Transient seepage triggered by rainfall and water level changes has a significant impact on embankment stability. To investigate the effects of rainfall and water level changes on the seepage field of embankments, numerical comparative experiments were conducted based on the Shu River embankment project. The influence of key factors such as rainfall, water level rise and fall rate, and rainfall-coupled water level rise and fall on the internal seepage field of the embankment was analyzed, and the main factors affecting the stability of the embankment slope were identified. The relationship among permeability coefficient, lag rate of the phreatic line, and embankment slope stability factor is explored, and fitting equations are developed. The results show that rainfall infiltration increases the pore water pressure of the soil, leading to a decrease in the effective stress of the soil and a decrease in the slope stability factor. The stability factor of the embankment slope is positively correlated with the rise and fall of the water level, and the faster the rate of rise and fall, the higher the rate of change in pore water pressure. The stability factor of the embankment slope showed a trend of decreasing and then increasing with the decrease in water level, and when the water level had decreased by 70%, the lag rate of the phreatic line was the largest, and the stability factor of the embankment slope was the lowest. The established equations for fitting the stability factor of the embankment slope to the lag rate of the phreatic line can be used as a reference for the safety assessment of similar embankment projects.

The influence of a firm stratum on the stability of a slope under undrained conditions has long been of interest to geotechnical investigators, which has been studied in a number of previously important works in relation to slope stability analyses without considering soil spatial variability. This paper proposes another look at such a problem in the context of probabilistic slope stability analyses considering soil spatial variability. Here, the random field (RF) is used to simulate the spatially variable undrained soil strength. It is found that under stationary RF and non-stationary RF with the soil strength at the top ground surface (s(u0)) larger than 0, the depth of the firm stratum (H-f) has a significant influence on the mean and standard deviation of factor of safety (i.e., mu [FS] and 6 [FS], respectively). By contrast, under non-stationary RF with s(u0) = 0, H-f has a slight influence on mu [FS], but its influence on 6 [FS] is non-negligible. In addition, the autocorrelation distance is found to have an insignificant impact on the influential effect of H-f f on mu [FS]. However, for 6 [FS], this impact is not negligible. When the autocorrelation distance is smaller, the influence of Hf f on 6 [FS] would be more significant. Under non-stationary RF, the influence of H-f on 6 [FS] would be slight if the autocorrelation distance is large enough. Furthermore, the impacts of slope ratio, su0, u0 , isotropic and anisotropic features on the influential effects of H-f are also investigated and discussed.

The rock-soil mass, subjected to complex and lengthy geological processes, exhibits heterogeneity which induces variations in mechanical properties, thereby affecting the overall stability of slopes. In this paper, a novel numerical model that incorporates the Weibull distribution function into the meshless numerical manifold method based on the strength reduction method (MNMM-SRM) to account for the slope soils heterogeneity and their influence on the factor of safety (Fs) and the critical sliding surface (CSS). Initially, the Weibull distribution is introduced into the MNMM-SRM model based on the complementary theory of subspace tracking, addressing the issue of multiple yield surface corners in the Mohr-Coulomb framework while simultaneously considering the heterogeneous nature of rock and soil formations. Subsequently, an intelligent method based on unsupervised learning is proposed to obtain reasonable CSS, utilizing the total displacement field at slope nodes and the equivalent plastic strain field as input variables. The results serve as criteria for terminating the strength reduction in the MNMM-SRM. The applicability of this method is verified through three typical examples, demonstrating its potential for widespread application in the assessment of heterogeneous slope stability.

Among various available methods for slope analysis, the limit equilibrium method is very popular because of its simple concepts. The limit analysis method and the finite element method (FEM) also can perform stability analysis of a slope. Increasing computing power and the easy accessibility of inexpensive numerical modeling codes have made the finite element method a very attractive tool for the practical assessment of slope stability. The present study reports the results of slope stability analysis of a few problems analyzed using a developed program utilizing FEM. This program employs a strength reduction technique based on FEM. Mohr-Coulomb strength criterion of soil is used for predicting the stress state, while the viscoplastic algorithm is used for stress redistribution. Non-convergence of the algorithm to achieve the desired equilibrium of all forces in the system is adopted as a marker of slope failure. Further, to put the proposed method to the test, a few examples from the literature are analyzed using the developed program. The example problems cover a homogenous slope with water loading, an inclined layered slope, and a staged embankment subjected to different forms of loading including earthquake forces, pore water pressure, external water pressure, etc. The results of each analysis are compared with other researchers work, and it is found that the obtained results are in good agreement. Deformed mesh, equivalent viscoplastic strain contour plots, and failure function contour plots are used for illustrating the failure state.

Under the combined effect of rainfall and water level fluctuation, the slope of the reservoir bank is prone to collapse. Ideal elastic-plastic Mohr-Coulomb criterion is used to analyze the stability of reservoir slope, which is difficult to characterize the complex mechanical characteristics of slope soils, such as over consolidation dissipation under wet-dry cycles. It is difficult to analyze the stability of bank slopes under the action of dry and wet cycles to reflect the complex mechanical properties such as overconsolidation and dissipation of slope soils. In this study, focusing on weakly overconsolidated unsaturated red clay at the reservoir bank slope of the Xingan shipping-hydropower junction project in Jiangxi Province, unsaturated direct shear tests were conducted and an overconsolidated unified hardening (UH) model for red clay was constructed. The UH model incorporates the mathematical-physical relationship between suction stress and matric suction using the arctangent function. Subsequently, based on the UH model, an application program of FLAC3D was developed in C++. The SEEP/W module of GeoStudio software was employed to compute the unsaturated seepage field during the rainfall infiltration, and an interface program was created to import FLAC3D data for stability calculations of the reservoir slope. Comparisons between the horizontal displacements obtained from the improved UH model and the classical unsaturated elastic-plastic model revealed significantly larger displacements in the former, suggesting that the improved UH model can provide reasonable predictions of the overconsolidated unsaturated red clay for reservoir slope stability. This research offers valuable insights for similar projects involving analyses of reservoir bank slope.

The September 6, 2018, earthquake in the eastern part of Hokkaido, Japan, caused extensive slope failures in Atsuma-town, Hokkaido, Japan. In this study, the authors performed in situ investigations, including trenching and portable dynamic cone penetration tests, on weathered fallen pumice sediments, which are one of the causes of the slope failures. In addition, we performed direct box shear tests on undisturbed samples collected from an undisturbed area under various shear conditions to characterize mechanical properties of the soil. The parameters obtained from the mechanical tests were used to evaluate slope stability under normal and seismic conditions with an infinite-length slope model. The results showed that the slopes where seismic failures occurred had a fragile layer from the surface to a depth of approximately 1.5 m, which generally corresponded to the depth of failure. Weathered pumice deposits with extremely high-water content existed at the boundary between the weak layer and the basement layer, and their shear strength was velocity dependent. It has been shown that an infinite-length slope stability analysis can be performed by using mechanical parameters for which velocity dependence of horizontal acceleration and shear strength due to seismic motion are accounted for.