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.