Study on the Stability of Tunnel in Weak Surrounding Rock Considering Initial Support Parameters and Excavation Method

The deformation control of surrounding rock is a crucial aspect in the design and construction of tunnels that traverse weak geological formations. This study developed a three-dimensional numerical model of tunnel excavation that accounts for the hysteresis of initial support, based on a highway tunnel under construction in Ganzhou, China. The rationality of the numerical model was verified through on-site measurements, and orthogonal tests were conducted to analyze the impact of construction parameters on the deformation of surrounding rock. The research findings indicate that the pipe-roof can be divided into four longitudinal sections according to the distribution of stress state: the tension section ahead of the entrance casing arch, the compression section behind the tunnel face, the tension section ahead of the tunnel face, and the compression section at the rear end of the pipe-roof. The grouting reinforcement can restrict the generation and development of plastic zone in the arch of surrounding rocks, which reduce the vault settlement significantly. The primary and secondary order of the impact on tunnel vault settlement, side wall convergence and surface uplift are excavation method, pipe-roof grouting radius, initial support thickness, pipe-roof layout range.