Three-dimensional In-situ Stress Measurement And Stress Field Simulation Analysis Of Mozi Hydropower Station

The large-scale implementation of the Western Development Strategy has enabled the massive use of hydropower resources in the Southwest.In order to make full use of the local high-head and small-flow water resources,the technology of high-pressure diversion tunnel and air cushion surge chamber was introduced in China.During the excavation of related underground chambers such as diversion tunnels,high ground stress can cause problems such as rock bursts in brittle rock masses and large deformations in chambers in soft rock areas,which seriously endanger the safety of construction personnel and engineering quality.And the water permeability of the surrounding rock cracks in the high-pressure chamber will also affect the construction quality and the maintenance cost of the hydropower station later.Therefore,the three-dimensional in-situ stress measurement and high-pressure water pressure test of the surrounding rock of the air cushion surge chamber are important links in the design and construction of hydropower projects.Based on the construction project of Mozi Hydropower Station in Danba County,Sichuan Province,this paper carried out in-situ three-dimensional hydraulic fracturing in-situ stress measurement and high-pressure water pressure test of up to 5 MPa on the air cushion surge chamber of the diversion tunnel using single-circuit double-plug equipment Based on the measured data and the engineering geology and structural geological conditions of the hydropower station engineering area,a regional in-situ stress field simulation study was conducted,and the understanding was as follows:(1)The in-situ stress state of the air cushion surge chamber is measured.The test results show that the maximum principal stress of the surrounding rock of the measuring point is about 15.3MPa,the direction is about NE56 °,the dip angle is about 66 °,and it is nearly vertical;The minimum principal stress value is 6.3MPa,the direction is about SW75 °,and the dip angle is about 33 °,which is a normal fault stress environment;(2)A high-pressure water pressure test was carried out on the joint development area of the air cushion surge chamber,which confirmed that the excavation of the air cushion surge chamber produced a stress unloading circle with a thickness of 5-8m.During the test,the maximum water permeability is 1.27 Lu and the minimum water permeability is 0;under the highest pressure of 5MPa,the maximum water permeability is 0.98 Lu and the minimum is 0.39 Lu.Shows that the air cushion surge chamber has good sealing;(3)According to the engineering geological conditions and regional geological structures in the hydropower station work area,the three-dimensional in-situ stress field simulation was conducted using ANSYS finite element software,a three-dimensional geological model was established,and the magnitude and direction of the maximum principal stress at the measuring point were calculated.The results show close to the measured data;(4)The indoor design maximum pressure of the air cushion surge control is 4.5MPa,and the measured minimum principal stress is 6.3MPa.According to the minimum principal stress criterion,the minimum principal stress inside the chamber is greater than the design maximum pressure and the operation is stable.This basis provides a certain reference basis for the future construction of hydropower stations and fills the gap in the measurement of in-situ stress in the work area.