Study on supporting time of tunnel lining in thin-layered rock mass

Abstract

The thin-layered rock mass of Baokang tunnel has the characteristics of large deformation and failure of soft rock under the excavation unloading. More seriously, a serious question is that the lining cracking is prominent. The cause of the cracking can be traced to different failure modes of the surrounding rock mass. Specifically, the rock layer on left arch spandrel is prone to bending failure due to the action of tangential stress, while the right-side wall is prone to sliding failure due to the action of higher shear stress. Furthermore, the lining cracking may beyond the ultimate compressive capacity when the loosely collapsed rock mass acted on the lining. According to the transversely isotropic characteristics of layered rock mass, the failure approach index (FAI) was selected to evaluate the damage and failure of thin shale. Meanwhile, the result of the example shows that this index can effectively characterize the failure characteristics of the thin-layered rock mass. Hence, the FAI was used as an evaluation index of the loose failure of layered rock mass. In order to determine the lining support time, the stability of the lining under the action by the loose rock mass was analyzed by the numerical simulation. As a result, the distance between the lining and the face should not be bigger than 120m. According to the Feedback through onsite construction, the lining cracks didn’t appear under this supporting time, which ensured the stability of the lining structure. The research methods and ideas can provide reference for the similar tunnel lining construction in thin-layered rock mass.