Abstract: High ground stress soft rock is a common adverse geology in the process of tunnel construction in western mountainous areas of China. This type of stratum is highly susceptible to large deformation disasters during tunnel construction due to the combined effects of higher ground stress and special surrounding rock mechanical properties. The treating ideas and methods for large deformation of tunnel in China and abroad are summarized. Based on the deformation section of the Shengli Village tunnel of the LeshanHanyuan expressway, the causes of large deformation are analyzed according to the characteristics of structural deformation, geological conditions, and monitoring data, and the principles and specific countermeasures for large extrusion deformation in steep rock strata in the Shengli Village tunnel are proposed. The results reveal the following: (1) The large deformation of the Shengli Village tunnel is mainly caused by the joint action of structural stress, weak fracture of surrounding rock, rock dip angle, tunnel trend, and groundwater. (2) The deformation and failure of the steep rock strata exhibit obvious asymmetry and nonuniformity, the bending and inner bulge are easy to occur at the arch, the horizontal convergence is significantly greater than the arch roof settlement, and shows longterm creep characteristics. (3) According to the large deformation treatment idea of "combination of relaxation and resistance", the measures of "onetime excavation, multipletime support, releasing deformation, strengthening surrounding rock, and strengthening structure" have achieved good control effect on the deformation of surrounding rock.

Key words: tunnel engineering, large extrusion deformation, steep rock strata, high ground stress, deformation control