Abstract: Based on the survey of Gongjiafang, Maoping and Shennüxi bank slopes, there are five stages of disintegration evolution of the quasi-earthy bank slope of Three Gorges Reservoir identified during impounding. These five stages are the formation of bank slope, the development of joint fissures, the formation of argillation interlayer and the quasi-bank slope, the disintegration of the bank slope by impounding, and the follow-up disintegration. On the basis of above disintegration evolution process, a physical model and a mechanical model are developed for the quasi-earthy bank slope disintegration from the viewpoint of fracture mechanics. The stress expressions and formulas of stress intensity factor are developed by considering five different working conditions at different storage levels in the mechanical model. Through the preliminary discussion, some conclusions are drawn as follows. The reservoir storage has a significant effect on the disintegration of the quasi-earthy bank slope. The stress intensity factor of rock block decreases with the increase of the water level. When the water level reaches a level of 4.49 m, fractures in the upper of rock block turn into the bottom, and the of stress intensity factor of rock block increases with rising water level. At the beginning of water storage, the development of fractures is dominated by the gravity of rock block, while the uplifting of water level stabilizes the rock block. The fractures controlled by gravity in the upper gradually change into the fractures governed by buoyancy in the lower part of rock block. The sectional dimension of rock blocks has the significant effect on the disintegration of the quasi-earthy bank slope. Fracture strength factors in the upper of rock block grow with the decrease of ratios of width to height; when the ratios of width to height decrease, fracture strength factors in the lower of rock blocks increase with the increase of the storage levels.

Key words: rock mechanism, disintegration mechanism, fracture interpretation, quasi-earthy bank slope, Three Gorges Reservoir Region