柱状节理玄武岩松弛时空效应及其控制技术

Relaxation time-space effects of columnar jointed basalt and their control technologies

柱状节理玄武岩表现出开挖后易松弛的特性,对白鹤滩水电站拱坝变形和地下洞室群稳定都有重要影响,是该工程的关键岩石力学问题之一。白鹤滩水电站柱状节理玄武岩表现出卸荷松弛、破裂松弛和坍塌松弛3种类型,采用钻孔声波测试为主、钻孔电视全景成像测试为辅的方法开展监测,并建立松弛层划分标准;发现开挖松弛具有显著的时间效应和空间效应;松弛时间效应可用对数函数表征,松弛大致在开挖35 d后趋于稳定,松弛与支护的及时性和有效性密切相关;松弛深度随着洞室跨度、开挖高度和断面面积的增加而不断增大,边墙松弛增幅尤其显著;开挖松弛是岩性、结构面、岩体结构和地应力共同控制的结果;提出成型成套松弛控制技术,取得了良好的控制效果。

It is easy for the columnar jointed basalt to relax after excavation,which has important influences on the deformation of arch dam and the stability of the surrounding rock of underground caverns.Therefore,the relaxation of the columnar jointed basalt is one of the main rock mechanics problems in Baihetan Hydropower Station.It mainly includes three types:unloading relaxation,fracturing relaxation and collapse relaxation.The relaxation of columnar jointed basalt is monitored by using the borehole acoustic wave tests as the main monitoring method and the borehole TV panoramic imaging tests as the auxiliary monitoring method.It is found that the excavation-induced relaxation has significant time effects and space effects.The time effects of relaxation can be represented by the logarithmic function,and the relaxation tends to be stable after about 35 days of excavation.The macroscopic relaxation failure is closely related to timeliness and limitation of support.The relaxation depth,especially for side walls,increases gradually with the increase of the cavern span,excavation height and cross-sectional area.The relaxation of the columnar jointed basalt is the combined effects of lithology,structural plane,rock mass structure and in-situ stress.A series of control technologies are put forward,and good control effects are achieved.