Abstract: In order to solve the problem of large deformation of surrounding rock in the parallel heading and main tunnel of Xiaoxiangling tunnel, the mechanical state of the surrounding rock is measured by field test. Based on the obtained data, the causes for tunnel large deformation are analyzed and the targeted control countermeasures are put forward. The results show that: (1) The strength of tunnel surrounding rock is low, and it is obviously anisotropic. The initial geostress is dominated by horizontal stress. It belongs to extremely high geostress. Based on field test results, the damage range of the surrounding rock at the bottom is significantly larger than that at the side. It is inferred to be bottom uplift deformation, which is consistent with the deformation characteristics of the structure in the field. (2) The main reasons for the large deformation are the underlying gently dipping layered weak rock formation, highlevel insitu stress, asymmetry of the structure, and other factors. Especially the asymmetric structure of the parallel heading floor is weak against bottom uplift deformation. (3) The surrounding rock deformation of tunnel is effectively controlled by setting inverted arch in parallel heading tunnel and long anchor bolts in main tunnel, increasing reserved deformation and improving rigidity and strength of the structure.

Key words:  , railway tunnel, Xiaoxiangling tunnel, large deformation of surrounding rock, slight inclined rock strata, bottom uplift deformation, geostress test, countermeasures for large deformation