied to shed light on the design of a seed-inspired self-burrowing robot. Three penetration strategies were modeled using the discrete element method: (1) control case, (2) whole-body-rotation (WBR) case, and (3) cone-rotation (CR) case. It was observed that the cone penetration resistance could be reduced to similar levels due to WBR and CR at the same rotational speed. Further analysis of particle–penetrator contact data unveils that rotation of the cone reduces the contact number, and the magnitude of the contact forces. A slight reduction of the shaft friction is also observed in WBR cases, yet with a cost of much higher energy consumption to induce the rotation of the shaft. Comparing the three penetration strategies, the CR strategy is considered the most suitable for a self-burrowing robot as it reduces penetration resistance with the lowest energy consumption.

Many organisms adopt well-evolved strategies and traits to facilitate burrowing/penetration in soils. Example features include the “dual-anchor” strategy used by razor clams and rotational drilling adopted by scarab beetle larva and some seed awns. Overall, underground burrowing requires overcoming resistances to advance forward and forming anchorage to prevent slip backward. Inspired by the aforementioned self-burrowing features, we designed a modular horizontal burrowing robot that features an extensible body and a rotatable tip. The robot was buried 7 cm below the surface of a bed of glass beads, and burrowed by cyclically alternating extension/retraction of the body segment, facilitated by the rotation of the tip. The burrowing performance of the designed robot was evaluated under different tip designs and control strategies. Insights into the general principles of burrowing in granular media were discussed by comparing to swimming in low Reynolds number fluids.

Miniature cone penetration testing (CPT) is now widely used in centrifuge modeling. A common approach for interpreting the test results is to normalize the measured cone tip resistance, q_c, to the value that would be measured in the same soil at an effective vertical stress of 1 atm, q_c1. However, most overburden normalization methods are derived from CPTs performed in calibration chambers or from CPTs performed in the field in relatively uniform deposits. This paper summarizes measurements from in-flight miniature CPTs performed in clean sand centrifuge models where tip resistances were measured continuously to an effective vertical stress larger than 1 atm without any significant boundary effect or particle size effect. Based on these test results, the authors present a centrifuge CPT-specific overburden normalization for a wide range of sand relative densities, ~40%–90%. The in-flight miniature CPT data suggest that the overburden normalization exponent m generally is insensitive to relative density and is somewhat larger than the values computed using methods from the literature.

Spatial variability of geotechnical engineering parameters is an incontrovertible feature, which cannot be overlooked when embarking on stability analyses in soil mechanics. A plethora of methodologies and studies is reported by different researchers across the globe, all bearing witness to the crucial importance of the probabilistic/stochastic variation of soil strength parameters. However, the reliability of different methodologies in substantiation of the inherent variability of natural deposits is not necessarily similar. Chronologically, the Random Finite-Element Method (RFEM) first emerged to contribute to this field. However, with some very promising results, it now transpires that the Random Limit Equilibrium Method (RLEM) is a very robust technique in slope stability analysis, when comparing both the accuracy and time efficiency involved in the calculation process. The current study aims to shed more light on the issue by investigating some comparative stochastic slope stability analyses. Results of some RLEM slope stability analyses are compared with some corresponding RFEM results on a one-on-one basis. The brilliant performance of RLEM in this study obviates the need for cumbersome RFEM calculations, at least in the realm of stochastic slope stability analysis.

Seismic risk assessment of critical infrastructure requires information on the structure and its vulnerability, probability of failure, and hazard. When considering underground infrastructure such as pipelines, the occurrence of liquefaction will directly impact its performance due to the induced permanent deformation. Intensity measures such as peak ground acceleration (PGA) and peak ground velocity (PGV) are already included in several fragility curves for seismic risk assessment. Nevertheless, estimation of this permanent ground deformation (PGD) requires additional data. One of the sources of permanent ground deformation is liquefaction. Liquefaction can cause lateral spreading and post-liquefaction settlement that depend on the shear and volumetric deformation the soil experiences during the cyclic loading. There are several simplified procedures that can be used to assess liquefaction potential and both types of deformation, but they depend on how well-characterized the soils in the area of interest are. Mapping of liquefaction can be based on a critical layer or on a soil profile. Besides, approaches can be deterministic or probabilistic considering uncertainty in the seismic scenarios and soil conditions. This paper is aimed to summarize these procedures, pointing out their strengths and limitations. A methodology is defined for estimation of PGD and mapping that can lead to development of fragility relationships. A case study is presented for the City of Valparaiso, in Chile.

Sanford Dam is the largest of the dams and impounds the signature lake in the City of Boiling Spring Lakes. Following initial impoundment behind Sanford Dam in the early 1960s, local residents observed the first of multiple uncontrolled lake draining events that would occur during the dam’s nearly 60 years of service. During Hurricane Florence in September 2018, Sanford Dam breached due to overtopping. The City elected to reconstruct, which afforded an opportunity to evaluate the dam and its foundation. A review of historical records and the performance of additional subsurface investigations revealed conditions which present a risk to the dam’s safety. This paper will include a review of historical accounts of unexpected losses of the lake, a summary of the local geology and subsurface conditions revealed during subsurface investigations, an explanation of the failure mode considered most critical to the dam, and a description of the measures designed to address the threat posed by the site conditions.

Pile-founded T-walls are widely used for levees in New Orleans and other regions of the United States as a key infrastructure for flooding protection. Traditionally, the safety evaluation of pile-founded T-walls follows a simplified deterministic procedure. It is critical to evaluate the performance of the pile-founded T-wall in a probabilistic manner under the potential flooding hazards. This paper presents a study for the safety assessment of the pile-founded T-wall system in the face of flooding hazards using both deterministic and probabilistic procedures. First, the deterministic analysis for the performance assessment is performed using the three-dimensional finite-difference modeling. Then, uncertainties in geotechnical strength parameters are considered using Monte Carlo simulations and finite-difference modeling to evaluate the variability of the performance of the pile-founded T-wall under different flooding hazard levels in a probabilistic manner. The resulting factor of safety curves of pile-founded T-walls in both deterministic and probabilistic manners under various flooding hazard levels are analyzed. It is observed that the mean factors of safety obtained using Monte Carlo simulations are very consistent with the results from deterministic analyses. However, with the probabilistic analyses, the variability of the factor of safety due to input geotechnical uncertainties can be explicitly evaluated. The safety assessment framework is demonstrated through a case study of the pile-founded T-wall design.

Backward erosion piping (BEP) is a leading cause of failure in dams and levees, but uncertainties in erosion progression characteristics and soil properties provide significant challenges to a deterministic analysis approach. For this reason, a risk-based approach to BEP failure is of great interest to engineers. The probability of failure is most commonly determined through the use of event trees and engineering judgment. When using this approach, geologic variability in the subsurface is incorporated into risk analysis through estimates of subjective probabilities regarding the existence of a continuous, erodible layer in the foundation. Recently, however, there have been developments in the random finite element method (RFEM) modeling of BEP progression that have demonstrated alternate means of assessing the probability of pipe progression in spatially variable soils. In this study, an RFEM model for BEP progression is presented. Results are presented to illustrate the influence of soil variability on the probability of BEP progression. Results indicate that the probability of BEP progression increases as the spatial correlation length increases.

The Georgia Department of Transportation (GDOT) has been managing transportation assets according to Georgia’s Transportation Asset Management Plan (TAMP), which delineates the best practices, strategies, and priorities to enhance assets preservation over time. Bridges and pavements are managed by their respective Divisions, which are responsible for periodically assessing the asset’s condition and establishing the best long-term life-cycle strategies by considering critical assets and limited funding. However, geotechnical assets (e.g., retaining walls, embankments, slopes, or bridge foundations) have rarely been tracked, despite the fact that their failure may lead to significant traveler delay and safety concerns. As part of ongoing efforts, we have documented the historical development of geotechnical asset management (GAM) practices in the United States and put them in the context of practices in Georgia, which are in an early stage. The information discussed in this study will set the stage to develop a GAM program in the state of Georgia.

During a career spanning over 45 years, the author was involved with forensic analysis on over 50 legal/forensic cases involving geotechnical issues. This paper presents summaries of 10 cases involving geotechnical failures, the cause(s) of these failures, and common threads in all these cases regarding lessons that can be learned regarding the reasons for failure. The cases involved retaining walls, slopes, soil compaction, water pressure, and compressible soil. Failures occurred due to poor understanding of the risks involved, a lack of proper geotechnical engineering involvement, poor communication, and a tendency to not spend enough resources to complete a thorough design. These case histories show that to reduce the risk of geotechnical failures, owners/clients should be advised to retain geotechnical engineers with the best local knowledge, experience and expertise; be willing to pay them appropriately for their capabilities; and keep the geotechnical engineers actively involved with both the design and construction teams.

An underground 1.9-mi-long (3.1 km) sanitary sewer line was designed and constructed in the greater Seattle area. Once completed, substantial groundwater seepage was observed within a 600-ft-long (183 m) segment of the pipeline. The repair to arrest the seepage cost over $1 million and resulted in a six-month service delay. Geotechnical studies identified groundwater conditions consisting of shallow and deep aquifers separated by a confining unit. The construction contract specified using a combination of trenchless and open trench construction methods. Anticipating flowing artesian conditions in the seepage area during construction, a dewatering system was installed. The trenchless installation in the seepage area used an H-pile shoring system for the receiving pit. Once the dewatering wells were decommissioned, seepage was observed from the newly decommissioned wells and shoring system. This case study provides relevant lessons learned and recommendations for future project planning, design, and construction.

The Gilder Center for Science, Education and Innovation (SEIC) is the newest expansion of the landmarked American Museum of Natural History (AMNH), and will function as a state-of-the-art scientific and education institution. Bold and modern architecture define the five-story structure, which includes a 6-m deep cellar level. The about 4,500-sq-m footprint of the SEIC is adjacent to seven museum buildings, each built between 40 and 130 years ago. The general subgrade for the SEIC cellar was up to 2-m below the lowest levels of the adjacent buildings, and involved localized excavations for new foundations and mechanical pits extending up to 3-m below the lowest levels. Excavations for footings and pile caps, up to 6-m below the proposed cellar level, were adjacent to active utility lines servicing the museum. Shallow groundwater and layers of thick clay and highly weathered bedrock further complicated the foundation support and temporary excavation support design and construction. The approach to the SEIC expansion of the iconic museum, located in a historic neighborhood with vast differences in subsurface conditions across the project site, could only be achieved with a variety of foundation types and excavation support and underpinning systems, coupled with careful inspection.

The Annex D in the latest edition of the international standard General Principles on Reliability for Structures (ISO2394:2015) recognizes that the geotechnical reliability-based design should place site investigation and the interpretation of site conditions as the cornerstone of the methodology. The geotechnical reliability analysis is sound only when the source uncertainty—the interpretation of site conditions—is well quantified. It is a consensus that probabilistic subsurface stratification is still an open question in geotechnical engineering. The gap lies in the difficulty of developing an uncertainty-aware integration of subjective engineering judgment and the sparse objective site exploration data. In this investigation, a stratigraphic uncertainty quantification approach is developed by integrating the Markov random field (MRF) model and the discriminant adaptive nearest neighbor-based k-harmonic mean distance (DANN-KHMD) classifier into a Bayesian framework. To demonstrate the effectiveness, both synthetic and real-world examples are illustrated.

Structure 67 at Tennessee Valley Authority’s Shelby Dell transmission line sits 175 ft (53 m) above the Mississippi River, adjacent to a bluff that has experienced about 300 ft (91 m) of erosion since the late 1980s. The soil conditions at the bluff include collapsible loess near the top of the profile, and stiff clay that is susceptible to river scour below. The rate of erosion was estimated at 8–20 ft (2.5–6 m) per year. The project team designed a steel sheet pile wall with tiebacks to protect the tower. The sheet pile wall was designed to resist up to 20 ft (6 m) of erosion down its face, adding an estimated year or more of protection from bluff erosion for the tower. This paper provides an overview of the erosion evaluation, alternative repairs considered, sheet pile wall design and construction, and monitoring of the bluff during construction.

The Millennium Tower is a 58-story reinforced concrete building constructed in San Francisco, California, between 2005 and 2009. The Tower is founded on an embedded pile-supported mat with pile tips bearing in dense marine deposits that overlie an over-consolidated marine clay layer (Old Bay Clay). This clay layer experienced stress increases from Tower weight and from multiple episodes of dewatering in the vicinity of the Tower between 2006 and 2018. Settlements of the Tower foundation have been measured since 2006 and lateral deflections of the Tower have been inferred and measured since 2009. The degree which observed settlements can be captured with one-dimensional methods of settlement analysis were investigated. The analyses show that settlements were caused to a large extent by consolidation associated with tower weight and temporary stress increases from dewatering, along with secondary compression. A companion paper presents the three-dimensional analyses of foundation movements.

Seasonal variations and climatic events cause fluctuations of water content and temperature in shallow unsaturated soils. Such fluctuations can alter the resilient modulus (M_R) of subgrade, which is an important parameter in the design and evaluation of pavements. This paper presents a new model to determine M_R of unsaturated subgrade soils under concurrent changes in water content and temperature. The proposed analytical model offers the following two new features distinguishing it from alternative models: (1) the model separately accounts for two different soil water retention mechanisms, namely capillary and adsorption, which enables it to predict M_R over a wide range of suctions, and (2) it explicitly incorporates the effect of temperature in the calculation of M_R through employing temperature-dependent expressions for matric suction and the soil water retention curve (SWRC). The proposed model showed high accuracy when validated against experimentally measured M_R values for several different soils reported in the literature. The presented model is simple and can readily be employed in practice to determine M_R of subgrade soils under concurrent variations of water content and temperature.

Breach due to overtopping is the most prevalent failure mode of levees; therefore, special consideration should be given to this mechanism when conducting levee risk assessments. The main objective of this study is to apply a recently developed logistic regression model, which estimates the probability of breach due to overtopping, to levee risk assessment. The model is first introduced, and then employed for risk assessment purposes by comparing probabilistic model estimates to the results of eight semi-quantitative risk assessments based on expert elicitation of subjective probability. The model is then validated by testing model accuracy using data from 11 new levee overtopping events. Findings suggest that the proposed logit model can support risk assessment by offering a viable alternative for estimating the system response probability of levees when overtopped.

The breaching of the Edenville Dam and overtopping of the Sanford Dam on May 19, 2020, have been the focus of significant geotechnical investigation, while considerably less scientific focus has been directed towards documenting the resulting damage to highway embankments, bridges, and homes downstream of the dams. The Geotechnical Extreme Events Reconnaissance Association deployed a small team to conduct field reconnaissance after the event with the goal of making preliminary observations of impacts to geostructures downstream of the Edenville and Sanford Dams. Damage was concentrated in the city of Sanford while in the city of Midland, downstream of Sanford, flood waters did not reach heights that caused significant damage to bridges or property. The observations made by the GEER team suggest that bridge abutments, buried utilities in earthen structures, and timber-framed buildings downstream of dams and other high-risk flood zones warrant additional considerations during design to increase resilience during extreme events.

The cone penetration test (CPT) has become one of the preferred methods of site characterization, particularly for large infrastructure projects, partly due to its simplicity and partly as a result of the development of reliable cone resistance-based correlations for footing design, pile design, and liquefaction resistance estimation. This paper presents a statistical methodology for estimation of optimal spacing between CPT soundings performed at a site in a way that is logical and easy to implement in geotechnical practice. The methodology quantifies the variability of a site in the horizontal direction through a horizontal variability index, which is a function of the spacing between soundings, the cross-correlation of cone resistances, and the difference in cone resistance trends between all pairs of soundings within the test site. The methodology is illustrated using CPT data obtained from multiple soundings performed at a bridge construction site in Lafayette, IN.

Engineering properties of fine-grained soils are quite complex. Primary properties, such as Atterberg limits, mineralogy and grain size, and secondary properties such as water content, density, consolidation/stress conditions, are extremely important in the geotechnical characterization of such soils. This note briefly quantitatively evaluates the correlation among fine-grained engineering properties such as Atterberg limits, soil activity, plasticity ratio, water content ratio, specific surface area, clay fraction, and undrained shear strength of remolded soils considering over 500 data from the literature. Data show that while a good relationship exists between plasticity ratio and soil activity, plasticity ratio cannot be related to clay fraction. Over an entire trend of data, it is possible to state that the undrained shear strength of remolded soils has an acceptable relationship with both liquidity index and water content ratio, that is, the water content related to the liquid limit.

Approach to site characterization and analyses are the twin pillars for geotechnical design, and therefore determine the cost efficiency of any project. Despite this, in many places in the United States, market competition and owners requesting multiple bids for geotechnical reports have reduced the scope of geotechnical work on projects over the years. To maintain an acceptable level of risk, this reduction in project scope has necessarily also increased the level of conservatism, particularly in foundation design. In this case history set in Salt Lake City, the combination of low-cost versus higher-cost site characterization and analysis for a large mixed-used structure are contrasted through the design process for a site with soft, compressible clayey soils interbedded with highly liquefiable silty and loose sandy soils. The case history illustrates the differences in design and resultant costs to the owner across a span of four different designers. The final design, based on higher cost investigations and analyses, resulted in significant savings to the project and the owner. The structure was instrumented to monitor settlement performance during and after construction. Not only does this paper show a case history in foundation settlement performance during construction on soft, compressible soils, but also demonstrates the effectiveness of higher geotechnical fees in saving construction costs. As a dual technical and business case history, the authors show that geotechnical firms can justify additional geotechnical engineering fees to greatly save owner costs.

Geological uncertainty is the changeability due to one geomaterial embedded in another, particularly at the boundaries between the different geomaterial layers. Spatial Markov Chains (spMC) and information entropy were used in this study to simulate subsurface geomaterials and to quantify geological uncertainty in two dimensions (2D) based upon spare borehole data. The proposed methods were illustrated using a bridge site in Wyoming. Results showed that the multinomial categorical simulation (MCS) model provided more accurate description of geomaterials as measured by an uncertainty quantification of 0.006 and a confidence ratio of 91.9%. The reduction of geological uncertainty does not always imply the need for additional boreholes when data are available from boreholes that are well-spaced within the site. However, if there is need for additional boreholes, optimized locations to reduce uncertainty can be determined. Thus, the proposed approach could also serve as a guide for designing a site investigation plan.

The piezocone penetration test (CPTu) is a commonly used method for geotechnical and environmental engineering site investigation. CPTu dissipation tests, which can be classified as monotonic or non-monotonic depending on the type of pore pressure dissipation they exhibit, provide data from which a soil’s coefficient of consolidation and hydraulic conductivity can be estimated. However, there remain limitations in interpreting CPTu dissipation tests—e.g., simplification to a one-dimensional problem, or applying methods developed for monotonic tests to analyze non-monotonic data—that affect characterization of interpreted soil properties. To examine the performance of interpretation methods and limitations of their assumptions, CPTu dissipation responses at the cone shoulder position (u₂) from field-measured and numerically simulated dissipation tests are analyzed and interpreted, according to four published methods. Numerical simulations of u₂ dissipation tests were performed with a direct axisymmetric penetration model and the MIT-S1 constitutive model for a range of overconsolidation ratios and hydraulic conductivity anisotropies. Interpreted values from each of the applied methods are compared for both field-measured and simulated data. Additionally, the performance of these methods in interpreting assigned model properties from numerically simulated data is examined. This study investigates two factors that affect interpretation of coefficient of consolidation from u₂ dissipation tests: non-monotonicity and two-dimensional pore pressure migration (radial and vertical). The results indicate that two-dimensional pore pressure migration contributes to CPTu dissipation, which is inconsistent with most interpretation methods’ assumption that vertical pore pressure migration is negligible, and that non-monotonic dissipation behavior is affected by vertical pore pressure migration. Additionally, the results indicate that non-monotonicity in dissipation responses negatively affects interpretation of assigned properties.

The cone penetration test (CPT) is commonly used to evaluate the in situ conditions of waste facilities, including tailings storage facilities and ash ponds, because it can measure near-continuous vertical profiles of loose and saturated materials that then correlate to various geotechnical engineering properties. Data collected from CPT soundings can be correlated to the in situ density which then allows engineers to evaluate the effective vertical stresses, perform storage capacity analyses, and evaluate the consolidation of materials. However, the existing density correlations were typically developed using data from natural soil deposits and, therefore, may not be applicable to waste materials such as tailings or coal combustion residuals (CCR). This paper evaluates the applicability of CPT density correlations for geotechnical exploration programs from several waste sites across North America that exhibit varying soil gradations and specific gravities. The in situ density is estimated using correlations to CPT data and is compared to measured densities from tube specimens. The correlated densities for tailings and CCR materials exhibit more variability than natural soil deposits. The existing correlations tend to underpredict the in situ density for finer and denser soils. Correlations to seismic measurements are not recommended as the variability is higher than correlations to typical CPT measurements. Recommendations for the fitting of site-specific corrections and future correlations are provided.

Representative piezocone penetration test (CPTU) soundings along with dissipation tests in structured Boston Blue clay (BBC) at the famous Saugus Station 246 site are used for a complete geo-characterization where strength, stress history, and flow parameters are interpreted using closed-form analytical solutions. The test site is underlain by an upper overconsolidated (OC) clay layer over a lower structured and sensitive normally consolidated (NC) layer. A modified hybrid spherical cavity expansion-critical state soil mechanics (SCE-CSSM) framework is utilized to obtain the operational rigidity index (I_R), effective yield stress (σ_p'), and undrained shear strength (s_uTC) for the upper OC layer and lower NC structured layer, whereas the coefficient of consolidation (c_vh) is evaluated using the piezo-dissipation results. The interpreted profiles of σ_p', I_R, s_uTC, and c_vh from CPTU soundings agree well with results from laboratory consolidation and triaxial testing.

Diatoms are single-celled organisms of various shapes and sizes typically found in lacustrine or marine environments. When diatoms die, the organic material decomposes, and the outer skeletons, frustules, settle and accumulate as sedimentary deposits. These soils, called diatomaceous soils, exhibit nontraditional behavior since the diatom particles are typically hollow skeletons composed of amorphous silica with intricately patterned and abrasive surfaces. Recent studies have shown that diatomaceous soils are challenging geomaterials since even a small proportion of diatom particles will notably affect engineering behavior. Furthermore, laboratory studies on diatomaceous soil mixtures have demonstrated that many engineering soil properties depend on the proportion of diatoms. For example, liquid limit and plastic limit increase as the proportion of diatom particles increases. Although the proportion of diatom particles relates to geotechnical properties, there are currently few published correlations to quantify this relationship. This research has two objectives: (1) to develop a method to characterize diatom particle proportion for natural diatomaceous soils; and (2) to investigate how these percentages relate to physical properties such as liquid limit, plastic limit, and plastic index. The soils for this project were sampled from southern and central Oregon and imaged using scanning electron microscopy (SEM) to obtain high-resolution images. These images were then analyzed using quantitative stereology to estimate diatom particle percentages. These proportions were compared to measured soil properties to evaluate the relationship for these natural diatomaceous soils. This investigation indicated that analysis of SEM images with quantitative stereology is a reasonable method to estimate the diatom proportion in soil. Additionally, the relationships between physical soil properties and diatom proportion of natural soils were reasonably consistent with the trends observed for laboratory mixtures of diatomaceous soils.

Two new parameters are introduced in this paper to provide methods of interpreting the widely used N-value obtained in accordance with ASTM D1586 methods. These new parameters are the Normalized N-value (NN) and the Residual Soil Index (RSI). These factors are helpful in determining if deposited or residual soil conditions are present in the subsurface. They are also helpful to determine if soil conditions are generally suitable for foundation loads or if rigorous methods of analysis are required. Examples of the calculation of these parameters are discussed in the text along with a suggested limiting value of the RSI.

Hurricanes produce large amounts of precipitation over short periods of time. This sudden influx of rainfall rapidly changes subsurface hydrological conditions. The increase in rainwater, or recharge, of the surficial aquifer happens significantly faster than that of the confined aquifer, resulting in a rapid increase of head difference. In Central Florida, a relatively thick impermeable soil (i.e., Hawthorn Group) layer is present between the surficial and confined aquifers. The increase in head difference causes internal soil erosion, often a catalyst in the creation of sinkholes. In this study, to better understand the rapid change of head difference, a temporal analysis of piezometric head before, during, and after a hurricane event was performed. Additionally, the change in lateral hydraulic gradient, measured between two adjacent piezometric sensors, was considered and investigated over the same time interval. This study was applied to the Wekiva Parkway SR46 connector project in Central Florida. The results from the analysis indicate that Sensor 1-3 location may be at or near an area of recharge. Based on an increase in hydraulic gradient and low sinkhole resistance ratio (SRR), Sensor 1-2 location has the highest potential for internal soil erosion.

The cone penetration test (CPT) is a widely used geotechnical tool, which provides excellent stratigraphic detail and information for estimating a wide range of soil properties. CPT consists of pushing at a constant rate an electronic penetrometer into penetrable soils and recording the resistance to the cone tip or cone bearing (q_m). The q_m values are utilized to characterize the soil profile along with measured sleeve friction and pore pressure. Cone bearing measurements at a specific depth are blurred or averaged due to q_m values being strongly influenced by soils within 10–30 cone diameters from the cone tip. This blurring of the true cone tip readings results in the inability to identify thin and low-bearing soils, which are masked by the properties of the adjacent soils. The q_mHMM-IFM algorithm was developed was developed to address the q_m blurring/averaging limitation. The q_mHMM-IFM algorithm implements a hybrid hidden Markov model and iterative forward modelling technique so that true cone bearing are obtained from the averaged/blurred q_m values. This paper demonstrates the performance of the q_mHMM-IFM algorithm by analyzing very challenging test bed simulations where thin soil layers are interspersed within uniform soils. It is critical to characterize a proposed algorithm capabilities by analyzing numerous test bed simulations prior to implementing on real data sets. It has been our experience in the industry that developed geotechnical signal processing software typically carries out minimal test bed simulations to verify an algorithms performance prior to implementing on real data sets.

Analyzing the pore size distribution is essential to understand the microstructural behavior of clayey soils. The objective of this study is to evaluate the effects of different drying techniques on the pore size distribution of Bentonite at two different hydraulic states by adopting the BET (Brunauer–Emmett–Teller) instrumental test. To represent two hydraulic states, corresponding to 1,121.6 kg/m³ dry density, 15% and 36% water contents are selected from the dry and wet of the compaction curve’s optimum water content. It is observed that outgassed specimens show higher mesopore volume compared to non-outgassed specimens. Alternatively, dry specimens exhibit more macropore volume than wet specimens. Also, outgassed specimens intend to have higher total pore volume compared to non-outgassed specimens. Thus, specifying a standard drying technique is vital to analyze the pore-size distribution of Bentonite at different conditions.

Highway slopes are susceptible to failure due to seasonal fluctuations of shear strength of high-plastic clay. Previously, wet-dry cycles have been evaluated primarily through laboratory studies. But these tests failed to simulate field conditions. In this study, Dynamic Cone Penetrometer (DCP) was used to measure the shear strength of a 45.7 m long highway slope for 13 months to get a better insight into these types of failures. The spatial variation of the slope was examined at its crest, mid-height, and toe. The field data were correlated with the laboratory unconfined compressive strength (UCS) test results, performed on the undisturbed samples. Results indicate that the Dynamic Penetration Index (DPI), which is a measure of penetration depth per blow, has an inverse relationship with UCS. In dry seasons, DPI values are higher, indicating a lower shear strength, whereas, in wet seasons, the opposite is true. For crest, mid-height, and toe of the slope, the coefficient of variation was 31%, 25%, and 15%, respectively; thus, shear strength fluctuated most at the crest, and consequently, most slope failures begin at the crest.

This study is focused on the experimental investigation of the coupled thermo-hydro-mechanical effects on transport properties of clayey soils. Glacial till specimens collected from a borehole at the University of Illinois at Urbana-Champaign (UIUC) campus were subjected to the effective mean stresses at their corresponding depths and the thermal gradient typical for a shallow geothermal system. The experimental results indicate the increase in permeability of glacial tills with temperature, mainly pounced for shallower specimens. The changes in material properties and dilation/compaction of normally consolidated tills are considered in the constitutive model that allows calculating the changes in porosity due to applied thermo-hydro-mechanical loading. The power law porosity-permeability relationships for glacial tills at different temperatures are established and indicate porosity sensitivity exponents’ values of approximately 15—similar to those for claystones.

This paper discusses the numerical performance of different explicit strategies used to integrate NorSand model (NS), an elastoplastic framework implemented to simulate static liquefaction in loose granular materials. Based on Critical State Soil Mechanics (CSSM) principles, NS captures the mechanical behavior of loose and dense soils by introducing state dependency and limiting dilatancy in the hardening rule. NS is integrated using an explicit algorithm based on Runge-Kutta-Fehlberg (RKF) methods of different orders in which numerical performance is inspected by solving (1) material point stress paths, and (2) finite-element analyses. After verifying the model implementation by comparing the soil behavior with a Visual Basic for Applications (VBA) spreadsheet, it is shown that the enhanced accuracy employed in higher RKF orders minimizes the substepping process of the constitutive integration thus resulting in faster calculation times.

The crushing of granular materials has a considerable impact on its engineering behavior. Simple anisotropic sand, SANISAND (SS) is a well-accepted model to simulate the response of sands. The main attribute of the SS04 model is the fabric aspect that can realistically capture the increased-pore water pressure upon stress reversal and with the same set of calibration constants, the model can predict the sand behavior at variable relative densities and confining pressures. One of the limitations of the SS04 model is an open-wedge yield surface that cannot predict plastic deformations in isotropic conditions worked by SS08. Both these models cannot predict the response of breakage. In the present study, two different versions of SANISAND constitutive models (SS04 and SS08) are modified and compared to quantify the particle breakage within the critical state context and bounding surface plasticity. The critical feature of modified models is to enhance the SANISAND model by incorporating the change in the critical state line (CSL) in the constitutive formulation to capture soil fabric evolution induced by monotonic loading. Proposed models mimic the experimentally observed responses of soils subjected to monotonic loading conditions, with reasonable accuracy. However, the amount of breakage accumulated in modified SS04 is significantly less than the modified SS08 model, for a fixed amount of strain. A final comparison of the modified models indicates that the breakage simulation feature of the proposed modified version of SS08 is better than the modified SS04.

Earthquake surface fault rupture produces complex patterns of shear rupture that are heavily influenced by soil inhomogeneity. This study analyzes the influence of inhomogeneous void ratio throughout the soil medium using the distinct element method (DEM). DEM captures the dilatancy and stress–strain response of dense and loose soils without the need for calibration of a constitutive model. Particle assemblages are prepared through a numerical pluviation routine in which loose and dense layers are achieved by pluviating particles with different frictional characteristics. Void ratio is measured within sub-volumes of the particle assemblages. The shear zone along the path of fault rupture is observed as a path of low-relative density and large particle rotations emanating from the bedrock fault. The mobilization of stresses in dense layers exhibited a peak stress followed by softening down to a critical state value, whereas the mobilization of stresses in loose layers monotonically rose to its critical state value. Complex patterns of rupture resulted from the evolution of different soil responses in the layered soil deposit.

In recent years, natural hazards involving environmental flows and large mass movements, such as landslides, debris flows, and mudslides, have significantly increased in frequency due to the influence of global warming and climate change. Understanding the hydro-mechanical interaction of free-surface flow and saturated soil is, therefore, essential for designing geotechnical infrastructure in the upcoming decades. Such interaction phenomena exhibit challenging complexities not only mechanically but also from the numerical point of view. In the current work, the Material Point Method (MPM) is chosen as the numerical method to simulate the multiphase fluid-soil coupled problems. Even though the original formulation of the MPM, which assumes explicit dynamic time integration, has been proven to be successful in simulating many large-deformation problems, the method still suffers several drawbacks in efficiency accuracy. The semi-implicit version of MPM has been developed to circumvent these issues, which reduces pressure oscillations and increases the allowable time step size. Incorporating this technique to model two layers of materials, that is, the immiscible solid skeleton and the fluid phase, the proposed method can produce a significantly accurate coupling, yet easy implementation for advanced material models to tackle the problems of interest. Practical examples of this approach are limitless, which include fluidization, erosion, sedimentation, and seepage flow, as well as many other offshore applications.

At the same effective stress, shear strength of consolidated clays is a function of the stress history. Normally consolidated clay specimens tend to contract upon shearing while overconsolidated clays tend to dilate. Moreover, overconsolidated clays have a peak shear strength while normally consolidated clays plateau to their critical state. In this study, two-dimensional (2D) discrete element method (DEM) simulations for kaolinite at different stress histories are presented. Clay particles are modelled as rigid rods (clumps) in a two-dimensional framework, with different sizes replicating the actual particle size distribution of the kaolinite used later for model validation. The nonlinear nature of contact between clay particles is simplified by introducing linear springs at the particles’ contact to simulate van der Waals attractive and double layer repulsive forces. A series of numerical simulations at different stress histories and effective stresses is presented. The observed shearing behavior at different stress histories is discussed in light of microstructural changes before shearing. Results suggest particle orientations, and therefore the physico-chemical forces prior to shearing might have minimal impact on shear strength, while the void ratio is the main factor controlling the shearing behavior.

Soft mudrocks have low permeability and are mostly treated as sealing geological formations. Clay-rich soft mudrocks are also classified as the transversely isotropic (TI) material due to the intrinsic preferred fabric orientation. The TI elastic properties of soft mudrocks are highly dependent on the containing mineralogical compositions and clay fractions. Thus numerical modeling is necessary to estimate the behavior of soft mudrocks. In this study, a two-dimensional homogenization model is employed to assess the elastic moduli of soft mudrocks. Clay-water composites are treated as the hosting matrix, and non-clay minerals are placed in the REV as the inclusions. The inclusions are placed randomly in different sizes. In order to consider the partial flexibility between the non-clay minerals and clay-water composites, an imperfect boundary is defined between the inclusions and matrix using the eXtended Finite Element Method (XFEM). The periodic boundary condition is imposed on the REV, and the homogenized anisotropic elastic moduli of rocks with different clay fractions are estimated. The numerical results were validated using published experimental data on the static TI elastic properties of soft Colorado shale samples. The results show the predictable decreasing trends in elastic modulus of soft mudrocks with increasing of the clay fraction.

Discrete Element Method Modeling is used in this study to simulate simple shear tests and evaluate the efficiency and effectiveness of two different specimen cap types. Slippage can occur along the top and bottom boundaries in simple shear testing, causing inefficient transmission of shear forces through the sample and non-uniform stresses and strains to develop. Therefore, appropriate boundaries are required to ensure the efficient application of forces. To study the effects of boundaries, a series of monotonic laminar ring, direct simple shear tests with two types of top and bottom caps are modeled. The evolution of shear forces on each type of boundary is analyzed and the particle rotations are visualized to assess the influence throughout the specimen. Different boundaries display evidently distinct performance in computational efficiency, force transmission, and particle rotations.

The self-weight consolidation testing of slurry material in a centrifuge environment reduces the testing time significantly and simulates better field stress conditions. However, variation in the centrifuge acceleration with the depth of the model poses a challenge in interpreting the results. The settlement behavior of a prototype of fixed height was predicted from numerically simulated centrifuge consolidation test data using the scale factors corresponding to various effective-radii and model base values. The predicted settlement behavior was compared with the simulated prototype settlement. The ultimate settlement was under-predicted using the constant-N as the scale factor. The maximum error in ultimate settlement with base N was 3.74%, which was much less compared to the other cases where the model height to centrifuge radius ratio was kept below 0.25.

Damage of unconsolidated sandstone in drilled hydrocarbon wells can lead to the production of sand particles resulting in erosional damage to equipment and costly repairs. This paper focuses on comparing the standard material point method (MPM) with a novel material point method (cut-mesh MPM) formulation for modeling the onset and propagation of sand production in wellbores. Utilizing isoparametric elements provides some improvements over rectilinear elements for arbitrary and complex geometries, but these elements are still prone to quadrature errors and numerical instabilities as elements become partially filled due to large deformations and the erosion process. Combining cut-mesh MPM with isoparametric elements provides an improved approach for modeling the sand production process. Accurate predictions of downhole wellbore breakout and cavity damage is critical to determine both the onset and magnitude of sand production. Both standard and cut-mesh MPM are used to model a thick-walled cylinder (TWC) collapse test of Castlegate sandstone TWC. Final geometry and cumulative sand production mass indicate that cut-mesh MPM provides increased numerical stability relative to standard MPM when modeling erosion. Although this novel MPM formulation is relatively more stable than standard MPM, both methods struggle to capture the sharp localization of the physical TWC sample. Likewise, both standard and cut-mesh MPM are unable to reproduce the magnitude of sand production mass observed in the physical TWC sample. Complexities such as particle arching, strength anisotropy, and material fracturing are not modeled by standard or cut-mesh MPM; these complexities represent some of the possibilities for why numerical outputs are unable to match observed physical samples.

The aim of this study is to identify thermally induced changes in the diffused double layer thickness around clay particles. The temperature dependency of the diffuse double-layer thickness has been questionable over the past decades. The modified Boltzmann equation suggests that the thickness of the diffused double layer is proportional to the square root of temperature. However, other contradicting arguments exist in the literature. Molecular dynamics (MD) is used to simulate temperature effects on the thickness of the diffused double layer surrounding kaolinite clay particles. The MD simulation considers a 3D clay specimen using Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS). Silicon tetrahedron and aluminum octahedron sheets are built, and simulations under different temperatures ranging from 273 K (about 0°C) to 313 K (about 40°C) are performed. The results show that temperature changes have a significant impact on the energies of the system, which implies considerable changes in diffused double layer thickness around kaolinite clay particles.

Bio-mediated techniques are among biogeochemical processes in subsurface that have been introduced as alternatives to conventional methods for soil improvement. These processes can alter hydraulic properties of the subsurface through a complex veriety of coupled processes including the interaction of biomineral–biogas–biofilm with the solid matrix and pore structure of the soil. A clear understanding of these obscure interactions is critical to study the impact of bio-geochemical processes on the hydrology and predict reactive transport phenomena within the treatment zones. In this study, a 3D pore network model is extracted by CT imaging from a sandy soil sample. Various scenarios resembling different biogeochemical products and contents are numerically assigned into the networks. Simulations including evolution of pore-scale characteristics and Representative Elementary Volume (REV) scale porosity–permeability relationships are investigated. The results show that the hydraulic properties of bio-treated soils are dramatically affected by the spatial distribution, heterogeneity, and pore-habit of the products of bio-mediated processes.

Extreme weather events are a main cause of landslides in recent years. Real-time control of groundwater tables in slopes can help protect earth slopes in areas prone to flooding. Though subsurface drainage wells equipped with a pumping system is an efficient way to lower the groundwater, it has been mostly employed in short-term projects due to the high-operational costs in labor and energy. To reduce these operational costs, this paper investigates the idea of an autonomous pumping system enabled by Deep Reinforcement Learning (DRL), which is a subfield of machine learning for automated decision-making. Such a system can dynamically adapt its response to rainfall events by controlling the pumping flow rate, and more importantly, can improve the pumping policy over time. To prove the idea of the autonomous pumping system, a seepage analysis model was implemented using a partial differential equation solver, FEniCS, to simulate a lab-scale geo-system, that is, a slope equipped with a pump and subjected to rainfall events, which served as the virtual environment for the reinforcement learning. A Deep Q-learning Network (DQN), that is, a DRL agent, was implemented to learn the optimal control policy based on the trial and error process of the system to achieve the desired objective. This agent was trained to learn how to control the pump’s flow rate to keep the groundwater close to the target level during different rainfall events. A reward function was defined to evaluate the state of the groundwater, which could affect the next action taken by the agent. The goal of the DQN is to find a policy that maximizes the received reward. The training was carried out from scratch without human interventions. Aiming at binary control, the agent learns whether to turn on/off the pump based on the rewards constructed with the distance of the water at the time of decision and the target level. The results showed that a DRL can learn how to control a pump to maintain the water level in a binary control mode, which may point out a promising direction for establishing intelligent geo-systems. Such autonomous control of groundwater can help mitigate landslide hazards as a long-term geotechnical solution.

The unified state parameter model for clay and sand (CASM), proposed in 1998, showed powerful capabilities in representing the behavior of both clayey and sandy soils. However, calibrating some of the model parameters is still an issue for practitioner engineers. Recently, the modified state surface approach (MSSA) was proposed to represent the unsaturated soil’s behavior. This approach was successfully used to represent many unsaturated soils’ behavioral features. In this paper, the MSSA is used to mathematically derive surface equations for the CASM. The derived surfaces can be used to easily calibrate the model parameters and to represent the soil behavior under isotropic and general stress conditions. To validate the model surfaces, first, they were used to predict the behavior of several soils and compare them with the available results from the literature for the same model. Then, a parameter calibration algorithm is proposed, and step-by-step procedures are illustrated. Generally, using the MSSA made it simple and straightforward to calibrate the CASM model parameters.

The Millennium Tower is a pile-supported 58-story building constructed in San Francisco, California, between 2005 and 2009. As a result of time-varying stress changes in an over-consolidated clay layer below the pile tips, the foundation has settled and tilted at variable rates. Settlement and tilt have been measured since 2006 and 2009, respectively. As part of a broader analysis of this case study, we describe here three-dimensional simulations of stress increases in foundation soils, groundwater changes beneath the tower, and foundation settlement and tilt. The analyses are performed in FLAC3D using a calibrated soft soil creep model to capture the effects of secondary compression. Stress changes in the underlying clay layer are computed using the Tower self-weight and time-varying dewatering at the Tower and adjacent sites. Groundwater changes with time and foundation movement are compared to observations with reasonable agreement. Companion papers present the case study and one-dimensional settlement analyses.

Permeability variations caused by fines migration could have a significant impact on the geomechanical response of geological reservoirs during energy and environmental operations. This study presents a fully coupled model that integrates the poroelasticity theory with fines migration phenomenon in saturated porous media under isothermal conditions. The formation of interest contains fine particles situated on the solid surface of a saturated porous skeleton. The maximal retention function adopted in this study is take to be a function of spatiotemporal fluid velocity alterations. Findings show a notable impact of the latter on in situ permeability, pore pressure, and stress/strain alterations, specifically at wellbore vicinity.

The significant shortage of land due to rapid urbanization and population growth has been triggering the development and utilisation of underground space. The shield tunnelling is an increasingly popular alternative to open-cut excavation for underground space development due to its highly efficient and minimal ground disturbance. Conventionally, the performance of tunnelling was evaluated based on laboratory experiments, which are not cost-effective, time demanding, and involving many uncertain variables. Further, this leads to difficulties to measure the earth pressure acting on the cutting face and reproduce the real tunnelling process. Therefore, researchers have been using the discrete element method (DEM) as an alternative tool that can capture the discrete nature of the soil and the soil fabric (affecting the stresses in soil) and simulate their impacts on the tunnelling process. Most DEM studies in the literature have used spheres as representative granular material to reduce computational demands. However, most granular materials, such as sands, are not rounded but possess angularity features; and most DEM studies in tunnelling often ignore the effect of particle angularity. In this study, both the spheres and clustered particles are, therefore, adopted to evaluate the effect of particle shape on the stresses in the soil during the shield tunnelling process. This will provide a better understanding of the evolution of the stress at the interface between the cutterwheel and angular soils.

A coupled SPH-DEM scheme is employed to study flow failure of a liquefiable sand layer overlain by an impermeable crust. In this technique, DEM is used to model soil particles and the fluid is simulated using SPH. The coupling between the phases is achieved through well-known semi-empirical relations. The proposed approach is used to analyze the seismic response of a mildly sloping deposit with an impermeable crust. Flow failure was observed during the seismic excitation of the model, marked by void redistribution and significant dilation of a thin layer at the liquefied layer surface as well as progressive accumulation of large shear strains even after the end of loading.

Timely detection of hidden potential solution cavities subject to adverse subsurface conditions is a challenge, especially when located under active pavement areas. Site subsurface conditions for this study consisted of the subgrade layer reinforced by the existing geogrids overlying deeper untreated thick gypsum backfill. The tidal groundwater and/or rainfall infiltration caused dissolution of the gypsum, creating large voids in the subgrade. This paper describes how the use of Finite-Element Method (FEM) analyses provides a practical approach to help improve the prediction of performance for a unique Load-Transfer Platform (LTP) design. Considering various potential void diameters under applied vehicular live loads, parametric studies were conducted using the FEM approach to determine key design values (i.e., resulting forces on geogrid layers and a maximum settlement). Subsequently, by correlating surface settlement measurements to tensile load on each geogrid layer, project settlement criteria were developed to help facilitate scheduling of future pavement repairs of the LTP based on long-term effects on capacity of the geogrid layers.