拉西瓦水电站地下厂房三维高地应力反演分析

Back analysis of three-dimensional initial geostress Laxiwa underground powerhouse

拉西瓦水电站厂房地处峡谷山高坡陡,河谷狭窄,区域地应力场较高,局部存在构造破碎带,同时开挖尺寸规模巨大,围岩主要为脆硬的花岗岩,对洞室稳定极为不利。为了评判开挖后围岩的稳定及支护设计的长期安全,需要对围岩的岩体力学参数和初始应力场进行反演确定。首先,利用现场初始地应力的实测值反演大范围内的岩体构造地应力场分布,然后,利用洞室分层开挖扰动下,厂房上部关键点实测位移检验并修正反分析地应力结果,得到了较为准确的三维地应力分布,为后续地下厂房开挖围岩的稳定性及支护设计和长期安全的评价与预测,提供了基础数据,有效地指导了厂房开挖施工。厂房开挖完成后的围岩位移的实际监测结果与采用反演地应力场与岩体参数得到的厂房围岩位移值的一致性表明,地应力场反演结果与实际地应力值一致。

Laxiwa Hydropower station is located in a high mountain valley and narrow valleys, where the regional geostress field is higher. Besides, local existence of tectonic fracture zone and size of large-scale excavation are common phenomena in this project. The surrounding rock of hydropower plant is mainly granite, which are hard and brittle rock, this kind of rock is very detrimental to the stability of the cavern. In order to judge the stability of surrounding rock after excavation and long-term security of support design, it is need for obtaining mechanical parameters of surrounding rock mass and the initial stress field. Based on the measured values of the initial stress in-situ, rock tectonic stress field distribution of large-scale rock mass is obtained through back analysis; then using displacement of the key point, measured at the top of stratified cave excavation disturbance, obtain the more accurate three-dimensional stress distribution results. For follow-up excavation of underground powerhouse, evaluation and prediction of stability of surrounding rock and long-term safety of support design, the basic data are provided for effectively guiding the following excavation of plant. Displacements of surrounding rock after the completion excavation obtained by using rock mass stress field parameters of the plant are consistent with the actual monitoring results of surrounding rock displacement; it is shown that the geostress field back analysis results are consistent with the actual values of the geostresses.