Research on Large Deformation Control of Deep Soft Rock Tunnel Considering Humidity Stress

In order to explore the mechanism of large deformation of deep high-in-situ stress soft rock tunnel and formulate control measures to adapt to large deformation, taking Yuezhishan Tunnel as an engineering background, the Kastner and Caquot formula of deformation pressure and loosening pressure of surrounding rock was first solved, and the analytical solution of moisture stress of surrounding rock was established based on elastoplastic mechanics of rock mass and continuum theory. The convergent constraint method was used to draw the characteristic curves of surrounding rock and initial support under the action of three kinds of surrounding rock stresses, and the interaction law of surrounding rock and supporting structure and the evolution law of the three kinds of stress proportion in the process of section deformation were analyzed. Considering the humidity stress and loosening pressure conditions, the optimal supporting time and supporting parameters of the second lining of Zhishan tunnel are clearly considered, and the optimal supporting scheme is judged by the safety factor F_S of the supporting structure, and the large deformation of soft rock of the tunnel is treated. The results show that: When the radial displacement of surrounding rock reaches 550mm, the pressure P of surrounding rock on the supporting structure is only 0.813 MPa when the deformation pressure P_i is taken into account, and the pressure P increases to 1.372 MPa when the humidity stress P_w and the loosening pressure P_a are taken into account, accounting for 40.7% of the total. The support structure designed only considering the deformation pressure cannot meet the requirements of surrounding rock stability. According to the concept of "pressure relief support", "displacement release peak u_peak=0.325 m" and "spacing D=0.7 m" were determined as the best supporting time and parameters for adding the second layer of steel frame. After 24 days of setting the second steel frame on site, the deformation of surrounding rock converged to 50.8mm, and the large deformation of surrounding rock was controlled. The research results can provide reference for the design and construction of tunnel engineering in the future.