板裂结构岩体形成条件与内在成因机制分析

Analysis on Forming Conditions and Internal Causal Mechanisms of Slab-rent Structure Rock Mass

在高地应力区的河谷自然岸坡、人工开挖边坡或基槽以及地下洞室中常可见一类特殊的岩体结构类型——板裂岩体结构,给工程建设有关的这类结构岩体环境的开挖施工和支护带来诸多问题。因此,有必要深入分析板裂结构岩体的基本形成条件与内在成因机制。基于大量工程实践和地质认识,从应力储蓄和释放及地质基础两个方面分析板裂结构岩体的形成条件,地质基础主要包括岩性条件、可形成潜在破裂面的弱面特征,地质历史时期所遭受的构造应力状态等;同时,着重从三个方面论述了地质体受外生作用形成板裂结构的力学成因机制,即应力分异作用、差异卸荷回弹作用或动荷载作用。通过小湾水电站拱坝低高程坝基岩体板裂的实例分析进一步说明开挖施工过程中板裂结构岩体的形成因素。

As a special type of rock mass structure,the slab-rent rock mass structure is often found in natural valley bank slopes,manual excavated slopes or foundation trenches and underground caverns in high crustal stress areas.It brings many problems to the excavation and support in the geological environment.Therefore,it is necessary to deeply analyze the basic forming conditions and internal causal mechanisms of slab-rent structure rock mass.Based on a large number of engineering practices and geological cognition,the forming conditions of slab-rent structure rock mass were analyzed from two aspects:stress saving and releasing,basic geological conditions that mainly includes lithological conditions,weak surface characteristics that can form potential fracture surface,tectonic stress state suffered in geological history period,and etc.The mechanical mechanism of slab-rent structure formed by exogenous action of geological bodies was discussed in three aspects:stress differentiation,differential unloading rebound or dynamic loading.Finally,the forming conditions of rock mass with slab-rent structure during excavation were further illustrated by an example of rock mass slab cracking in the low-elevation dam foundation of Xiaowan Hydropower Station.