ANALYSIS OF TREATMENT SCHEME FOR SOFT-ROCK LARGE DEFORMATION SECTION IN LONG AND DEEP BURIED TUNNEL

How to ensure the safety of lining structure is a major and arduous problem faced by tunnel builders in Wudu Tunnel, which is caused by the spalling of initial concrete abutments and the shear failure of steel frames in the fractured zone. According to the deep analysis of large deformation and characteristics of soft rock in Wudu Tunnel, it can be found that the main causes of large deformation of surrounding rock are the influences of fault fracture zone and in-situ stress. Based on the field implementation of different support forms and monitoring data, this paper puts forward reasonable support forms and construction schemes for tunnel passing through large deformation section, which includes adjusting support parameters, reducing the face of excavation as well as closing ring of initial support quickly, and replacing blasting excavation with milling machine. In view of the strong rheological characteristics of soft rock, the disorder of stratum structure and uneven distribution of ground stress across fault section, it is suggested that the deformation rate of the first branch before the second lining of tunnel should be less than 2 mm·d^-1, and all construction joints should be set as settlement joints.