Deformation failure characteristics of weathered sandstone strata tunnel: A case study

Abstract Appropriate countermeasures are required after extreme deformation failure of rock mass to ensure the safety of the tunnel construction and operation, especially in a tunnel that through strongly weathered sandstone strata. The load bearing capacity is further weakened by the permeation of water in complicated geological conditions, which can frequently cause collapse and result in budget overruns during the construction period. This paper provides a case study about the process of the extreme deformation that occurred in the Piancheng Tunnel based on in situ monitoring. Based on the analysis of on-site deformation monitoring data, combined with the engineering practice characteristics, the factors affecting the deformation were analyzed, further, the countermeasures were put forward and its effectiveness was analyzed. The maximum settlement reached 1046.3 mm and the convergence reached 876.4 mm, and the seepage, rock strength and bias load were considered the main cause of extreme deformation. As a means to maintaining the structural integrity, countermeasures such as temporary steel arch, vertical bracing, diagonal bracing and the temporary inverted arch combination were used for strengthening the tunnel’s structure, hence, effectively preventing the development of extreme deformation. The manuscript records the whole process from occurrence to countermeasures of extreme deformation of surrounding rock, which provide experience for future similar projects.