Abstract: The direction, magnitude and distribution of in-situ stress are important factors affecting the deformation and failure modes of underground engineering. It is difficult to carry out a lot of measuring test work in the engineering area; the measured results may be of great discreteness. Therefore, it is one of the effective methods to introduce the numerical analysis method and mathematical theory to analyze the in-situ stress field synthetically. This paper is based on the Xianlushan water dispersion tunnel that planned to across the active Longpan-Qiaohou fault, and aims to solve the problem of large discreteness of directional results in measured results. Qualitative understanding of the direction of in-situ stress field is firstly obtained by theoretical analysis and numerical simulation with the existing understanding of the tectonic stress field in China. Based on the test results, the quantitative understanding of the direction and magnitude of the in-situ stress field is obtained by the inversion of the three-dimensional in-situ stress field based on the multiple linear regression. The preliminary results obtained demonstrate that the movement form of Longpan-Qiaohou fault (F10) is mainly consists of normal sliding in conjunction with minor strike sliding. With its influence, the direction of the maximum principal in-situ stress is approximately parallel or small angle intersecting with the trend of F10. The regressed maximum principal in-situ stress for the rock mass near the tunnel will be 13-19 MPa; and the corresponding intermediate principal stress will be 11-16 MPa; and 9-13 MPa for the minimum principal stress. The stress level is relatively high, and presents a trend that > > ( and are the maximum and minimum horizontal principal stresses respectively). F10-1 and F10-2 become the control boundary of the in-situ field, and the stress level between the F10-1 and F10-2 is obviously smaller than the upper and lower rock mass, i.e. 9-10 MPa for the maximum principal in-situ stress, and 7-10 MPa for the minimum principal stress. The maximum principal stress direction of in-situ stress intersects with the longitudinal axis of tunnel with an angle of about 60 degrees, which has a negative impact on the stability of the tunnel.

Key words: in-situ stress, in-situ stress inversion, tectonic stress, multivariate linear analysis