大型洞室分层开挖围岩位移释放率与支护效用探讨

Discussion on Displacement Release Ratio and Supporting Effectiveness of Wall Rock in the Excavation of Large Underground Cavern

针对大型洞室从上往下分层开挖和每一层从一端到另一端沿水平方向分步开挖的空间开挖特点,基于应力反转法研究了大型洞室分层分步开挖过程中不同部位围岩位移释放规律,基于摩尔应力圆法提出了围岩支护效用的定量评价方法。工程实例研究表明,大型洞室顶拱和边墙不同部位围岩在当前层开挖前、开挖过程中和开挖后的位移释放率都不一样;开挖过程中围岩屈服区体积演化是一个与应力释放系数相关的非线性变化过程;不同位移释放率条件下,支护系统对提高围岩强度的作用效用可通过支护前后围岩摩尔应力圆到强度特征曲线的距离来定量表述。

Considering the characters of trenching layer by layer from up to down and tunneling from out to out in every layer in the excavation course of large underground cavern, the displacement release ratio of wall rock is studied based on the stress inversion method, and the supporting effectiveness of supported structure is also quantitatively evaluated based on Mohr stress circle. The case study of an large hydropower underground powerhouse shows that, （a） the displacement release ratios of wall rock in different crown and side position are different before, during and after excavation; （b） the yield volume of wall during excavation is a typical nonlinear process, which is related to the stress release ratio; and （c） the system supporting effectiveness in different displacement release condition can be evaluated by contrasting the distances of Mohr stress circle of supported wall rock to strength characteristic line before and after excavation.