IN-SITU STRESS STATE AND ENGINEERING EFFECT IN SHANGRI-LA-BANGDA SECTION OF YUNNAN-TIBET RAILWAY

The faults along the Shangri-La-Bangda section of Yunnan-Tibet railway are well developed. The tectonic movement is strong. Research on the present in-situ stress field in this area is conducive to the construction of the Yunnan-Tibet railway. A multisource comprehensive analysis method based on geomechanical trace analysis,focal mechanism solution,and measured data is utilized to analyze the orientation of in-situ stress field of the Shangri-La-Bangda Railway. Based on the Hoek-Brown strength criterion,the modified Sheorey theory and the measured data,the rock mass strength parameters and in-situ stress values along Shangri-La-Bangda section of Yunnan-Tibet railway are estimated and predicted respectively. And the characteristics of in-situ stress field and its engineering effect in the research area are analyzed. The results show that the orientation of the maximum horizontal principal stress is in the range of N0°W~N40°W in the Shangri-La-Deqin stress district while it turns into N60°E~N80°E in the Mangkang-Bangda stress district. The maximum and minimum horizontal principal stresses ranges are 24.23~37.30 MPa and 14.81~22.79 MPa,respectively when the buried depth is about 1 000 m. Their ranges are 47.29~66.69 MPa and 28.90~40.76 MPa when the buried depth is about 2 000 m. The tunnel axes are N80°W~N40°E and N10°E~S50°E in Shangri-La-Deqin stress district and Mangkang-Bangda stress district,which are conducive to the stability of surrounding rock. The effect of high in-situ stress is obvious when the buried depth is more than 400 m. Rockburst risk is high when the depth of hard rock is more than 700 m. Large deformation risk is high when the depth of soft rock is more than 1400 m.