Abstract: To address the large deformation encountered during the construction of the Haba Snow Mountain tunnel on the Lijiang-Shangri-La section of the Yunnan-Xizang railway, the authors employ numerical simulations and on-site monitoring methods to examine the deformation of the tunnel and the stress in the main tunnel area under different advance distances of parallel guiding tunnels. A reasonable advance distance for the parallel guiding tunnels is proposed. The research results indicate the following: (1) The advance distance of the parallel guiding tunnel should be 100 m ahead of the main tunnel, which can achieve a stress release effect of over 90% on main tunnel area by parallel guiding tunnel. (2) On-site monitoring results show that the parallel guiding tunnel reduces the settlement of the main tunnel crown by 6.92%, the horizontal convergence of the upper bench by 14.58%, and the horizontal convergence of the lower bench by 10.8%. Thus, it is evident that the advance excavation of the parallel guiding tunnel can reduce the deformation of the main tunnel support. The control effect on the horizontal convergence of the main tunnel is greater than that on the crown settlement.

Key words: super-deep depth, soft rock tunnel, stress release technology, parallel guiding tunnel, advance distance