Distribution characteristics and inversion analysis of in-situ stress field in tunnel site of extra-long and extremely deep tunnel in Wumeng Mountain area

[Objective]In-situ stress is the core basic data for the construction and design of tunnel engineering. In order to accurately obtain the distribution characteristics of the initial in-situ stress field in the tunnel site area, aiming at the Qiaojia extra-long and extremely deep tunnel project of Ludian-Qiaojia Expressway, according to the test results of in-situ stress hydraulic fracturing method in the tunnel site area, the distribution law of three-dimensional in-situ stress field in the tunnel site area is analyzed. [Methods]Combined with the numerical simulation inversion method, the displacement boundary, stress boundary, mixed boundary and boundary conditions based on the initial strain energy theory are compared and analyzed. The inversion results show that the inversion method based on the initial strain energy theory can better simulate the initial stress field. Based on the existing geological conditions, a three-dimensional geomechanical model is established. The optimal boundary conditions obtained by the finite element method are applied to the in-situ stress inversion analysis of the overall model of the tunnel site area. The inversion value is compared with the measured value to further verify the rationality of the inversion method. [Results]The results show that the in-situ stress test results show that the principal stress value increases approximately linearly with the increase of buried depth. The overall law is as follows : the maximum principal stress(SH) > vertical stress(SV) > minimum principal stress(Sh), and the dominant direction of the maximum principal stress is NW32°. The initial stress field in the tunnel site is mainly horizontal tectonic stress. The numerical inversion results show that the inversion value is in good agreement with the measured value, the relative error is within the allowable range, and the inversion law is basically consistent with the actual stress field law. The in-situ stress field obtained by this method is reasonable and reliable. [Conclusion]The research results can provide basic theoretical basis and engineering reference for in-situ stress field inversion of deep buried tunnels.