Mechanical Failure Mechanisms of Unstable Rock Masses with Sandstone and Mudstone Interbeds as the Base

Based on the comprehensive analysis of the origin and structural characteristics, this study established the physical and mechanical models of an unstable rock mass with sandstone and mudstone interbeds as its base (also referred to as an unstable rock mass with an interbed base) and proposed the retreat mechanisms of the base, i.e., the softening and compressive deformation of mudstones within it induces the tensile failure of the thin-bedded sandstones in it. Moreover, this study explained the sliding-shear and toppling failure modes of an unstable rock mass with an interbed base and put forward the mechanical criteria for the two failure modes. The case analysis showed that the base retreat of the Leijiagou unstable rock mass conforms to the mechanical mechanisms of base retreat proposed in this study and that this unstable rock mass will not undergo sliding-shear or toppling failures under the current situation. The preliminary prediction indicates that the Leijiagou unstable rock mass will lose stability after 15.2 years due to toppling failures, when the critical depth of its rock cavity will be 4.1 m.