Initial ground stress field regression analysis and application in an extra-long tunnel in the western mountainous area of China

Abstract

The understanding of the initial ground stress field in a deep and long tunnel can help to optimize the support structure design and reduce the occurrence of collapse and other failures in tunnel construction and operation periods. Daxiangling Tunnel is a deep and long tunnel under multiple faults condition, many collapses, rock bursts, and large deformations occurring during construction. This paper presents a study of initial ground stress field regression analysis in Daxiangling Tunnel. A three-dimensional geomechanical model with faults is established first, which satisfies the deformation compatibility equation at the fault location. Then, according to the superposition principle, the distribution of regional stress field under the fault condition is obtained by the method of partition inversion. The results show that the distribution of the ground stress field in the Daxiangling Tunnel areas is mainly tectonic stress. The horizontal stress in the area is greater than the vertical stress, and the extreme value appears at the maximum excavation depth. Owing to fault extrusion shear, the stress relaxation exists in the stratum near the fault. The regression analysis results are generally consistent with the measured results, and the relative error is controlled within 10%. However, owing to the boundary effect of the finite element model, the regression stress values near the tunnel entrance and exit are distorted. This can be corrected by applying a mathematical statistical method to obtain the initial stress field of the Daxiangling tunnels with higher applicability.