Back analysis of three-dimensional initial geostress Laxiwa underground powerhouse

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.