Countermeasures against large deformation of deep-buried soft rock tunnels in areas with high geostress: A case study

Abstract Large squeezing deformation has been a main concern in the construction of deep-buried tunnels with soft surrounding rocks in high-geostress areas, threatening the safety of tunnel construction and delaying the construction progress. In this study, the Dapingshan tunnel, where a large deformation occurred, was taken as an example to study this issue. First, the geological and deformation characteristics of the large deformation area were analyzed. Subsequently, the creep model and creep parameters of the surrounding rock in the large deformation area were identified through laboratory tests. Finally, considering the time-dependent effect of tunnel construction, the geostress in the large deformation area was measured using the displacement back-analysis method, and the feasibility of the optimization scheme was verified. The results showed that: (1) The occurrence of large deformation is due to the combined action of the high geostress and poor self-stability of argillaceous sandstone. (2) The creep characteristics of argillaceous sandstone are consistent with the creep characteristics of the CVISC model. (3) The calculation result of the displacement back-analysis method considering the influence of the time-dependent effect of tunnel construction is found to be reliable. (4) The optimization scheme can help reduce the tunnel arch convergence and horizontal convergence by 50% and 60%, respectively, which confirms that the optimization scheme can help eliminate the large deformation of the Dapingshan tunnel.