Abstract：Rock slabbing is a serious threat to the construction safety of deep buried tunnels. However，it is still unclear whether rock slabbing is related to the gradient stress in surrounding rocks. In this paper，the changes of the tangential stress gradient with the buried depth increase were theoretically analyzed first. An improved method of rock gradient stress construction was proposed. Then，by the method，strain observation tests were conducted on cuboid granite samples with the d0 (the length difference of upper and lower surfaces of specimen) between 0.1 and 0.8 mm under gradient stress to confirm whether rock spalling can occur under gradient stress and whether the thickness of formed rock slabs are uniform. The results show that the stress changes linearly along the thickness direction of the specimens，with a rate up to more than 103 MPa/m，which means that the improved method can be used to create gradient stress environment in rocks. It is found that the tensile stress in the low-stress region at the end of the specimen，whose direction is consistent with the loading，occurs in the range of 0.5 to 1.5 MPa under gradient stress. The tensile stress presents a “rise-fall-rise-fall” stage change in the process of loading，and it can be restrained by reducing d0. It is confirmed that rock slabbing occurs under gradient stress，and the formed rock slabs have uniform thickness. Moreover，the formed cracks belong to tension cracks，which is consistent with the previous research results. It is also confirmed that the gradient stress is an important factor that cannot be ignored in the propagation process of deep surrounding rock slabbing. This study lays an experimental foundation for further research on the occurrence conditions of rock slabbing and the influencing factors of the thickness of rock slabs.
2022, Vol. 41 
