Landslides frequently occurred in Jurassic red strata in the Three Gorges Reservoir (TGR) region in China. The Jurassic strata consist of low mechanical strength and poor permeability of weak silty mudstone layer, which may cause slope instability during rainfall. In order to understand the strength behavior of Jurassic silty mudstone shear zone, the so-called Shizibao landslide located in Guojiaba Town, Zigui County, Three Gorges Reservoir (TGR) in China is selected as a case study. The shear strength of the silty mudstone shear zone is strongly influenced by both the water content and the normal stress. Therefore, a series of drained ring shear tests were carried out by varying the water contents (7%, 12%, 17%, and 20%, respectively) and normal stresses (200, 300, 400, and 500 kPa, respectively). The result revealed that the residual friction coefficient and residual friction angle were power function relationships with water content and normal stress. The peak cohesion of the silty mudstone slip zone increased with water content to a certain limit, above which the cohesion decreased. In contrast, the residual cohesion showed the opposite trend, indicating the cohesion recovery above a certain limit of water content. However, both the peak and residual friction angle of the silty mudstone slip zone were observed to decrease steadily with increased water content. Furthermore, the macroscopic morphological features of the shear surface showed that the sliding failure was developed under high normal stress at low water content, while discontinuous sliding surface and soil extrusion were occurred when the water content increased to a saturated degree. The localized liquefaction developed by excess pore water pressure reduced the frictional force within the shear zone. Finally, the combined effects of the slope excavation and precipitation ultimately lead to the failure of the silty mudstone slope; however, continuous rainfall is the main factor triggering sliding.

The time-dependent deformation behavior of silty mudstone brings pronounced difficulties for the construction and maintenance of slope engineering, which has attracted much attention. This study examines the creep characteristics of silty mudstone through multistaged loading tests and studies the creep-induced microstructural evolution using Scanning Electron Microscopy (SEM). To mitigate the variability caused by natural defects in the rock, similar material specimens were prepared to substitute silty mudstone for experiments. The results demonstrate that creep strain escalates stepwise with stress level, with the magnitude of each increment being contingent upon the applied confining pressure (sigma 3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sigma _{3}$\end{document}). The strain rate undergoes three phases including attenuation, stabilization, and acceleration. Cumulative strain correlates positively with sigma 3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sigma _{3}$\end{document}, while the initial creep rate declines before slightly increasing. Creep failure predominantly manifests in a shear pattern, with sigma 3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sigma _{3}$\end{document} controlling the development of fractures in terms of their length, number, and angle. SEM analysis reveals that increased sigma 3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sigma _{3}$\end{document} facilitates the expansion of transgranular cracks, displaying a coupled ductile-brittle fracture mode. Furthermore, sigma 3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sigma _{3}$\end{document} variably affects the micropore morphology (pore size, area, roughness, and regularity), with the differences in pore structures under various sigma 3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$\sigma _{3}$\end{document} being distinguished by the fractal dimension. Also, the fractal dimension is positively correlated with porosity, which can be quantitatively characterized using a nonlinear logarithmic function. The interaction between particles and cement, coupled with the development of cracks and pores, is identified as the primary mechanism of structural failure during the creep process.