This study evaluates dykes stability of bauxite residue storage facility using limit equilibrium (LEM) and finite element methods (FEM), considering diverse construction phases. In LEM, steady state seepage is simulated using piezometric line while factor of safety (FOS) is determined by Morgenstern-Price method using SLOPE/W. In FEM, actual loading rates and time dependent seepage is modelled by coupled stress-pore water pressure analysis in SIGMA/W and dyke stability is assessed by stress analysis in SLOPE/W, referencing SIGMA/W analysis as a baseline model. Both the analysis incorporated suction and volumetric water content functions to determine FOS. FEM predicted pore pressures are validated against in-situ piezometer data. The results highlight that coupled hydro-mechanical analysis offers accurate stability assessment by integrating stress-strain behaviour, pore pressure changes, seepage paths, and dyke displacements with time. It is found that inclusion of unsaturated parameters in Mohr-Coulomb model improved the reliability in FOS predictions.

Fissured loess slopes along the railway in the Loess Plateau frequently suffer from disintegration disasters under the coupled effects of rainfall and train vibrations, causing soil collapse that covers tracks and severely threatens railway safety. To reveal the disaster mechanisms, this study conducted water-vibration coupled disintegration tests on fissured loess using the self-developed EDS-600 vibration disintegration apparatus, based on the measured dominant vibration frequencies (12-46 Hz) of the Lanzhou-Qinghai Railway. The influence patterns of vibration frequency (f) and fissure type (t) on disintegration rate (S), disintegration velocity (V), and disintegration velocity growth rate (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha_{f - t}$$\end{document}) were systematically investigated, with scanning electron microscopy (SEM) employed to uncover microstructural evolution mechanisms. Results indicate that vibration frequency and fissure type significantly accelerate disintegration: V reaches its maximum at f = 20 Hz, and under the same frequency, V increases with the growth of fissure-water contact area. Under two fissures and f = 20 Hz, V increases by 225% compared to the without vibration and fissures scenario, with the \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\alpha_{f - t}$$\end{document} value peaking at 137.23% and the synergistic effect index exceeding the single-factor superposition value by 45.99%. Microscopically, water-vibration coupling disrupts clay mineral cementation, reconstructs pore networks, and forms dominant seepage channels, leading to reduced interparticle bonding strength, heterogeneous water film distribution, and stress concentration, thereby inducing fractal propagation of secondary fissures and shortening moisture absorption and softening stages. Combined with unsaturated soil mechanics theory, the study reveals a cross-scale progressive failure mechanism involving simultaneous degradation of matric suction, cementation force, and macroscopic strength. A theoretical framework integrating vibration energy transfer, seepage migration, and structural damage is established, along with a quantitative relation linking vibration frequency, fissure parameters, and disintegration velocity. This provides multi-scale theoretical support for disaster prevention and control of railway slopes and foundations in loess regions.

This research presents an in-depth analysis of the volumetric and mechanical behavior of expansive soils surrounding the Khangiran gas well in Sarakhs, emphasizing the effects of matric suction and confining pressures on soil mechanical properties. The study employs both laboratory and numerical approaches, utilizing an unsaturated triaxial apparatus and GeoStudio software, to assess (1) the influence of matric suction and confining pressure on volumetric deformation and shear strength, (2) the impact of annual precipitation on soil swelling, and (3) the tensile stresses exerted on the well casing due to soil expansion. Laboratory results reveal that shear strength increases from 195 kPa to 235 kPa as confining stress rises from 100 to 200 kPa, while cohesion climbs from 68 kPa in saturation to 95 kPa under 100 kPa of matric suction, signifying enhanced resistance in drier soil conditions. Numerical modeling indicates that annual precipitation induces a maximum tensile force of 163 kN at a depth of 13 m, with the expansive zone extending approximately 15 m from the well. The thickness of the steel used for tensile strength resistance against soil swelling is sufficient, and if extensive corrosion of the steel casing is not a concern, tensile strength failure will not occur. These findings offer critical insights into soil-structure interaction in expansive soils and provide practical guidance for the design of resilient gas well casings in similar geotechnical settings.

The occurrence of rainfall-induced slope failures has become more frequent due to the effect of climate change. Hence, various studies have been conducted to analyse the effect of rainfall infiltration on slope stability. Physically-based hydrological models have been commonly used with slope stability models such as the infinite slope model to develop slope susceptibility maps. However, a combination of three-dimensional (3D) water balance model with 3D limit equilibrium method (LEM) has not been commonly used. Hence, in this study, a water balance model, GEOtop was used to investigate the influence of subsurface flow in unsaturated soil under extreme rainfall conditions on regional slope stability in 3D directions. The results from the GEOtop model were used as inputs for 3D LEM slope stability analysis performed using the Scoops3D software to obtain the factor of safety (FOS) map for the region. Four slopes within the region were then selected to be modelled in the twodimensional (2D) seepage and slope stability analyses, SEEP/W and SLOPE/W. Results from the detailed study showed that the pore-water pressures (PWPs) from the 3D water balance analyses were found to be higher than the 2D seepage analyses. Under similar PWP conditions, the FOS from the 2D slope stability analysis was observed to be lower than the 3D analysis for two out of the four slopes. However, the combined 3D water balance and slope stability analyses produced lower FOS compared to the 2D seepage and slope stability analyses due to the higher PWPs in the 3D water balance analyses. Therefore, this study highlights the importance of considering the 3D subsurface flow in unsaturated soil given that it has a significant influence on the FOS of slopes.

Unsaturated soil, as a widely existing soil in nature, has significant differences in mechanical properties compared to saturated soil. Especially when considering water migration and changes, its stability issues become more complex .Therefore, in-depth research on the interaction mechanism and stability of unsaturated soil slopes and support structures is significant. This study first analyzes the mechanical properties of unsaturated soil and the influence of water migration on soil strength based on the principles of unsaturated soil mechanics. It establishes a mechanical model for unsaturated soil slopes. Subsequently, the pseudo-dynamic method was used to simulate the response of slopes under dynamic loads such as earthquakes and rainfall, and the deformation and failure modes of unsaturated soil slopes were explored. Regarding support structures, this article studies the interaction mechanism between retaining walls, anchor rods, and unsaturated soil slopes. A mechanical model of the interaction between the support structure and unsaturated soil slopes was established by analyzing the influence of the support structure on the distribution of soil pressure on the slope, as well as the stability and bearing capacity of the support structure itself. In terms of stability analysis, this article uses numerical analysis methods such as the limit equilibrium and finite element methods to evaluate the overall stability of unsaturated soil slopes and support structures. Suggestions for optimizing the design of support structures were proposed by comparing the stability performance of slopes under different support schemes. The experiment shows that increasing soil cohesion by 1kPa per unit area can increase the stability coefficient by about5%. The interface friction angle between the fill and the wall back increases by 1 degree, resulting in an increase of approximately 7% in the over turning stability coefficient.