Abstract: To investigate the geological and structural characteristics of the taluslike rock mass, analyze the mechanisms of large deformation collapse during tunnel excavation, and explore the tunnel stability, a case study is conducted of Tayi tunnel of the JianshuiYuanyang highway. Detailed study is carried out on the basic structural characteristics of taluslike rock mass, engineering problems during tunnel construction, and support measures using site survey, field investigation, deformation measurement, and surrounding rock pressure monitoring. The results show the following: (1) The surrounding rock mass has a complex and loose structure, which is easily affected by the excavation perturbation. The influence range of deformation is about 30 m behind the tunnel face. (2) Some disasters such as large deformation, collapse of excavation face, failure of the primary lining, and water inrush are easy to occur after excavation. The surrounding rock deformation and stress increase rapidly due to tunnel excavation, the maximum deformation is about 350 mm, the maximum surrounding rock pressure is 350 kPa, and the internal force of steel arch frame exceeds 250 MPa. It is also found that the excavation of the middle and lower benches can obviously reduce the pressure and deformation around the upper bench. The deformation and pressure along the tunnel section are extremely uneven due to the uniform excavation profile. The safety and stability of tunnel construction in the taluslike rock mass can be guaranteed by enlarging the reserved deformation, improving the type of steel arch and the strength and stiffness of the primary support, installing doublelayer steel arch, strengthening the arch foot support, and implementing advance reinforcement and grouting.

Key words: taluslike rock mass, structural characteristic, tunnel stability, field monitoring, support system