IN-SITU STRESS ANALYSIS OF DEEP-BURIED AND EXTRA-LONG HIGHWAY TUNNEL IN NORTHEAST YUNNAN REGION

Prediction of in-situ stress for deep-buried and extra-long tunnel area is always a difficulty encountered by many engineers,while the comprehensive engineering geological analysis presents a unique advantage in evaluating geostress regime of complex engineering projects. Therefore,exemplified by a typical deep-buried and extra-long highway tunnel in northeast Yunnan region,this solution is illustrated and validated. Firstly,based on the tectonic stress field zoning,stress orientations for the targeted area is obtained by analyzing Anderson's theory of faulting mechanics,focal mechanism and statistics of in-situ stress measurement. Secondly,the strength of rock masses for the targeted area is estimated by using Hoek-Brown criterion. The modified Sheorey model then is utilized to estimate the stress magnitudes. The results show that modern tectonic stress plays dominant role in the stress field. The dominant azimuth of maximum horizontal principal stress shows N20°~60°W. The stress orientation for the engineering area maintains relatively stable state. Prediction of stress values indicates that the maximum and minimum horizontal principal stress values respectively score respectively at the values of 11.2~20.5 MPa and 6.6~12.2 MPa,at a burial depth of 500 m approximately. The values reach up to 25.9~28.2 MPa and 15.4~17.1 MPa with a burial depth of nearly 1000 m. It is also pointed that,under such high stress,rock bust or brittle failure of hard rocks can occur in the situation of over 500 meters' buried depth,while large deformation nearly occur in the surrounding rocks masses. The predicted results can be well validated by in-situ stress measurements. The proposed method outperforms traditional ones in predicting stress state of linear engineering projects,and shows a promising application prospect.