Study on the deformation mechanism of chair-like bedding rock landslides under the coupling effect of geological and hydrological factors

Abstract

Chair-like bedding rock landslides are prevalent in the Three Gorges Reservoir area (TGRA), necessitating further investigation into their inducing mechanisms. This study focuses on the Muyubao and Tanjiahe landslides, conducting a comparative analysis of their deformation characteristics and mechanisms while comprehensively considering geological and hydrological factors. The findings indicate that the Muyubao landslide was primarily triggered by the combined effects of rainfall during the water storage period and the rise of the reservoir water levels (RWL), with a threshold of approximately 165 m. In contrast, the Tanjiahe landslide was influenced by a rapid drawdown in RWL, heavy rainfall, and a high RWL, with a threshold of around 175 m. Both landslides exhibited a clear response to the rise in groundwater levels in the steep sections, with significant deformation occurring when groundwater levels reached 175 m (Muyubao landslide QSK1) and 245 m (Tanjiahe landslide QSK2). Notably, variations in landslide morphology, permeability coefficients, and fluctuations in groundwater levels can facilitate the mutual conversion between different landslide types (seepage-driven and buoyancy-driven). To investigate the influence of chair-like slope morphology on landslides, eight landslide models were constructed, featuring a range of dip angles for the rock formation (15° to 30°) and varying length ratios of gentle to steep sections (2:8 to 5:5). The UDEC Code was employed to simulate and analyze the governing effects of slope morphology on landslide deformation and evolution. Through a comparative analysis of the Muyubao, Tanjiahe, Jiuxianping, and Qianjiangping landslide cases, we examined the significant influence of landslide morphology and permeability coefficients on landslide behavior. The results indicate that the length ratio of gentle to steep section is a crucial parameter. When this ratio exceeds 2:8, the landslide is characterized by pushing deformation; conversely, when the ratio is lower, it tends to exhibit overall movement. Additionally, geological factors affect groundwater seepage and water level variation under the influence of rainfall and reservoir water, resulting in distinct deformation characteristics and mechanisms across different landslide types. Factors such as slope angle and the length of the gentle section influence the extent of the submerged area, leading to varied landslide responses to rise of the RWL.