ABSTRACT
Nuozhadu Hydropower Station is located inYunnan province of China. The designed dam height is 258 m. To understand in-situ stress around underground powerhouse, in-situ stress measurements by hydraulic fracturing were carried out.
To understand the plane stress state, in-situ stress measurements by hydraulic fracturing were carried out in two vertical boreholes. The borehole depths are 250 m. In both boreholes the direction of horizontal maximum compression stress is NS~NNE, the maximum compression stress is about 10.0~13.0 MPa, the minimum compression stress is about 7.0~8.0 MPa.
To understand the three-dimension stress state around underground powerhouse, three dimensional in-situ stress measurements by hydraulic fracturing technique were carried at three different sites. In the three sites the directions of maximum principal stress are almost the same, about NNE, and the dip angle is about 10º. The direction of mediate principal stress is almost vertical.
To evaluate the joint rock mass capacity to sustain high water pressure, in other words, what water pressure would induce the joint to open in a long time, hydraulic jacking tests were carried out in 300 m deep borehole near high-pressure tunnel. 6 jacking tests were carried out at different depths, as the rockmass structure is different, the jacking pressures (about 3~7 MPa) were quite scattered.
