Numerical Analysis of Surrounding Rock Stability in Super-Large Section Tunnel Based on Hydro-Mechanical Coupling Model

The groundwater seepage has an important effect on the stability of tunnel surrounding rock. Considering the effect of seepage, a hydro-mechanical coupling mathematical model is developed based on stress deformation equation of rock mass, flow equation of porous media and relation equation of hydro-mechanical coupling. In connection with the leakage situation of Jiangshuiquan Tunnel with super-large section, a geometry model of tunnel construction is built by COMSOL software platform. Furthermore, the hydro-mechanical coupling model is embedded in the PDE module of the software for numerical simulating the construction process of super-large section tunnel. Consequently, the surrounding rock displacement deformation under is discussed and verified by the data measured in field. Besides, the distribution characteristics of surrounding rock stress, seepage pressure and velocity are deeply analyzed. Results indicate that the displacement calculated by hydro-mechanical coupling model is well consistent with the site monitoring data and is greatly more than that of uncoupling model. After tunnel excavation, stress concentration phenomenon occurs around the cavern, especially at the arch foot part of the outer side wall, so the parts should be viewed as the key supporting part. The groundwater flows into the cavern and the surrounding pore water pressure is unloaded. A large hydraulic gradient occurs in the vault of the tunnel, prone to incur major engineering accidents; while the hydraulic gradient at vault is relatively small and usually has little harmful to engineering safety. The conclusion may provide guidelines for similar tunnel engineering construction.