Study on the Applicability of Various In-situ Stress Inversion Methods and Their Application on Sinistral Strike-Slip Faults

Considering the influence of active faults on an in-situ stress field is of great significance in guiding the construction of tunnel engineering projects crossing active fault zones. Because the traditional multiple linear regression method violates the linear superposition principle concerning unified boundary conditions, a multiple linear regression method with improved boundary conditions for in-situ stress inversion was proposed. However, since the two multiple linear regression methods cannot restore the in-situ stress field, the nonlinear method was proposed to solve the nonlinear problem caused by the irregular ground surface. After obtaining the in-situ stress field of a tunnel in southwest China, the disturbance law of the strike-slip activity of the fault on the in-situ stress field was assessed. The results showed that the inversion accuracy from high to low was the nonlinear fitting method, the multiple linear regression method with improved boundary conditions, and the traditional multiple linear regression method. Their inversion errors were 14.7%, 18.4%, and 19.4%, respectively. The in-situ stress showed a slight upward trend near the fault area and a sudden drop while entering the fault, with an average decrease of 36.3%. Inside the fault, the orientation of the in-situ stress was deflected toward the fault tendency. For sudden strike-slip activity, the in-situ stress was manifested as the stress release outside the fault region with an average decrease of 8.4%. In comparison, the stress inside the fault region tended to increase with an average increase of 11.8%. For continuous strike-slip activity, the in-situ stress was basically unchanged. In addition, the strike-slip activity of the fault caused the in-situ stress to be deflected toward the strike-slip direction.