Abstract: The aim of this research is to further understand the law of large deformation during the excavation of deep-buried soft rock tunnels. The chlorite schist section of Xianglushan Tunnel under construction of the Central Yunnan Water Diversion Project is taken as a research background. Constitutive models more suitable for soft rock tunnels are compared and analyzed by using FLAC^3D. The effects of controlling large deformation by the excavation method with reserved core soil step (working condition 1), the pilot pit method on one sidewall (working condition 2) and the excavation method with middle partition wall (working condition 3) are compared and analyzed. Results unveil that the maximum settlement of the vault obtained by Hoek-Brown (H-B) strain softening model is greater than that of the ideal elastic-plastic model, and the error with actual settlement is 9.3%. The vault settlement in working conditions 1 and 3 reduced by about 20% compared with that in working condition 2, and the convergence deformation of arch waist and arch wall in working condition 3 is obviously controlled compared with working conditions 1 and 2. From the perspectives of large deformation control effect and plastic zone distribution, the excavation method with middle partition wall (working condition 3) could effectively reduce the deformation of chlorite schist segment of the tunnel.

Key words: chlorite schist, strain softening model, high ground stress, large deformation, numerical simulation, excavation method