Geo-Congress 2020: Modeling, Geomaterials, and Site Characterization

Soil particles that have been deposited through water or air generally align their largest projected surface area normal to the depositional direction, which generates a cross-anisotropic fabric of granular soils. Researchers have used both two-dimensional (2D) and three-dimensional (3D) images to determine scalar fabric parameters of granular soils, including void ratio, coordination number, and average branch vector length. This study aims to evaluate the accuracy and effectiveness of 2D images to characterize fabric in 3D soils based on scalar parameters. The X-ray computed tomography (X-ray CT) is used to reconstruct the 3D volumetric images of three air-pluviated sand specimens, including crushed limestone, Griffin sand, and glass beads. Then, six slices are obtained by vertically cutting the 3D volumetric image in an angle increment of 30 degrees. The 3D and 2D images are analyzed to determine scalar fabric parameters. The results show that coordination numbers and average branch vector lengths computed from 2D images underestimate these values in 3D granular soils. The void ratios computed from 2D images vary a large range depending on slicing directions, which cannot provide reliable fabric characterizations for 3D granular soils.

Impact penetration into soils is one of the most challenging phenomena to model using numerical techniques due to the very rapid large-deformations and water-soil-structure interaction problems involved in the process. In this work, portable free fall penetration testing (FFP) in dry and saturated sands is modeled using the material point method (MPM). MPM is a powerful tool for large-deformation applications in history-dependent materials. A parametric analysis is performed to understand the influence of the soil stiffness and the water excess pore pressures produced during the impact. The effect of the sand stiffness is studied by modifying its Young’s modulus, and the effect of the water is considered by comparing a fully dry model with a fully coupled hydro-mechanical model. The results indicate that the stiffness of the sand strongly controls the appearance of a general bearing capacity failure, which produces deceleration responses with more than one peak, dissimilar to physical tests. In the case of fully saturated sand, the penetration depth is lower than for dry sand with the same properties and the kinematical response of the FFP is consistent with experiments. The results are promising and encourage further development of the simulations.

In this work, we configure a fully coupled hydro-mechanical finite element model to study the interaction between fault zone and injected fluids. This generic model simulates fluid injection into a porous reservoir near a preferentially oriented normal fault that extends from the sedimentary layer into the basement. We use cohesive zone elements to characterize the damage initiation and propagation associated with the reactivation and slip of fault and incorporates the degradation of friction angle into the slip process. Comparative analyses are carried out to reveal the influences of the distance between injection well and fault on fault reactivation. Through this model, we observe the coupled effect of injection rate and injection distance on the onset of fault reactivation and the ensuing fault slip. High volume injection at a close field site may exert a more significant perturbation on the stress state of the fault. Our study highlights the importance of injection site selection and injection activity plan in minimizing the likelihood of induced seismic events.

Accurate modeling of an excavation unloading process is challenging due to the complex interactions and couplings between soils and structures which are not easily captured unless robust geotechnical and structural models are used. OpenSees is an opensource numerical platform capable of modeling complex geotechnical and structural systems integrated in a single model using fully coupled fluid-solid and nonlinear element formulations to model partially drained conditions and post-plastic structural behavior. This paper presents general guidelines for future studies of deep excavations in OpenSees along with a proposed quasi-static analysis needed to solve static stage construction-based geotechnical problems under drained, partially drained, or undrained conditions.

The material point method (MPM) is a hybrid Eulerian-Lagrangian approach capable of simulating large deformation problems of history-dependent materials. While the MPM can represent complex and evolving material domains by using Lagrangian points, boundary conditions are often applied to the Eulerian nodes of the background mesh nodes. Hence, the use of a structured mesh may become prohibitively restrictive for modeling complex boundaries such as a landslide topography. We study the suitability of unstructured background mesh with isoparametric elements to model irregular boundaries in the MPM. An inverse mapping algorithm is used to transform the material points from the global coordinates to the local natural coordinates. Dirichlet velocity and frictional boundary conditions are applied in the local coordinate system at each boundary node. This approach of modeling complex boundary conditions is validated by modeling the dynamics of a gravity-driven rigid block sliding on an inclined plane. This method is later applied to a flume test of controlled debris flow on an inclined plane conducted by the United States Geological Survey (USGS).

Granular materials may exhibit solid- to fluid-like behaviors under different flow conditions. This makes granular flow an interesting topic for research, which has gained significant attention in the recent years. In particular, the collapse of granular columns within dynamic/rapid and slow/quasi-static flow regimes has been the subject of various experimental and numerical studies and provided invaluable insights into phenomena such as landslides, avalanches, active movement of retaining walls, etc. In this study, the axisymmetric collapse of granular columns has been numerically investigated using three-dimensional (3D) smoothed particle hydrodynamics (SPH) models. The elastoplastic behavior of granular materials is modeled through using Drucker-Prager constitutive model with non-associated flow rule. Quasi-static and dynamic collapses of granular columns with a wide range of initial aspect ratios are modeled using the developed model. The flow was triggered by removing or expanding the cylindrical wall for dynamic and quasi-static flow types, respectively. Results of simulations are validated against experimental data on dynamic collapse of granular columns. Moreover, the developed models provide the means for a comprehensive comparison between quasi-static and dynamic axisymmetric collapses of granular columns, in terms of collapse pattern, final deposit profile, and energy dissipation. The results reveal qualitative similarities between these types of collapses, emphasizing the importance of the initial aspect ratio of the column on deposit morphologies, collapse pattern, and energy dissipation.

In the present study, an attempt is made to evaluate the ultimate pullout capacity of the vertical helical plate anchor embedded in clay with a number of geometrical configurations using the limit analysis based on the finite element method. Ultimate pullout capacity (q_u) of single and multiple helical plate anchors are determined using numerical analysis considering the two-dimensional axisymmetric model and the stress-controlled loading in the present work. Evaluation of the ultimate pullout capacity of the single helical plate anchor is determined with varying embedded depth (H). Also, the ultimate pullout capacity of multi-plate anchors are evaluated using a detailed parametric study with the consideration of parameters namely numbers of plate (n), spacing between consecutive helical plates (S) while keeping the diameters of the helical plate (D) and anchor shaft (d) constant. The present study underlays the optimum H/D and S/D ratios for single and multiple helical plate anchors, respectively, and establishes a simplified equation for the estimation of q_u for a multi-plate helical anchor. Additionally, this study also examines the development of failure surfaces with varying embedded depth for single plate anchor and the interference of failure surfaces in the soil for the multi-helix plate anchors with the variation of S/D ratio.

The analysis of the stability of slopes using the limit equilibrium method largely depends on the use of an adequate procedure for finding the position and shape of the critical slip surface. Critical slip surfaces have been traditionally determined using brute force techniques that rely on assumptions regarding the shape of the slip surface, thereby imposing considerable constraints. Several optimization methods have been proposed in the literature to improve the search procedure for critical slip surfaces. Unfortunately, most research involving optimization methods has been confined to two-dimensional analysis. This paper examines the use of an optimization technique to different slope stability problems in three dimensions. The presented results show that the procedure is capable of locating a lower minimum factor of safety when compared to conventional approaches, even if the initial arbitrary slip surface adopted for the optimization procedure is not close to the converged slip surface. It was also demonstrated that the optimization procedure is capable of identifying composite shapes produced by the presence of a weak layer. The shape of the critical slip surface obtained using the optimization procedure was shown to deviate from an ellipsoidal shape when conditions such as weak layers of material anisotropy are present.

This paper presents numerical analyses of one-dimensional heat transfer in layered saturated soil with effective porosity and steady fluid flow using the numerical model HT1. The model characterizes the soil using separate columns to represent the solid matrix and mobile pore fluid components, and a series-parallel approach to model soil thermal conductivity. The model accounts for advection, conduction, and thermal mechanical dispersion assuming local thermal equilibrium between solid and fluid phases, and has the capability to analyze the effects of each mechanism separately. Numerical simulations are presented to illustrate the effects of effective porosity, discharge velocity, and layer heterogeneity on heat transfer behavior. Numerical solutions and analytical solutions are in excellent agreement.

The increasing use of the underground spaces in the urban areas has driven many researchers to deepen the knowledge on the effects of deep excavations on nearby properties. Earthquake hazards to utility systems become more and more important with the level of urbanization. The obligation to preserve services after an earthquake becomes more critical every day. Excavation-induced ground movements are generated by unbalanced forces due to the removal of soils within the excavation zone which could be greatly intensified if an earthquake is occurred. If the ground deformation is too large, neighboring facilities may develop cracks or damaged. Therefore, investigation of the seismic condition of adjacent properties in close proximity to deep excavation is required to avoid such damages. The main purpose of the present study is to investigate the dynamic performance of a buried pipeline alongside a deep excavation by ABAQUS program. A series of three-dimensional (3D) and two-dimensional (2D) finite element (FE) analyses are performed and the results, in terms of pipe normalized tensile strain, are plotted in dimensionless figures to evaluate the dynamic response of buried water pipe. The results show that the pipe seismic performance is a function of its position against the wall.

Limit equilibrium methods have been used for many years in the design of geotechnical structures, however they have a number of limitations and may miss critical failure mechanisms, leading to imprecise stability predictions and potentially requiring larger tailored safety factors to compensate. However, alternative, more accurate general-purpose numerical tools such as the elasto-plastic finite element approach have tended to be computationally costly and labour intensive, and generally find only a single, critical, failure mode, whereas engineers may wish to test the likelihood of a range of failure mechanisms forming. In this paper it is demonstrated that both these issues can be addressed via the use of computational limit analysis (CLA). CLA is a numerical tool that allows the user to determine rapidly and directly the ultimate limit state for a general problem geometry without the need to iterate or time step to a solution. This paper demonstrates how CLA can be used in the context of limit state design approaches such as LRFD. It then illustrates how a CLA approach may be carried out for a range of example foundation and retaining wall problems and compares and contrasts the process with conventional limit equilibrium approaches. The CLA technique discontinuity layout optimization, which is able to directly generate slip-line mechanism solutions of a form similar to those seen in many limit equilibrium solutions, is used to generate the results described.

Compression of aquitards has been widely accepted as the source of land subsidence considering the high compressibility of clay layers in aquitards compared with that of sand in aquifers. However, observational data of land subsidence in Yangtze River Delta, China, indicates that the compression of aquifers is comparable to that of aquitards. Compression of aquifers would result in the decrease of void ratio of sand in aquifers during pumping, which can cause reduction both in permeability and compressibility. A coupled model was proposed in this study to consider the change of permeability and compressibility during pumping by correlating the water level decline with both the permeability and compressibility of the aquifer layers. Finally, a pumping test conducted in Shanghai was used to verify the effectiveness of the proposed method.

The single particle uniaxial compression test has been widely used in the particle-scale breakage research. However, due to the rapid brittle breakage of particles, the failure mechanisms are not well observed. Remarkable advances in the high-speed imaging technique facilitate to observe the rapid and dynamic process of the particle breakage. This paper presents a novel testing system consisting of a single particle uniaxial loading frame and a high-speed video camera. The high-speed camera captures the rapid crack initiation and propagation process in gravel particles under uniaxial compression. A digital image correlation technique (DIC) is used to analyze captured video to determine displacement and strain fields during fracture initiation and propagation processes of gravel particles. This research verifies the feasibility of using high-speed imaging and DIC techniques to analyze particle breakage processes.

The railway industry has experienced enormous developments in recent history due to the emergence of high-speed trains, increasing number of passengers, and travel comfort. These developments require more efficient railroad design and reduction in maintenance costs. For optimizing the track lifetime and prediction of maintenance time, comprehensive understanding of the mechanical behavior of ballast material is required. The large particle size of the ballast material needs a unique testing facility to represent the proper behavior of the material in the laboratory. To better understand the shear behavior of the ballast material, a series of large-scale monotonic direct shear tests (DST) has been performed on crushed granite material at Texas A&M University laboratory. The test results revealed a nonlinear failure envelope for the material. It is shown that the friction and dilation angle varies nonlinearly with the normal stress.

To better understand the cone resistance mobilization mechanism in sands and its dependence on particle crushing, accurate, and precise quantification crushing of sand particle near the cone is necessary. This paper presents a methodology for the quantification of crushing of sand near the base of a cone after a cone penetration experiment. The developed methodology includes a detailed sand sample collection procedure based on agar-impregnation technique. The agar-impregnated samples are scanned using an X-ray microscope, and then the collected 3D tomography data is analyzed to obtain the distribution of crushing in the sample. The developed methodology is demonstrated using a sample collected from a cone penetration experiment carried out in dense sand. The penetration experiment is carried out in a half-cylindrical calibration chamber equipped with digital image correlation (DIC) capabilities. The crushing data are complemented by the displacement and incremental strain fields obtained from the DIC analysis.

Cyclical temperature changes occurring during seasonal freezing and thawing cycles significantly impact the moisture content and matric suction of subgrade soils, contributing to severe damage to granular roadways during spring thaws. Monitoring of these data in the field can play a significant role towards development of accurate and reliable freeze-thaw prediction models. In the present study, a weather station was installed along with an extensive network of 80 subgrade temperature, matric potential, and moisture content sensors below a granular-surfaced roadway for long-term monitoring. The subgrade sensors were installed over a range of depths up to 213 cm (7 ft) in five boreholes located under the centerline, shoulders, and quarter points of the roadway. Disturbed and intact soil samples from the site were collected and tested to determine soil index, thermal, and hydraulic properties of subgrade soils. This paper presents preliminary analyses of the in situ temperature, soil moisture, and matric potential distributions under the roadway, which are found to follow similar trends in general but exhibit unsymmetrical variations across the boreholes, which may be due to differences in surface boundary conditions, compaction ratios, and soil profile changes. The matric potential and water content values were found to decrease suddenly near the freezing point, indicating the start of soil water freezing. Finally, data from the installed weather station was compared to the air temperature and wind speed measurements from the nearest road weather information system (RWIS) stations. The air temperature values generally agreed, indicating that the RWIS data can be interpolated to obtain the site temperatures with reasonable accuracy, but wind speed did not provide similar agreement and requires further analysis.

This paper presents the prospect of 3D printing technology to generate artificial soil analogs with the goal of modeling the mechanical behavior of coarse-grained soils. 3D X-ray CT scans of natural angular and rounded sand particles have been used to generate angular and rounded particle analogs using the polyjet 3D printing technology. A comparison of the scanned natural sand particles and the 3D printed particles demonstrates the ability of 3D printing technology to reproduce the shape and size of the sand particles. The results of oedometer compression tests on the angular and rounded natural and 3D printed particles are used to demonstrate the effect of constituent material (i.e. quartz versus polymer) stiffness on the measured soil compressibility and investigate the normalization of the response using the Hertz contact theory. The results provided in this paper also include comparison of the small-strain moduli–mean effective stress relationship obtained for the natural and 3D printed soils. This paper illustrates the potential use of 3D printed analogs to model the mechanical behavior of coarse-grained soils and identifies future research needs for implementation of the proposed normalization scheme within the critical state soil mechanics framework.

Fiber-optic sensing systems embedded in soil are widely used to detect surrounding events via wave propagation through the soil media. Sensor cable performance is likely a function of coupling between the sensor and the surrounding soil. The purpose of this research is to evaluate the friction resistance between the cable sensor and the confining soil under controlled laboratory conditions, as greater resistance can correlate to better coupling. The cable used for this study was a 0.5-in. diameter industry standard, armored, 24-strand fiber-optic cable with a rubber-coated jacket. Gravel, sand, clay, and flowable fill were tested to illustrate geological variability of the soil-sensor characteristic behavior. To assess the pull-out stress, a test apparatus consisting of an acrylic box with 6-in. x 9-in. x 12-in. interior dimensions was designed for this study. Openings on the two 6-in. x 9-in. faces allowed the cable to pass through, 3-in. from the bottom and side edges. Soil moisture contents and densities were selected to match field conditions. The cable was axial strained at a rate of 0.126 in. per minute. The peak strength and residual pull-out strengths were monitored and recorded using a load-cell and a sampling rate of 2 kHz. Results showed the soils had peak resistances between 2.0 and 5.3 psi. The three flowable fill specimens varied greatly, resistances ranging between 30 and 90 psi along the cable.

Microparameters of the clay component of an earth fill dam need to be identified in order to develop a reliable discrete element landslide model. To characterize clay microparameters, a calibration process of matching the simulated and actual undrained consolidated triaxial test results were performed. Linear parallel-bond model was used to describe the interactions of clay particles. The microparameters calibrated to match the real clay behavior were particle stiffness, friction, bond stiffness, and bond strength. Sensitivity analysis revealed that bond stiffness and bond strength dictate the peak stress behavior of the numerical model, while particle stiffness and friction influence its critical-state stress behavior. The designed calibration methodology based from the sensitivity analysis results was able to identify a suitable set of microparameters that can simulate the real behavior of clay. Integrating the calibrated microparameters to the numerical model yielded good agreement between the measured and simulated stress-strain relationships of clay at different consolidation pressures.

In recent years, the use of unconventionally large aggregates for subbase layer construction has become popular. Such aggregates generally require less crushing than conventional size aggregates; therefore, the use of such aggregates can help to achieve energy savings and improved pavement sustainability. The engineering properties of aggregates greatly depend on the particle size distribution; therefore, size characteristics of aggregate particles must be well known. Sieve analysis may not be practical for unconventionally large aggregates due to the limitations of the existing test apparatus. In this study, stereophotography, a digital imaging technique, was evaluated as an alternative to sieve analysis to determine the size characteristics of aggregate particles. Sieve analysis and stereophotography were performed on an unconventionally large aggregate material. Their results were compared and it was concluded that the digital imaging technique was a very useful approach for size characterization of aggregate particles.

Granular roadways deteriorate over time due to both external factors (repeated roadway traffic loads and precipitation) and internal factors (weak subgrade soils, poor drainage, and low quality gravel/rock materials). As a result of these factors, granular roadways experience a significant amount of gravel loss during their lifespan. This is one of the main engineering challenges associated with maintaining such roads. Therefore, it is very important for engineers to be able predict annual gravel loss, to enable more reliable predictions for maintenance budgets. A gravel loss prediction model could help predict the amount of roadway surface materials expected to be lost after a given time, and therefore, to a greater extent, indicate to engineers the expected amount of materials to be purchased for the upcoming fiscal year. This tool can play a vital role in making proactive budgetary decisions for roadway maintenance. Existing gravel loss prediction models have mainly been developed to study the roadway material declination patterns on one or more segments in a roadway system. However, section-based gravel loss prediction models may not always be suitable to make network-level material declination predictions, because these models often require site-specific information which may lead to biased results caused by local calibration. In this study, granular road condition and performance data were collected from Iowa counties, and historical information on factors impacting roadway deterioration were obtained from federal government databases. Historical trends of daily traffic and precipitation variations, along with gravel/rock material quality test reports for quarries and soil test reports for counties, were analyzed to determine county-level representative values for each of those factors that contribute to granular road deterioration. Then the system-level roadway gravel loss was modelled using data from a full factorial experimental design. Multiple linear regression (MLR) analysis was also conducted considering county-level averages of daily traffic, precipitation intensity, gravel/rock material quality, and subgrade soil plasticity index as influencing variables. Out-of-sample data prediction and accuracy of fitted models were assessed using cross validation. The developed model can act as a standalone program because site specific data is not required to run the model and therefore, it provides the local agencies with a cost efficient annual gravel loss approximation tool.

Vehicle traffic loading induces a heart-shaped stress path in deviatoric stress space [τ_zθ to (σ_z-σ_θ)/2], causing the rotation of principal stress direction acting on a soil element. A conventional triaxial test is not capable of applying the principal stress rotation induced by heart-shaped stress path and therefore, is not able to evaluate the behavior of soils accurately under traffic loads. However, a hollow cylinder test can simulate heart-shaped stress path imposed by traffic loading. In this study, the effect of heart-shaped stress path on the vertical deformation behavior of sand-clay mixture including 20% of clay by mass was experimentally investigated through hollow cylinder test. The tests in this study were conducted at three stages: i) saturation, ii) consolidation, and iii) shearing. The specimens were first saturated until Skempton’s B≥0.95 and then consolidated with K₀=0.5. Thereafter, the specimens were sheared under cyclic loadings involving vertical stress and shear stress. Experimental results indicate that the principal stress rotation induced by traffic loading significantly influences the permanent strain development in sand-clay mixture.

Calcareous sands, comprising higher than 50% calcium carbonate, are mostly located between latitude 30°S and 30°N. The engineering properties of calcareous sands differ from those of clays and silica sands due to the high particle angularity and in situ void ratios. Investigation of calcareous sands properties and stress-strain response are required for the design and long-term maintenance of offshore infrastructure including piers, bridges, and offshore renewable energy structures. In this research, calcareous sands from Puerto Rico are investigated to determine the monotonic stress-strain response and how increasing severities of particle damage and crushing affect loading behavior. To accomplish this, several advanced laboratory tests were conducted: 1) triaxial tests (CU) were utilized to investigate the monotonic stress-strain behavior; 2) oedometer tests, providing the one-directional compression load for sand crushing. The calcareous specimens were tested under various confining pressures (σ₃) and with increasing percentages of crushed material.

In this study, the shear strength behavior of limestone waste was evaluated to determine its possible application as an embankment material. Direct shear tests were performed under a fully saturated condition. Limestone waste was mixed with conventional soil and was proportioned at 0% (S1), 20% (S2), 40% (S3), 60% (S4), and 100% (S5). Samples were prepared to have 90 to 95% relative compaction. Based on the results, cohesion is directly proportional with the limestone percentage while the internal friction is inversely proportional with the limestone percentage in the blend. As the percentage of limestone increases the angle of internal friction decreases. The cohesion values ranged from 0 to 48.42 kPa. On the other hand, the angle of internal friction ranged from 31.67° to 46.53°. Modified hyperbolic model was applied to predict the stress-strain and volumetric strain-shear strain response of the blended materials. Based on the results, the model can provide a good approximation of the stress-strain response of the samples that showed a ductile failure and compressive volumetric strain. However, the model cannot properly predict the stress-strain response of materials with brittle failure and dilative volumetric strain.

Determining the minimum and maximum density of sands is critical to accurate estimation of relative density—a key parameter in comparison of laboratory and field test data. Current ASTM methods (ASTM D4253) recommend the use of a vibratory table for maximum density determination. However, studies have shown that different specimen reconstitution techniques can lead to maximum density values that are above the value determined using the ASTM vibratory table method. This discrepancy can lead to an overestimation in the calculated relative density of reconstituted specimens. To further investigate, a sand rainer system composed of a nozzle and a series of stacked sieves was developed with the capability of achieving a wider range of densities. Preliminary results using the sand rainer system showed that densities in excess of the ASTM vibratory method were possible. This study further investigates this exceedance by examining the impact of particle morphology (i.e. angularity) and particle size on the achievable maximum density. Four different uniform sands were tested, including two angular and two rounded at coarse and fine particle sizes. Particle roundness and sphericity values were computed using digital images and computational methods. Minimum and maximum densities for each sand were evaluated using the ASTM method and the custom-built sand rainer system. Results show the importance of particle morphology and size on the maximum achievable density for the two different methods.

Triaxial tests are often used to determine the effective stress strength envelope of soils. Although the linear Mohr-Coulomb envelope is often used in geotechnical engineering, the failure envelope can also be non-linear, with or without a shear stress intercept (i.e., cohesion). Selection of an appropriate mathematical form for the strength envelope is an important step in the interpretation of test data and characterization of soil properties. Thirty-three triaxial data sets were analyzed using a spreadsheet that determines best-fit envelopes for linear, two and three parameter power functions, secant ϕ', and modified Hoek Brown mathematical forms along with the coefficient of variation of the shear strength data. The trends in the type of envelope and variability are discussed. Variability in test data leads to uncertainty in the characterization of shear strength. Possible sources of such variability are the composition of the soil itself and error introduced during testing. The impact of the number of tests and variability on the linear model parameters is assessed for remolded clay and compacted clay. An increase in the number of tests reduces the uncertainty of linear model parameter values but has little effect on the predicted shear strength at a representative normal stress of one atmosphere.

The performance of geotechnical structures founded on normally consolidated (NC) clays under static or dynamic loading is dependent on the soil's strain-softening tendency and the potential for localizations to develop. Prior studies of the localization phenomenon have demonstrated that the addition of viscous (or strain-rate dependent) shearing resistance suppresses the onset of localization and provides a measure of regularization for the numerical simulation of the localization process. The onset of localization is delayed when the reduction in strength due to strain softening is counteracted by the increase in strength due to the increased strain rate that develops within a potential localization zone. Understanding localization tendencies is further complicated by spatial variability in clay properties. This paper presents a numerical study that investigates the combined effects of strain-rate, sensitivity, rate of strain softening, and varying strength profiles on the localization tendencies and the global stress-strain behavior of NC clays. The analyses were performed using the finite difference program FLAC 8.0 with the user-defined constitutive model PM4Silt modified to incorporate strain-rate effects. Parametric analyses examine the influence of strain rate, strength profile variations, local soil brittleness, and mesh size on the global post-peak stress-strain behavior of clays.

Stormwater control measures (SCMs) are increasingly being used instead of traditional, or grey, infrastructure, to control stormwater runoff and mitigate floods in urbanized areas. Vegetated basins are one type of SCM that uses a depression to control runoff volume and enhance water quality. Infiltration basins are the most common type of Vegetated basins and have substantial vegetation and low depression storage with temporary ponding and high infiltration rates. Wet pond/retention basins or wet ponds are another type with large depression storage with permanent ponding, low infiltration rates, little vegetation, and high evaporation. Dry extended detention basins or dry ponds have high depression storage with temporary ponding, low infiltration rates, and less vegetation. Unfortunately, many contractors are not familiar with best practices for constructing infiltration features and compaction can occur inadvertently during construction. This compaction may transform a basin from one type to another or to a new SCM. To identify the influence of soil compaction on this transition, the infiltration performance of a basin located at the headwaters of the Pennypack Creek in Pennsylvania was monitored and the Storm Water Management Model (SWMM) was used to model the basin.

This paper studies the influence of considering small strain behavior on the computation of ground deformations arising from subsurface cavities in sinkhole-prone areas. Sinkholes occur frequently in karst terrain and cause human casualties and major infrastructure damage in karst environments. The testing bed of this study is the analysis of geotechnical failure mechanisms associated with the Winter Park sinkhole; known as Florida’s most devastating sinkhole and one of the largest documented sinkholes in the United States. In this paper, hypoplasticity models for sands and clays are used to model the behavior of silty sands and overconsolidated clays that represent the predominant subsurface soils encountered at the site. Field measurements and published correlations are used for the determination of constitutive soil parameters used in the numerical simulations. PLAXIS 2D is the finite element platform used to capture the geotechnical mechanisms of sinkhole failure. Ground deformations, shear, and volumetric strains arising from the expansion of an underground deep cavity are computed considering the intergranular strain concept in the numerical simulations and are compared against the results obtained using basic hypoplasticity models, which ignores the small strain behavior of soils. It is concluded that by including the small strain soil behavior via the intergranular strain concept, a more realistic representation of sinkhole-induced geotechnical response is provided in terms of maximum ground surface settlements, distortions, and sinkhole influence zones than the corresponding simulations conducted using basic hypoplasticity models.

The New Jersey Meadowlands is roughly 20,500 acres of wetlands, uplands, and developed areas located in the Hudson, Essex, and Bergen Counties of New Jersey, about three miles to the west of New York City. The subsurface profile of the Meadowlands comprises a tidal marsh deposit of thickness ranging from 2 to 33 feet at various locations, which mostly consists of very soft peat and organic clayey silt. The tidal marsh deposit is underlain by soft to firm varved deposits of silts and clays with a thickness of about 100 feet in many locations. Since, both the tidal marsh and the varved silt and clay deposits are highly compressible, designing foundations in the Meadowlands area can be very challenging due to concerns of excessive consolidation settlements. The results of consolidation tests on undisturbed soil samples collected from a total of 17 sites throughout the Meadowlands are compiled and presented in this study. The consolidation tests were performed on 11 samples from the tidal marsh deposit and 65 samples from the varved silt and clay deposit, as part of various projects over the last six decades by AECOM USA, Inc. and its legacy companies—URS Corporation, and Woodward-Clyde-Sherard and Associates. Based on the primary and secondary consolidation parameters, consolidation settlements for a typical range of shallow foundation sizes and contact pressures are estimated using the computer program Settle3D. The bands of settlement curves presented in this paper will provide preliminary estimates of consolidation settlement and thereby assist geotechnical engineers to evaluate the feasibility of shallow foundations for structures, such as buildings, flood walls, levees, etc. in the New Jersey Meadowlands.

This paper investigates the mechanics of torpedo-anchors’ soil interactions in a transparent synthetic surrogate for marine clay, during both embedment and extraction. Both free falling and quasi-statically advanced torpedo anchors were included to cover a range of rates spanning three orders of magnitude (V/D of 0.2-200 s^-1, where V is penetration velocity, and D is torpedo diameter). Impact velocities in the range of 5.0 m/s were investigated. Digital image correlation (DIC) was employed to analyze images of penetration and pullout, captured at a framerate that permitted quantifying incremental displacements. Penetration resistance was found to depend on nose shape. Two nose shapes were studied, and hemispherical noses engendered larger resistance than conical ones; however, shaft resistance is higher behind conical noses, so the combined effect on penetration of a full torpedo is minimal. Resistance in quasi-static pull out tests was the same as in quasi-static penetration tests.

This paper explains the thermally induced volume changes in saturated normally consolidated clays using microscale changes. To achieve this goal, a discrete element model accounting for the physico-chemical interactions between clay particles (i.e., van der Waals attractive and double layer repulsive forces) was employed in this study. The developed model was first validated against thermo-mechanical experimental results then it was used to assess the thermally induced microstructural changes. The evolution of the physico-chemical interparticle forces and the interparticle separation distances showed a thermoplastic response. Such response justifies the thermoplastic contractive strains typically observed in normally consolidated clays.

A discrete element model developed for cohesive soils is utilized to simulate the behavior of saturated clays subjected to drained shearing. The platy-shaped clay particles are modelled, and the physico-chemical forces exist in cohesive assemblies are considered. The numerical specimen preparation mimics the physical clay specimen preparation prior shearing, where a kaolin slurry was one-dimensionally consolidated to a target 1D effective stress, then isotopically-consolidated at 20°C in a temperature-controlled triaxial cell to a target isotropic effective stress. The physical clay specimen was sheared at a constant mean effective stress (drained shearing), and the results were used to validate the numerical model. Simulations of the drained shear strength of saturated clays at a different isotropic effective stress are performed and shown to reproduce the expected drained shearing behavior of clays. Finally, effect of the particle size distribution on the DEM simulation results is also presented and discussed.

This paper presents the results of an experiential investigation to study the influence of plastic and silty fines on the shear strength and porewater pressure (PWP) generation in Ottawa Sands. In order to have a better understanding of the generation and dissipation of PWP during undrained shearing, a novel PWP measurement system was designed to measure PWP at the center of a triaxial specimen. The percentage of plastic and non-plastic fines within the specimens was varied and the specimens were sheared in an undrained triaxial compression test at a constant small strain rate. Factors influencing the strength and the development of PWP (at center and end of specimens) such as relative density, skeletal void ratio, and the fines content along with their plasticity index were investigated.

The oedometer test, which represents the in situ stress conditions (typically called k₀ conditions), is one of the most important geotechnical engineering laboratory tests. For any geotechnical engineering application, k₀ is often used to calculate the lateral stress of the at-rest stress state. Most of the existing analytical expressions for k₀ suffer one or more of the following limitations: (1) they have unrealistic assumptions; (2) k₀ was derived as a constant value for the very high stress state, but implicitly applied to the whole stress range; (3) k₀ equation is often implicit and complicated. In this paper, a new method is used for the data analysis and prediction of k₀ value, which overcomes all of these limitations and was derived upon the definition of k₀ condition without any additional assumption. In addition, the expression can be adopted for any critical state constitutive model for saturated soils. The modified Cam clay model was used to demonstrate the application of the proposed expression. Using this new method, the lateral stresses can be calculated for the oedometer test, and therefore, the stress paths are predicted and compared with the available methods. For verification purposes, the lateral strain increments are predicted and compared to zero. Finally, to check the accuracy of the new method, the predicted void ratio using the new method are compared to the experimental results in the $v-\log {\sigma }_v\text{'}$ plane. A good agreement is reached between the measured and predicted specific volumes. Calculations indicated that a coefficient of determination greater than 99% is reached between the measured and predicted void ratios.

Residual shear strength is considered as a minimum drained shear strength of a soil mass and is used for several geotechnical applications such as designing countermeasures for reactivated landslides, and geotechnical analysis of soils that are prone to progressive failures. Residual shear strength of soils depends on several factors such as mineralogical composition, pore water chemistry, and mode and rate of shearing. In this study, the effect of shearing rate on residual shear strength of soils for soils having two different mineralogical compositions and mixed with pore fluid of two different chemistries, one with distilled water and another with saline pore fluid, was systematically evaluated. The residual shear strengths of the soil were measured with a ring shear device. Each sample was sheared at effective normal stresses ranging from 25 kPa to 800 kPa and shearing rates ranging from 0.001 mm/min to 1 mm/min. The test results showed that the magnitude of residual shear strength variation for soils sheared at different shearing rates depends on the type of clay mineral and pore fluid chemistry. For soils dominated by montmorillonite mineral, there was an average reduction of 12% residual shear strength with an increase in shearing rate by one log cycle, whereas for soils dominated by kaolinite mineral had an average of 25% reduction in shear strength with an increase in shearing rate by one log cycle. Saline pore fluid caused a reduction in liquid limit and eventually an increase in the rate of reduction in residual shear strength with an increase in shearing rate.

Gap-graded cohesionless soils, comprising mixtures of fine and coarse grains, pose a particular challenge in soil mechanics. Reasoning and experimental data indicate that some of the finer grains may exist in the void space without transmitting any stress. A number of authors have proposed considering at least some of the volume of these particles along with the void space when calculating the void ratio in the case of low fines contents. The concept of a transitional fines content has been proposed, i.e., a fines content delineating materials whose behavior is dominated by the coarser grains and materials whose behavior is determined by the finer grains. This contribution uses discrete element method (DEM) simulations to explore the nature of stress transmission in gap-graded materials comprised of spherical particles. Partitioning the stress tensor by considering the contributions of the contacts between coarse particles, the contacts between coarse and fine particles, and the contacts between fine particles is shown to provide useful insight into the contribution of each type of particle to the overall stress transmission. In general, for the mixtures considered here, the coarse-coarse contacts transmit a greater range of forces and a greater average force. For the mixture with size ratio of 3.7, the range of contact force magnitudes transmitted by each contact type reduces with increasing fines content and increasing sample density. This sensitivity is more evident for the lower fines contents studied.

The reliance on sand-based methods for the characterization and design of gravelly soils is necessitated in part by a limited understanding of how to account for the effects of particle size and distribution. In this paper, particle size effects on the strength and fabric of cohesionless, granular media are investigated using the discrete element method by testing specimens with particle size distributions (PSDs) of differing coefficient of uniformity (C_U) and mean grain size (d₅₀). Preliminary results show that when all particle shape characteristics are equal, increasing d₅₀ yields equivalent stress-strain responses for the same relative density (D_R) and C_U. However, when increasing C_U, specimens exhibit more dilative tendencies and greater shear strengths. Increasing C_U results in more dispersive distributions of contact force, stress, and coordination number. The void ratios associated with minimum and maximum density, and constant volume conditions during shear also decrease with increasing C_U.

In this paper, an X-ray computed tomography (CT) imaging-based and machine learning-enabled framework is presented to characterize multi-constituent granular materials. In this framework, X-ray CT is first utilized to obtain raw CT images of a synthetic multi-constituent granular material. Then, a machine learning tool termed trainable Weka segmentation (TWS) is implemented to segment raw X-ray CT images, i.e., to classify constituents and to segregate particles in contact. This is a fundamentally different approach for image segmentation in that it predicts segmentation results based on a trained classifier model that implicitly includes multiple image features and regression functions. Subsequently, segmented images are used to quantitatively analyze microscale information of the granular material such as particle morphology, volume fractions, and spatial distribution of different constituents. The information obtained can be used in microstructure reconstruction and in developing microstructure-informed numerical models. The proposed method has promising potential to handle more complex features in CT images of natural or engineered multi-constituent granular materials.

The development of mechanistic-empirical pavement design has increased demand for measuring performance-related soil properties during earthwork construction. Tools such as the light weight deflectometer (LWD) allow for quantification of the stiffness of subgrade materials during construction. However, a major limitation of the LWD is its inability to provide subgrade stiffness information over the entire project site. The development of continuous compaction control (CCC) has provided the ability to collect near continuous measurements of compaction effort information during the compaction process through the instrumentation of compaction rollers. In this study, LWD and CCC measurements (compactometer value, CMV) were collected during active construction of a roadway. Target modulus values from LWD measurements were determined utilizing AASHTO TP 123-17 to indicate passing and failing LWD tests collected in the field. This study examined general trends between recorded localized CMV measurements and local passing and failing LWD measurements, to assess the utility of CMV as a quality assurance tool for earthwork construction.

The consolidation behavior of dredged material is best determined using a one-dimensional finite strain consolidation theory which requires a full variation void ratio at low and high effective stress levels. The United States Army Corps of Engineers (USACE) suggests using a self-weight consolidation test apparatus comprised of eighteen 6-inch diameter removable rings to obtain a void ratio and effective stress relationship for very low effective stresses. In this study, a simplified laboratory testing apparatus of a self-weight consolidation test has been developed and used to investigate the consolidation behavior of dredged material obtained from the Savannah River. The results suggest that the proposed self-weight consolidation apparatus can be used to obtain a reliable relationship between void ratio and effective stress for materials with high initial void ratios.

Many offshore energy production and recovery structures such as wind turbines, offshore tidal turbines, and oil/gas platforms are built on carbonate sands, which predominantly consist of the skeletal remains of marine organisms. Particles of carbonate sands have highly porous grain structures with intra-granular voids. Such porous grain structure results in a much more compressible soil grain than terrigenous (i.e., quartz-based) sands, which have solid grain structure. As a result, calcareous sands exhibit engineering and mechanical characteristics that are different than that of quartzitic sands. While there is a significant amount of experience on the performance of foundation systems on terrigenous sediments, expanding offshore infrastructure construction on carbonate sands brings considerable challenges. This study focuses on micro-scale characterization of carbonate sands as a first step to overcome this challenge. For this purpose, nanoindentation tests were performed on ten different carbonate sand samples. Mechanical properties of carbonate sand grains were determined using nanoindentation techniques. A series of peak loads are applied by the nanoindenter on the grain surface and load-displacement curves are developed to estimate Young’s modulus and hardness values of the carbonate sand grains. Modulus and hardness of the carbonate sand grains were considerably lower than those reported for quartzitic sand grains. Test results cumulatively show that modulus and hardness values of carbonate sands are highly dependent on indentation depth. Considerable softening with increasing indentation depth was observed; both the modulus and hardness values of carbonate sand grains show a significant decrease at larger indentation depths. Furthermore, high inter-sample and inter-grain variation of mechanical properties was observed. This study on the micro-scale characterization of carbonate sands provides insight on their distinctive macro-scale behavior.

Selection of shear strength parameters for geotechnical analyses is often informed by laboratory testing of compacted and undisturbed soil samples. Laboratory tests commonly used to characterize peak shear strength include direct shear tests, direct simple shear tests, and triaxial compression tests. Consolidated-undrained triaxial compression tests with pore-pressure measurements are particularly useful and common, because the test results allow for interpretation of both drained and undrained strength parameters. Even though stress conditions in the field are generally anisotropic, samples for consolidated-undrained triaxial compression tests are most often isotropically consolidated. For cases where strength interpretation requires that the in situ stress conditions be considered, empirical and theoretical correlations between undrained shear strength from these differing consolidation-stress conditions are available to understand the potential differences in shear strength parameters. This paper presents an overview of previously proposed empirical and theoretical correlations. The methods are evaluated using a shear strength database of soils for which both isotropically and anisotropically consolidated-undrained triaxial compression tests were performed. Based on a review of the predicted and measured shear strengths, practical recommendations are made for use in engineering practice.

There exists a number of semi-empirical relationships assessing void ratio in the literature. The predictive performances of widely used void ratio relationships are assessed within a probabilistic framework with the use of compiled database. The database, which consists of 636 non-plastic silts, sands, and gravels is compiled from the existing literature having minimum, maximum void ratio, mean grain size, coefficient of uniformity, particle roundness and sphericity, fines content parameters. Among predictive models, which use D₅₀ as an input parameter, Chen and Kulhawy model produced the least error (μ_error=-0.006, σ_error=0.125) and is concluded to be more accurate compared to Cubrinovski and Ishihara model (μ_error=-0.055, σ_error=0.140). Similarly, Zheng and Hycriw, which uses C_u as an input parameter produced more accurate predictions (μ_error=-0.034, σ_error=0.069), when compared to Chen and Kulhawy model (μ_error=-0.062, σ_error=0.137).

While most municipal solid waste (MSW) landfills maintain temperatures below 55°C (131°F), relatively few MSW landfills have temperatures exceeding 93°C (200°F). In order to understand the key mechanisms that allow heat accumulation and temperature rise, commercial geothermal model TETRAD was used to simulate the heat transfer in an MSW landfill located in the northeastern United States. Field temperatures of the landfill have been monitored using fiber optics sensors. Waste heat generation and vertical leachate flow were the key variables evaluated in the modeling. The model results indicated that the average initial waste heat generation rates for this landfill ranged from 0.7 to 0.8 W/m³ reflective of relatively young waste and they were about 0.2 W/m³ for maintaining steady-state temperature conditions in the landfill. The rate of heat generation reduced as the waste aged and the vertically downward flow of leachate removed heat and reduced the peak temperature.

Understanding the role of normal stress variations in rock joints with fill materials has important implications for interpretation of rock slope failures, fault movements, and earthquake nucleation. In this study, the main objective is to explore the impact of normal stress variations on shear failure of granular fill materials by utilizing ultrasonic shear waves. For this purpose, granular quartz specimens were sheared in a single direct shear apparatus equipped with an ultrasonic imaging system. The experimental program consisted of different phases to simulate natural conditions including the reduction in the applied effective stress. The obtained data provided measures of variations in shear strength and frictional stability as well as ultrasonic wave attributes with the changes in normal stress and shearing velocity. The results indicated a close link between the changes in ultrasonic amplitude and the layer porosity. Observed slip and creep phases were also captured in the transmitted amplitude variations. Moreover, an ultrasonic precursor to the dynamic shear failure was identified in the form the transmitted amplitude rate change.

The use of stress waves for geophysical and non-destructive testing (NDT) applications continues to grow within the geotechnical community. For example, the quality control and assurance (QC/QA) process for deep foundations often relies on NDT methods such as cross-hole sonic logging (CSL), cross-hole sonic tomography (CST), and parallel seismic (PS) that are based on the propagation of stress waves through the foundation. Although these methods are the standard techniques in the deep foundation industry, they are known to have limitations in detecting defects. Therefore, it becomes important to effectively and efficiently model the propagation of stress waves in order to advance the state of practice with respect to deep foundation NDT. For example, full waveform inversion (FWI) of stress waves is a novel technique that has shown promising performance in providing high resolution images for geophysical/NDT applications at multiple scales of interest. Unlike methods that solely rely on the first time of the arrival of the stress waves, FWI attempts to match entire recorded waveforms. Hence, it requires an accurate simulation of wave propagation through the domain. Moreover, FWI is a computationally expensive approach as it requires multiple iterations to solve the inverse problem. The spectral element method (SEM) offers an efficient solution to the forward problem of wave propagation in terms of both accuracy and computational time. This study first provides a brief overview of the spectral element method. Then the application of SEM in non-destructive testing for quality control and assurance of drilled shafts is presented through a series of numerical simulations that model stress wave propagation for FWI and compare it to a finite-difference method (FDM) approach.

Evapotranspiration (ET) cover system is an alternative practice for landfill closure compared to the conventional approach because of its durability and low cost of construction. The performance of ET covers largely depends on the soil water storage (SWS) capacity of the cover soil. The variation of soil moisture due to the fluctuation of the environmental conditions such as precipitation and temperature significantly affects the SWS capacity which is one of the key water balance components of ET cover systems. Therefore, a continuous monitoring and estimation of SWS of ET covers are essential for their performance evaluation. The SWS of ET covers is typically assessed through installed moisture sensors in the cover soil. However, the installation of sensors in the field can be expensive and time-consuming. Furthermore, in most of cases, typical sensors are unsuitable for long-term monitoring of moisture content of soil and thereby the SWS. Hence, the objective of this study was to evaluate the SWS of test section ET cover using an alternative non-destructive geophysical method. In this study, electrical resistivity imaging (ERI) was employed. Monthly field testing was performed on instrumented drainage lysimeters (12 m×12 m×1.2 m) constructed at the City of Denton Landfill, Texas. The lysimeters were constructed with fine-grained soil (CH). SWS was determined through integrating the point measurement of moisture content collected from the installed moisture and temperature sensors over the entire soil depth. The ERI method was performed in the field across the locations of the sensors. Resistivity values at the equivalent depths of the sensors were logged from the field test and integrated throughout the cover depth to determine unit cross-sectional area resistance (ρ_a). Based on the data analysis, an inverse relationship was observed between the SWS and ρ_a. The ρ_a values ranged between approximately 7 to 42 Ω-m², which corresponded to a wide range of SWS in the field. Based on the results, the ERI method was found to be an effective tool to monitor SWS of ET cover system.

Seismic sensors can be used for a wide variety of applications, including vibration monitoring, near-surface imaging, and horizontal to vertical spectral ratio (HVSR) techniques (e.g. sediment layering and seismic zoning). Unfortunately, professionally developed and engineered seismic sensors are typically expensive, which can make them inaccessible to engineers and researchers without financial resources, such as those in developing countries. As an alternative to these professional, but expensive instruments, we have developed a seismic sensor using a microcontroller that is much more affordable and can perform many of the same applications as the more traditional, professional systems. Our system uses a microcontroller paired with a 24-bit analog to digital converter (ADC) to record seismic signals from three orthogonal axes with an effective resolution of 5 μV and sampling rates up to 250 Hz. In addition, a GPS module is used to record the location (GPS coordinates) of the sensor and to correlate the recorded signals with real time so that signals collected by individual sensors may be meaningfully combined to create sensor arrays.

Discrete element method (DEM) has been widely applied to simulate granular soil behavior. However, traditional DEM uses sphere clusters to approximate realistic particles, which is computationally demanding when simulating many particles. This study explores the use of physics engine, a platform developed for simulating physical processes in video games, to simulate realistic particles. This paper compares realistic particle simulation methodologies using physics engine and discrete element method, including contact models, parameter settings, computational speeds, and simulation results. The results show that the physics engine and DEM achieve similar simulation outputs, while the physics engine runs significantly faster than DEM, because PhysX uses both CPUs (central processing units) and GPUs (graphics processing units) of computers, triangular face tessellations to represent realistic particles, and a simplified contact model to accelerate simulations. This study provides geo-mechanicians and DEM modelers with one more option for them to consider when they simulate realistic particles.

Granular materials like sandy and gravely soils are composed of an assembly of individual particles. A given soil deposit or specimen has a specific arrangement of individual particles, clumps of particles, and void spaces, which along with the orientation of inter-particle contacts, encompasses the basis of the soil fabric concept. Experimentally soil, fabric can be quantified by non-destructive methods such as image microscopy and X-ray computed tomography. While these state-of-the-art methods provide accurate and useful information, they require specialized equipment and analysis methods. This has ushered a rapid increase in the use of particle-based numerical tools, such as the discrete element method (DEM), which enable the study of behaviors at the micromechanical- and element-scales. In this paper, we investigate the behavior of specimens in oedometric (1D) and isotropic compression using 2D DEM simulations. To quantify the fabric of the specimens in DEM, scalar descriptors (void ratio, coordination number, and number of rattlers) and vector fabric descriptors (contact normal direction, contact normal forces, and shear forces) were monitored at different stages of oedometric and isotropic compression. The results presented herein provide a comparison of the trends captured by the different fabric descriptors and highlight the effect of fabric anisotropy on the macroscopic response.

Internal erosion is a potential failure mode of earth dams and levees and consists of the mobilization of solid grains as water flows through granular material. This paper focuses on the study of the suffusion mechanism in internally unstable soils. Typically these soils are broadly graded in nature, in which a finer fraction is subjected to erosion and is transported through the voids in the matrix of coarser particles. The material point method (MPM) has shown promise in large deformation modeling of geotechnical problems. Here, an extension of the two-phase double-point MPM formulation is proposed to model the suffusion internal erosion mechanism. MPM is a particle-based method defined in a continuum framework, and the two-phase double-point approach uses two separate sets of material points to represent the liquid and solid phases. Transferring mass between the two layers of material points has applications in fines migration in internal erosion, selective transport in sediment transport, and dissolution of solids. The numerical results demonstrate the capability of the formulation to transfer mass between solid and liquid phases while ensuring that the total mass is automatically conserved.

Traditionally, geotechnical engineers have used continuum numerical methods coupled with complex constitutive models to analyze soil response. This approach, however, does not explicitly consider the particle-scale interactions underlying the macro-scale behavior. Given the advances in computational power, particle-based discrete element methods have been progressively catching the attention of geotechnical engineers in simulating and analyzing soil behavior. For validation of discrete element modeling of various laboratory tests, many researchers have been using idealized granular materials such as steel spheres that are much simpler to model compared to real soils. In case of experimental validation of models for simple shear test using stacked-ring device type, it is particularly important to ensure that the simple shear condition is completely imposed on specimens consisting of low friction and freely rotating steel spheres. In this study, discrete element modeling is used to examine the level of simple shear imposition on specimen of uniform-sized steel spheres in large scale stacked-ring simple shear device under constant volume conditions.

In this study, the stability of jointed rock slope was evaluated using the finite element method (FEM) with the random-joints generation 2D model. The in-house model to simulate joints randomly generated in the rock was developed based on the Monte Carlo method and a normal probability distribution that can be obtained in the field investigation. The model was employed into COMSOL Multiphysics through a subroutine program written by MATLAB. As for the mechanical parameters of joints, the S-type weakening curve equation was used so that each joint has individual mechanical parameters. Compared to a conventional model to simulate the joints, the developed model can simulate the physical characteristics of the jointed rock slope, which reflects the control function of joints in the stability of the rock slope closed to the field. To validate the model, the failure case of jointed rock slope in the field was compared to one predicted by this random joint model. The results were in good agreement with deformation characteristics of the slope observed in the field.

Computational design optimization is a developing discipline in engineering that has the potential to lead to significantly more efficient designs with concomitant economic and environmental benefits. The approach is currently finding application in areas such as mechanical component design and the structural design of trusses. This paper describes recent work applying an integrated optimization approach to the ultimate limit state design of geotechnical structures. The approach described is built on the discontinuity layout optimization (DLO) method that utilizes optimization and limit analysis to directly determine the critical collapse mechanism for any soil geometry and loading configuration. However, by changing the objective of the optimization, the method can be made to automatically identify an optimal design, rather than the critical collapse mechanism. The approach is illustrated through several examples, including a reinforced soil slope and a wind turbine foundation system.

Considering heterogeneous media for foundation of dams in modeling of infrastructure such as dam-reservoir-foundation coupled system leads to considerable increase in time and costs of analysis. On the other hand, simplifying the problem by assuming homogeneity, which is a common approach among research owing to complexity of this natural media, increases the level of uncertainty. The purpose of this paper is to evaluate the effect of uncertainties in mechanical properties of foundations on the seismic response of concrete gravity dam-reservoir-foundation system. Toward this end, Pine Flat Dam is used as a reference case and three levels of earthquake intensities of operation basis earthquake (OBE), maximum design earthquake (MDE), and maximum credible earthquake (MCE) are imposed to each model. Deconvolution process is then carried out to elaborate the significance of this approach. It is demonstrated that neglecting deconvolution process will lead to underestimating the exceedance probability (EP) curves, especially at the higher levels of intensity for the input motions. In addition, it is shown that by increasing the intensity of earthquake, EP curves are shifting up in a way that the probability of undergoing severe damage in MCE level is more than 90% while this probability for OBE level is less than 5%.

The goal of this paper is to numerically assess the impact of biopolymer-based pore fluid on soil behavior. The use of biopolymer-based pore fluids is increasing nowadays due to advancements in biogeotechnology methods. These advancements, however, rely on trial and error identifying the most suitable biopolymer and its concentration to avoid strength losses in the soil. Furthermore, the use of clay fillers to stabilize biopolymers preserving the overall strength of the soil is performed arbitrarily without scientific basis. In this study, the response of biopolymer-based pore fluid is modeled using coarse-grained molecular dynamics and compared to the response of conventional pore water. The impact of different percentages of clay filler is also investigated. The results of this study show that the viscosity of filler-stabilized biopolymers at low shearing speeds is significantly higher than that of traditional pore water. However, the viscosity of these biopolymers drops significantly reaching to the water viscosity as the shearing speed (i.e., rate) increases. Such response was observed for all clay filler percentages with an increase in the viscosity as the filler percentage increases. Furthermore, using a less concentrated biopolymer in the pore fluid showed a significant reduction in the viscosity. These results will allow better design and selection of the biopolymer-based pore fluids for various biogeotechnology applications.

A recent study of over 40 organic clay sites subjected to piezocone penetration tests (CPTu) found that the conventional soil behavioral type charts did not identify these materials properly (specifically zone 2), but instead were mostly categorized as either zone 3 (clays) or zone 4 (silts). An alternate CPTu methodology is presented for a more reliable approach to detecting organic clays and peats which mainly requires three parameters: net cone resistance, effective cone resistance, and excess porewater pressures. Once properly identified, a simple expression is used to assess the profile of effective preconsolidation stress in these organic geomaterials in terms of the net cone tip resistance in a power law format.

The detection of deleterious materials in compacted soil fills is an important part of earthwork construction. These materials are often identified a priori using laboratory techniques such as the visual assessment of sieve analyses. However, it is possible that deleterious materials, such as clay pockets, can be larger than particles characterized in laboratory tests. Bench scale imaging using simulated unmanned aerial vehicle flights were conducted to determine if clay pockets, 15.24 cm by 15.24 cm by 5 cm thick, could be detected in granular soils. The imaging techniques employed were digital imaging, thermal imaging, and electromagnetic imaging. All imaging techniques could be used to identify clay pockets at the surface, but only electromagnetic imaging could detect clay pockets beneath the surface. The clay pockets were easily identifiable at depths of 2.5 cm and 15.2 cm in fine sand. When buried in pea gravel, the clay pockets were identifiable only at a depth of 2.5 cm. The clay pockets could not be identified when buried in gravel sized particles.

Estimated geotechnical properties are unavoidably affected by various uncertainties. Quantifying the uncertainty in estimated geotechnical properties relies on probabilistic models adopted in the data analysis. Gaussian random field model (RFM) is one of the most prevailing models used in conventional geotechnical data analysis. A recent perceptible trend is to make uses of machine learning (ML) algorithms (including supervised and unsupervised algorithms, etc.) to quantify the uncertainty in geotechnical properties using site investigation data. However, ML algorithms often adopt probabilistic models (e.g., linear dynamic system, LDS) different from conventional ones (e.g., Gaussian RFM) that geotechnical practitioners are familiar with. Effects of using conventional probabilistic models and those adopted in ML algorithms (e.g., Gaussian RFM vs. LDS) on geotechnical uncertainty quantification remain unexplored and unknown. This paper presents a comparative study on uncertainty quantification of soil total unit weight γ using cone penetration test (CPT) data based on Gaussian RFM and LDS. These two models are combined with an empirical correlation relating γ to CPT data to quantify the uncertainty in the profile of γ over the depth. Their effects are illustrated and discussed based on a set of real CPT data.

The fines content (FC) of a soil is needed in order to assess its susceptibility to liquefaction in earthquake engineering, as well as for evaluating its overall soil behavior. In the absence of soil sampling and laboratory testing, reliable in situ testing correlations offer a practical alternative. The cone penetration test (CPT) has been used to estimate FC through trends established with the soil behavior type index (I_c) and this paper presents a summary of published algorithms for this purpose. Several of these appear to give estimated FC with high uncertainty and/or results that are site-dependent. A large laboratory FC-CPT database is compiled from 53 well-documented test sites located in different countries. A global FC-CPT correlation is developed, and a new formulation is derived to improve current FC estimates using a modified CPT material index, I_B.

Laterally-loaded short rigid drilled shaft foundations are the primary foundation used within the electric power transmission line industry to support steel monopole structures. Performance of these foundations is highly dependent on modulus of the subsurface that is best measured by the pressuremeter test. The pressuremeter test, however, is expensive to conduct and rarely performed. Correlations of pressuremeter modulus to blow counts and other index properties have been developed. But these correlations have high variability and may result in unconservative foundation design. Variability in correlations is due, in part, because of the differences in the direction of loading of the correlated properties and the direction of loading during pressuremeter testing. The shear wave velocity, measured using the surrogate surface wave velocity through refraction microtremor methods, can be used to measure small strain, shear modulus in the lateral direction. In theory, the intermediate strain modulus of the pressuremeter test is proportional to the small strain modulus derived from shear wave velocity. A correlation between intermediate and small strain moduli is developed here, based on geophysical surveys conducted at fourteen previous pressuremeter test locations throughout the Sonoran Desert of central Arizona.

The Minnesota Department of Transportation (MnDOT) studied a variety of stormwater storage facility (SSF) concepts to mitigate flooding events along Interstate 35W (I-35W) in Minneapolis near 42^nd Street South. After evaluation of these concepts a deep storage structure with lift station concept located on the shoulder of I-35W northbound between 42^nd Street South and 40^th Street South was selected. The project area is located near the edge of a glacial erosional channel between glacial deposits and bedrock. The investigation informs the understanding the geology and geotechnical aspects of the site and supports a geotechnical data report (GDR) and a geotechnical interpretive report (GIR). The investigation included a variety of methods including geophysical multichannel analysis of surface waves (MASW); standard penetration test geotechnical borings; in situ instrumentation with vibrating wire piezometer nests; multiple rotosonic borings; and a pump test. The paper presents an overview of the investigation and findings and how these results informed preparation of the GDR and GIR documents.

The electric cone penetrometer test (CPT) is becoming a popular subsurface investigation tool to understand a site’s soil stratigraphy and to estimate geotechnical design parameters. Moreover, CPTs are also a valuable tool to identify potential subsurface geohazards, such as potential liquefiable sand layers or subsurface karst anomalies indicative to sinkhole collapse. In this study, the authors review the current methodologies to detect and characterize subsurface karst soil anomalies and implement statistical regression procedures to set critical values of the sinkhole raveling index (RI). This was performed through analysis of 150 CPT soundings performed in Central Florida at sinkhole active sites. The RI value was calculated for each CPT, and the classification of CPT was categorized into severities of sinkhole formation based on its proximity to the reported sinkhole incident. Probability functions were then developed for the datasets, in turn relating RI data to the general probability of sinkhole manifestation at the ground surface. The results suggest that an RI value greater than 0.50 corresponds to an approximate range of 58–62% chance of sinkhole manifestation at the ground surface. Although this analysis technique does not incorporate the physical mechanism of internal erosion (i.e., raveling propagation over time), the developed analysis can still be used to better understand the potential of sinkhole formation within a project site when internally eroded soils are detected.

Soil particle size and shape are of great interest to the geotechnical engineering community because they affect soil behavior. Determination of soil type is an important requirement in geotechnical engineering projects such as developing a site-specific soil profile or performing a geotechnical design. Geologic formation of sand usually results in sand particles with distinct visual characteristics such as size, color, and shape. In this study, dynamic image analysis (DIA) is employed to extract particle size and shape descriptors which were then used for the classification of sand. Five different types of siliceous sand with different particle shapes were selected for investigation. A training dataset of grading and shape properties of these sands was compiled from over 50,000 images. This was accomplished using machine learning models based on convolutional neural networks. This method allows for automatic sand/particle classification which may eventually assist engineers on-site to quickly determine geotechnical properties of soil formations that would normally be analyzed in laboratories.

Mapping bedrock layers and their stiffness is an important part of geotechnical site characterization, particularly for highway projects that require significant rock excavation. A variety of invasive and non-invasive techniques can be used for this purpose. In this study, microtremor horizontal to vertical spectra ratio (MHVSR) and multichannel analysis of surface wave (MASW) methods were utilized along a proposed highway alignment, where the bedrock conditions are expected to be very shallow and highly variable. Two/three peaks were observed for the majority of the MHVSR measurements. The origin of the peaks was investigated using the proposed eye shape method in the literature and it was observed that an eye-shape spectral pattern is not always an accurate indicator of a peak with stratigraphic origin. MHVSR peaks in this study were determine to be of stratigraphy origin as they correspond well with the sharp impedance contrasts in the Vs profiles and subsurface layering from the boring logs. It seems that for cases of MHVSR with multiple peaks at very shallow bedrock sites, the peaks are reliable and they typically have a stratigraphy origin. This suggests that the MHVSR technique is a suitable non-destructive, rapid, and cost-effective alternative for traditional drilling and sampling for shallow bedrock mapping.

A variety of soil classification charts have been proposed in the literature to identify soil behavior type (SBT) based on piezocone penetration test (CPTU). In this paper, the performance of four CPTU-based soil classification charts is evaluated using a CPTU and borehole database for offshore sediments in the Pearl River Estuary, China. Statistical analysis is conducted to evaluate the agreement between soil zones in the soil classification charts and soil types by boreholes. The results imply that most soil types interpreted by CPTU data agree well with those determined by borehole data, and a dominating soil type-soil zone relationship can be identified for each soil classification chart. The main challenge is perhaps the overlap of multiple soil types in one soil zone in the soil classification charts, particular for soil mixtures.

The vision cone penetrometer (VisCPT) fits a traditional cone penetrometer (CPT) with a camera to obtain continuous in situ soil images. A previously developed image analysis method determines several textural indices for each captured image. The textural index profiles can identify thin soil layers and lenses that may be undetected by the CPT. A newly redesigned VisCPT having a much higher resolution camera than in previous VisCPTs has been developed. The larger resolution expands the range of soil sizes that can be optically characterized by the system. Updated hardware and image analysis techniques will enhance the capabilities of the VisCPT for generating accurate soil profiles.