Abstract
The Three Gorges Reservoir area features widespread, thick, and well-developed Jurassic soft and hard strata, leading to complex deformation, failure modes, and instability mechanisms on slopes. This can result in collapse disasters. Focusing on the Zigui Basin in the Three Gorges Reservoir area, our study investigated the topographic and geomorphological characteristics of both artificial and natural slopes, the thickness of soft and hard phases, crack expansion, and established a geomechanical model for slope collapse in the Jurassic formations. Utilizing UDEC7.0 software, we conducted numerical tests to analyze the impact of various factors such as slope angle, rock formation inclination angle, slope height, ratio of hard and soft rock thickness, structural surface strength, and mechanical parameters of rock formations on slope stability. Through numerical simulations based on the geomechanical model, we examined the mechanisms of slope collapse and instability in the Jurassic strata, ultimately developing a model for slope deformation and failure. The research findings indicate that geomechanical modes of slope failure in soft and hard strata can be categorized into three types: push collapse, slip collapse, and toppling collapse. Upon analysis, it is observed that model No. 1 demonstrates push collapse, while model No. 6 experiences slip collapse. Model No. 19 ultimately succumbs to toppling collapse. The inclination angle \(\beta\) of the rock layer significantly influences the instability and failure mechanism of slopes in soft and hard strata. Specifically, when the slope aligns with the direction of the slope and \(\beta\)<\(\alpha\), failure occurs initially through layer creep followed by shear slip. Conversely, when \(\beta\)>\(\alpha\), the upper rock mass experiences layer slip while the lower rock mass undergoes buckling deformation. In the case of the slope facing in the opposite direction, a small \(\beta\) results in toppling deformation, whereas a large \(\beta\) leads to local collapse at the slope's peak. Different failure modes exhibit distinct crack development patterns. Under the influence of gravity load, push collapse progresses from internal micro cracks to the downward pushing and destruction of the rock layer. Slip collapse is characterized by cracks initiating at the front edge and extending to form a “z”-shaped penetration. Toppling collapse involves the appearance of local micro-cracks at the slope's upper portion, gradually propagating along the slope surface from top to bottom. The process of different failure modes can be divided into three stages: an initial creep stage before approximately 21g, a steady-state deformation stage between 21g and 40g, and an instability collapse stage after around 40g.