陡倾结构面影响下巨型地下洞室穹顶开挖围岩稳定性分析

Stability Analysis of Surrounding Rock of The Excavation of The Dome of The Giant Underground Cavern Under the Influence of Steep Dip Structural Plane

白鹤滩水电站地下洞室群规模宏大且围岩地质条件复杂,左岸尾调室洞径达48 m,埋深330 m,受中高地应力、陡倾裂隙、断层等影响,大型穹顶开挖面临着局部高应力区围岩脆性破坏和结构面控制下围岩松弛区变形稳定问题。采用3DEC数值分析软件对多组结构面控制下左岸尾调室开挖过程中围岩变形特征及应力集中程度进行数值模拟,采用三维空间等值面技术分别比较了开挖过程中围岩变形分布特征和应力集中分布特征。研究表明,受大主应力及结构面组合影响,围岩高应力破坏风险不高;但陡倾结构面的存在对穹顶围岩变形有较大影响,围岩变形最大的区域发生在穹顶NW向侧翼区域;陡倾结构面交叉切割使得穹顶局部部位浅层岩体松弛更加突出,易发生松弛坍塌破坏。研究工作的成果可为类似深埋地下工程施工及支护方案的确定提供参考。

The underground cavern group of Baihetan Hydropower Station has a large scale and complex geological conditions.The diameter of the tail chamber on the left bank is up to 48 m and the depth is 330 m.Under influence of medium and high in-situ stress,steep dip fissures and faults,the excavation of large-scale dome faces the problem of the brittle failure of surrounding rock in local high stress area and the deformation stability of surrounding rock relaxation zone under the control of structural plane.The author adopts 3DEC numerical analysis software to numerically simulate the deformation characteristics and stress concentration of surrounding rock during excavation of the tail chamber on the left bank under the control of multiple sets of structural planes.The deformation distribution characteristics and stress concentration distribution characteristics of surrounding rock during the excavation process was respectively compared using three-dimensional isosurface technology.The result shows that,due to the combination of large principal stresses and structural planes,the risk of high-stress failure of surrounding rocks is not high;however,the presence of steep dip structural planes has a greater impact on the deformation of the surrounding rock of the dome.The highest deformation occurs at the flanking area of the dome in NW;cross-cutting of steeply inclined structural planes furthers the relaxation of shallow rock masses in local parts of the dome,and the surrounding rock is prone to slack collapse.The study results can provide a reference for the construction of similar deep-buried underground projects and the design of supporting schemes.