Inversion analysis of the complex initial stress field of an extra-long tunnel based on “overlapping partition-integration”

Abstract

Tunnels in Tianshan are high-altitude highway tunnels, which are extra-long and high-cold. The distribution characteristics of the in-situ stress field of the entire project are crucial to the design and construction of the tunnel. Therefore, this paper first analyzes the hydraulic fracturing in-situ stress test results obtained during the preliminary and detailed survey stages of the engineering area. Second, the inversion of in-situ stress field of the super-long tunnel is proposed based on “overlapping partition-integration,” and a large-scale three-dimensional numerical model with overlapping partition is established. Finally, the in-situ stress field regression of the “overlapping partition-integration,” for inversion and stress field characteristic analysis of the entire engineering area are carried out based on the finite difference method. The results showed that the engineering area is primarily dominated by horizontal tectonic stress in the NNE-NE direction. When the buried depth of the tunnel is less than 300 m, between 300 m and 800 m, and greater than 800 m, the three principal stresses (σH-maximum horizontal principal stress, σh-minimum horizontal principal stress, σZ-gravity stress of overlying strata) showed the characteristics of σH > σh > σZ, σH > σZ > σh, and σZ > σH > σh, respectively. The “overlapping partition-combination” for inversion method of in-situ stress field could provide a reference for inversion of in-situ stress field of extra-long tunnel engineering.