三峡库区蓄水期间类土质岸坡断裂解体机制研究

Fracture disintegration mechanism for quasi earthy bank slope during impounding in Three Gorges Reservoir

以龚家方、茅坪、神女溪岸坡为例,总结了三峡库区类土质岸坡蓄水解体演化的5个阶段:岸坡形成阶段、节理裂隙发育阶段、泥化夹层及类土质岸坡形成阶段、蓄水作用岸坡解体阶段以及后续解体阶段。根据上述演化过程,从断裂力学角度建立了类土质岸坡解体的物理模型和力学模型,该力学模型考虑了5种蓄水工况下的受力状态,推导了相应的应力表达式和断裂强度因子公式。初步探讨得出以下结论:水库蓄水对类土质岸坡解体影响较为显著,岩块断裂强度因子随着蓄水位的升高而不断递减,蓄水水位升至4.49 m时,岩块断裂趋势由上部断裂转为下部断裂,断裂强度因子随着水位增高而增大。蓄水伊始,岩块重力对断裂起主要作用,而水位抬升起到一定的稳定作用;水位继续抬升,由重力主导的上部断裂逐渐转化为由浮托力决定的下部断裂。岩块的截面尺寸对类土质岸坡解体具有重要的影响。当岩块上部断裂时,断裂强度因子随着宽高比的减小而增加;当岩块下部断裂时,随着宽高比的减小,岩块断裂强度因子随蓄水位的增加而增大。

Based on the survey of Gongjiafang, Maoping and Shenntixi 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.