In-Situ Stress Measurement and Estimation in Thrusting Strike-Slip Fault Fracture Zone and Its Significance for Evaluation of the Large Deformation in Fault Fracture Zone

Understanding the in-situ stress field characteristics of rock in fault fracture zone is the basis for identifying large deformation of deep engineering, and can provide key support for understanding the coupling relationship between in-situ stress and regional structure. However, due to the lack of enough measured in-situ stress data, the weakening degree of in-situ stress in the fault fracture zone and its influence on the large deformation have not been reported. We measured in-situ stress in deep holes in a reverse strike-slip fault fracture zone and 5 km intact rock mass on its both sides. Then, the value variation range of in-situ stress in both the fracture zone and the intact rock mass with depth is estimated and compared by analyzing the lateral pressure coefficient analysis method. The result shows that the in-situ stress value of fault fracture zone is significantly lower than that of intact rock mass. As SHf-med ≈ (0.73–0.85) SHi-med in 200–1200 m, we may establish such a mathematical relationship: in large FFZ, at least in RSSFFZ, SHf-med ≤ (0.8–0.85) SHi-med and Shf-med ≤ (0.7–0.85) Shi-med (Z > 200 m). Considering that SHi-med is usually less than (1.2–1.5) SV when Z > 1000 m in and around the Tibet Plateau, whether large deformation occurs in the excavation of fault FFZ in different regions and the same buried depth, and the degree may be mainly affected by the degree of fault fracture, rather than the difference of structural region.