Stability Analysis and Deformation Control of Tunnel with Extremely Weak Surrounding Rocks Caused by Strike-Slip Fault Activity.

With the rapid rise of infrastructure construction in southwestern mountainous areas of China, tunnel engineering has become increasingly frequent in crossing faults with strong activity. However, there has been a long-term lack of an effective theoretical method for identifying the stability and controlling the deformation of extremely weak surrounding rocks inside active faults. Therefore, this paper researched stability analysis and deformation control of a tunnel with extremely weak surrounding rocks caused by strike-slip fault activity. Firstly, uniaxial and triaxial compression tests were conducted on completely decomposed granite within active faults under drained and undrained conditions, and the mechanical properties of granite after desertification and argillization were analyzed. Then, based on the upper-bound limit theory and according to the relationship between the safety factor, instability trace, and geo-stress, a theoretical method to evaluate the stability of the unsupported surrounding rock under different geo-stress levels was proposed. Furthermore, a comprehensive deformation control method, including advanced support, excavation face reinforcement, and radial grouting, was proposed, and the applicability of this method was analyzed and verified through field mechanics and deformation measurements. The results showed that under the triaxial stress state, the post-peak stress drop characteristics of completely decomposed granite basically disappear, and the plastic deformation characteristics of rock become prominent. The comprehensive strengthening scheme has a significant deformation control effect, and the surrounding rock deformation can be reduced by over 65%. In addition, the pressure on the supporting structure will be more than 3.2 times higher with no reinforcement scheme. Highlights A comprehensive deformation control scheme has been proposed to prevent and control deformation disasters in extremely weak surrounding rocks caused by strike-slip fault activity. An upper-bound limit theory considering the influence of geo-stress is established to judge the stability of the unsupported surrounding rock. The mechanical properties of completely decomposed granite caused by strike-slip fault activity under drained and undrained conditions are analyzed. [ABSTRACT FROM AUTHOR]