锦屏一级水电站地下厂房围岩变形与破坏特征分析

CHARACTERIZATION OF DEFORMATION AND FRACTURE FOR ROCK MASS IN UNDERGROUND POWERHOUSE OF JINPING Ⅰ HYDROPOWER STATION

结合地质、监测、物探及施工资料,对地下厂房施工期围岩的变形与破坏特征进行分析。分析结果表明,高地应力和低强度应力比条件下,围岩的变形不再主要由地质结构面的张开变形构成,由岩块破坏产生的变形所占比重增加。围岩的变形量级和松弛深度相对较大,边墙的主要松弛深度为12～15m,部分大于15m。围岩变形量级与松弛深度成正比,而松弛深度呈现出渐进扩展的趋势,因此变形的时效性应理解为围岩破坏的渐进扩展过程,与常规的流变概念存在差别。主厂房及主变室下游拱腰部位混凝土喷层鼓胀性裂缝是层状岩体在高应力条件下的卸荷劈裂和向临空面的屈曲破坏的结果,这种破坏导致下游拱脚部位位移测值的增大。主变室上游边墙混凝土喷层裂缝表现为张性开裂,主要原因是母线洞开挖后岩体应力集中导致的岩体压裂破坏。在高地应力条件下,地下洞室群开挖是否可采用"先墙后洞"的施工方案是一个值得探讨的问题。

The deformation and fracture characteristics of the surrounding rock mass are analyzed according to the geological conditions,monitoring and geophysical prospecting data,and construction process.The analytical results indicate that under the condition of high in-situ stresses and low strength-to-stress ratio,the deformation of surrounding rock mass is no longer controlled by the opening displacement of major faults,but by the unloading relaxation of the surrounding rock.The deformation amount and relaxation depth are relatively larger.The main relaxation depth of side wall is between 12 and 15 m,some are even greater than 15 m.The deformation amount increases with the extending of relaxation depth,while the relaxation depth extends with the excavation construction and the passage of time.Therefore the time effect of rock mass deformation should be considered asthe gradual expansion of rock failure,which is different from normal rheological concept.The cracks at the downstream hance of main powerhouse and main transformer house are caused by the unloading splitting and buckling failure of layered rock mass under high stress;and this rock mass failure leads to the increasing of deformation at the downstream hance.While the crack type at the upstream side wall of transformer house is of tensile failure of shotcrete layer,its causes are the compression fracture of rock mass because of stress focus during the excavation of busbars tunnels.Under the condition of high in-situ stresses,whether the scheme as first total excavation of main powerhouse and main transformer house,then busbars tunnels excavation that can be accepted in the construction of underground cavern group is a significant issue.