Journal of Geotechnical and Geoenvironmental Engineering

The stability of gravity-retaining structures has traditionally been checked within the limit equilibrium framework. However, limit equilibrium methods require that prior assumptions be made regarding the collapse mechanism of the wall–soil system. Using the strength reduction method (SRM) with finite-element analysis (FEA) to analyze the stability of a wall does not require the collapse mechanism of the wall–soil system or even its general form or location to be known a priori; instead, it results from the analysis automatically. This paper uses the results of SRM-based FEA simulations performed using a sophisticated two-surface-plasticity sand model to evaluate the stability and factor of safety of gravity-retaining walls. The SRM-based FEA simulations were performed via ABAQUS and Python scripting using novel strength reduction techniques for both the backfill soil and the gravity wall. The generalized bisection method was used as the search algorithm to find the minimum backfill relative density $D_{R,\min }$ or the minimum wall width $B_{\min }$ just prior to the instability and collapse of the wall–soil system. The stability of the wall–soil system was detected based on the convergence (or lack thereof) of the Newton–Raphson (N-R) iterative solution implemented in an implicit FE modeling scheme. The proposed approach does not rely on the assumption that a wall would independently achieve overturning, sliding, or bearing capacity limit states and is therefore more accurate in describing wall stability.

Numerical investigation of free-standing cantilever walls subjected to horizontal seismic loads was carried out using nonlinear elastoplastic finite-element approach. The numerical model was validated using centrifuge tests and a numerical study. This study emphasizes the acceleration response, deformation mechanism, and active earth thrust ($P_{\mathrm{ae}}$) of seismically induced cantilever retaining walls. A detailed parametric study was conducted to analyze the effect of the entire earthquake motion, wall dimensions, and soil characteristics on the active earth thrust behind the wall stem ($P_{\mathrm{ae}\_\mathrm{stem}}$) and along the virtual plane passing through the wall heel ($P_{\mathrm{ae}\_\mathrm{vp}}$). The study found that the $P_{\mathrm{ae}\_\mathrm{stem}}$ and $P_{\mathrm{ae}\_\mathrm{vp}}$ decrease with an increase in peak ground acceleration (PGA) up to approximately 0.55 g because they are impacted significantly by the translational and rotational displacement of the cantilever wall. In addition, the magnitude of $P_{\mathrm{ae}\_\mathrm{stem}}$ is smaller than that of $P_{\mathrm{ae}\_\mathrm{vp}}$. Based on the parametric investigation and regression analysis, an equation for $P_{\mathrm{ae}\_\mathrm{stem}}$ and $P_{\mathrm{ae}\_\mathrm{vp}}$ is proposed and was verified by comparing it with the results of the finite-element study and existing numerical work. The proposed equation provides improved prediction of the active earth thrust of a cantilever wall at an early design stage.

This paper evaluates the stress changes and settlements following dissipation of local, 3D excess pore pressure fields induced by controlled blasting. Field data gathered during a blasting experiment in medium dense sand deposits at the Port of Portland, Oregon, were used to validate the numerical simulations. The field measurements included cone penetration tests, excess pore pressure ($u_e$), dissipation, and ground surface and subsurface settlements. The proposed numerical framework consisted of a 2D finite-element approach using a critical state–based hypoplasticity constitutive soil model capable of reproducing changes in void ratio, thus capturing soil densification to study soil arching mechanisms as a result of the dissipation of the local $u_e$ field. The soil parameters were calibrated to match laboratory test results performed on reconstituted specimens of medium dense sand and intact specimens of medium stiff silt obtained at the project site. The methodology was validated using the field measurements in terms of changes in tip resistance, shear wave velocities, and distribution of ground surface and subsurface volumetric strains and displacements. The field measurements and numerical results were used to draw conclusions regarding the variability of the postdissipation stress field within the blasted area due to soil arching. The main variables contributing to the development of liquefaction-induced soil arching as a result of controlled blasting were analyzed in a parametric study. The effects of the extent of the blasting zone as a function of the width-to-height ratio ($W/H$) and blasting intensity quantified with the excess pore pressure ratio ($r_u$) were investigated. Results of the parametric study include the identification of significant reductions in mean effective stresses occurring within the blasting zone for small $W/H$ ratios regardless of the input $r_u$. A discussion regarding blast-induced cone tip resistance ($q_t$) changes with time to explain $q_t$ reductions through the lens of case histories and implications for soil arching concludes this study.

Several approaches have been proposed to improve oil-contaminated soil remediation. However, the role of zeolite, a safe, clean, economical, and environmentally friendly material, in removing crude oil (CO) from contaminated soils remains unclear. This paper addresses this gap with respect to CO-contaminated sands (COCS) and aims to assess zeolite’s capability as a geo-environmentally adaptable material to mitigate the adverse impacts of oil pollution on sandy soils. The cyclic simple shear behavior and chemical analysis of coarse and fine-grain silicate sands are investigated and compared in response to CO contamination. Clean sand specimens were prepared with 60% relative density, whereas COCS specimens were prepared using a 6% crude oil contamination level. This study examines the impact of CO contamination and the use of an environmentally friendly stabilizer through simple shear tests (under static and cyclic conditions), consolidation experiments, and Fourier-transform infrared spectroscopy (FTIR). Optimal pollution adsorption was achieved by adding 6% zeolite to fine-grained sand, resulting in a 31.61% increase in the shear modulus index and an 18.70% increase in the friction angle index. Using 8% zeolite improved the shear modulus and friction angle indexes in coarse-grained sand by 21.69% and 11.83%, respectively. FTIR results showed a 45% and 59% enhancement in coarse and fine sands, respectively, indicating the positive role of zeolite in stabilizing COCS through pollutant adsorption. The superior performance of zeolite in fine-grained compared with coarse-grained sand is justified by its higher specific surface area and porous surface.

Load transfer platform (LTP) plays an important role in load transfer between piles and subsoil in pile-supported embankments over soft soils. This study conducted spring-based trapdoor tests to investigate the load transfer mechanisms of LTPs with unreinforced and geosynthetic-reinforced river sand and lightweight aggregate (LWA) subjected to differential movement. Spring-based trapdoor tests were used to simulate the differential movement below the LTP under fill placement and surface footing loading to investigate the mobilization and degradation of soil arching and tensioned membrane effects above the trapdoor (simulating the subsoil settlement). To evaluate the trapdoor rigidity effect, both rigid (one-segment) and flexible (three-segment) trapdoors were utilized. Test results revealed that LWA, when utilized as an LTP material, could effectively improve the mobilization of soil arching, hinder the degradation of soil arching, and reduce the trapdoor settlement. LWA was proven to be a good alternative LTP fill material in pile-supported embankments. Geosynthetic reinforcement was beneficial to minimize degradation of soil arching. In the rigid trapdoor tests, the tensioned membrane effect was progressively mobilized with the applied footing pressure. However, the flexible trapdoor tests showed rapid mobilization of the tensioned membrane effect, followed by a sustained mobilization, and then a rapid arching degradation after a certain applied pressure was reached and continued. Under surface footing loading, the embankment with the LWA as the LTP fill material showed an inverted tower-shape deformation pattern, whereas that with the river sand as the LTP material exhibited a rectangular deformation pattern.

Liquefaction-induced ground failure poses substantial challenges to geotechnical earthquake engineering design. Current approaches for designing against liquefaction hazards, as specified in most seismic provisions, focus on estimating a liquefaction factor of safety ($F{S}_L$) and typically characterize earthquake loading using design parameters based on probabilistic or deterministic ground motion levels. Because $F{S}_L$ is estimated deterministically, this basis of design neglects considerable uncertainties for estimating liquefaction triggering and its consequences and results in a lack of liquefaction-specific design criteria, particularly as structural design has advanced toward risk-targeted performance objectives. This study presents a framework for developing liquefaction-targeted design criteria based on a minimum acceptable return period of liquefaction, informed by probabilistic liquefaction hazard analysis (PLHA). PLHA quantifies annualized rates of liquefaction by considering contributions from (1) the full ground-motion probability space, and (2) uncertainties in liquefaction triggering using probabilistic models. PLHA is used in this study to characterize the current, effective return periods of $F{S}_L$ ($T_{R,FS}$) obtained from conventional liquefaction hazard analysis (CLHA) using uniform-hazard ground motions. $T_{R,FS}$ is evaluated in a parametric study of nearly 100 sites throughout the conterminous United States. The results indicate large geographic variations in acceptable liquefaction hazard levels, with implied $T_{R,FS}$ ranging between approximately 1,000 to 3,000 years. To address these inconsistencies without the computational demands of full PLHA, a framework is proposed for developing a liquefaction-targeted design peak ground acceleration, $PG{A}_L$, for use in liquefaction models that result in consistent liquefaction design levels across all geographic locations. The mapped $PG{A}_L$ is shown to be somewhat sensitive to site-specific properties, and adjustment factors are developed and presented. The proposed $PG{A}_L$ mapping procedure produces $F{S}_L$ estimates that are consistent with those obtained from full PLHA at a target $T_{R,FS}$, providing a promising roadmap to incorporating PLHA concepts into current liquefaction design methods.

Soil suction is a crucial parameter that affects the behavior of unsaturated soils. The impact of temperature on suction can lead to significant changes in the hydromechanical response of unsaturated soils. However, current models that describe the temperature dependency of soil suction rely mainly on empirical and semiempirical relationships, which do not fully consider the contribution of soil structure and degree of saturation on enthalpy potential. To address this limitation, we propose a novel general model for temperature-dependent soil suction based on thermodynamic laws. The model accounts for the thermodynamic processes that determine the enthalpy of the soil and uses these processes to develop the mathematical relationships required for the model. Specifically, we expand the Gibbs free energy for both internal chemical exchanges and when dealing with the thermodynamic system as a whole. We then combine the resulting equations to obtain a general model for the soil total suction. The model is validated by comparing its predictions against laboratory-measured suction at different temperatures for different soils reported in the literature. Furthermore, we demonstrate the model’s potential by showing an application in simulating the soil-water retention curve at different temperatures. The proposed model can contribute to a better understanding of the behavior of unsaturated soils under varying temperature conditions by providing a comprehensive and physics-based approach to modeling temperature-dependent soil suction.

Vacuum preloading via prefabricated horizontal drains (PHDs) is an efficient technique to accelerate the consolidation of dredged soft soils. However, this technique lacks a clear and concise theoretical solution to the PHD vacuum consolidation analysis for slurry. To address this issue, this study proposes a novel analytical solution based on a mathematical logical procedure. The governing equations are first derived based on square PHD consolidation unit cells given the assumption of equal strain, taking into account various drainage conditions at the boundaries and the horizontal and vertical spacings of PHD. A seepage direction coefficient, directly determined through PHD spacing without additional identification, is further introduced into the derived formulation to enhance the solution to be more consistent with the results of free strain consolidation analysis. Then, the proposed analytical solution is validated based on three laboratory and field tests. The proposed solution is successfully applied to estimate the consolidation behavior at a site in Aomori Prefecture, Japan, involving PHD vacuum preloading. All results demonstrate that the proposed analytical solution is applicable for the design and management of PHD vacuum preloading construction projects and practically useful for engineers. Furthermore, the influences of the large strain effect, variable hydraulic conductivity, and variable compressibility on the consolidation analysis are discussed.

Compaction is an essential compression process for sedimentary soils. Compared with in-depth studies on granular soil behaviors, numerical modeling of clay compaction is still in its infancy. This study presents an all-atomic modeling framework to investigate the compaction of anhydrous montmorillonite from initially fully exfoliated platelets. The total number of interparticle contacts increased, and the mesopores were dominant during the formation of card-house structures. As the local fabrics evolved into book-house structures, the contact evolutions became predominant, and partial mesopores transformed into micropores. The coordinated deformations during the formation of compacted aggregates dramatically increased interparticle contacts, and so the micropores became dominant. After rebound, the interparticle contacts decreased and partial micropores were restored. The total potential energy decreased during contact evolutions due to the significant reduction in interaction potential energy between clay particles, while hysteresis was observed during coordinated deformations and rebound due to the changes in internal potential energy within deformed clay particles. The internal potential energy was primarily determined by the electrostatic forces except under significant deformations, where the van der Waals forces became dominant. The interaction potential energy remained unchanged with specific contact types but decreased significantly due to electrostatic interaction when contacts evolved. As computational capacity develops, a greater number of larger hydrated clay particles can be used to improve simulations of compaction and other macroscopic behaviors via all-atomic molecular dynamics simulations.

Although significant strides have been made in understanding the liquefaction phenomena, the recurrence of catastrophic seismic events continues to underscore the need for critical research in this area. The aim of the paper is to develop a better predictive model for liquefaction that can correctly describe the process of undrained pore pressure buildup in the case of pyroclastic soil. For this purpose, an experimental program was performed through undrained cyclic triaxial tests on three different pyroclastic soils, i.e., Cervinara (Italy), Campi Flegrei (Italy), and Rangiriri (New Zealand). The analyses of the experimental results show the dependency of the mechanism of excess porewater pressures on the stress history, stress state, and stiffness of the investigated soils by using two key parameters, $\psi$ and $\lambda$, derived from the steady-state theory. A new simplified porewater pressure model whose parameters show a functional relationship with the state parameters has been proposed.