Mechanical derivation and numerical simulation of sliding angle of loose layer in overlying strata

The surface subsidence is the result of the coupling movement of the overlying bedrock and the loose layer. In essence, it is a mechanical problem. Based on the relevant knowledge of soil mechanics and rock mass mechanics, the mechanical model of loose layer slip fracture is established, the expression of loose layer slip angle is deduced quantitatively, and the structural model of loose layer slip and surface and bedrock fracture position is established. The rationality of the mechanical expression and the reliability of the results are analyzed and verified by numerical simulation experiments and field measurements. The results show that (1) the fracture angle of loose layer is 1/2 of the internal friction angle; and (2) there are two types of loose layer sliding structure: “lower large and upper small” type and “lower small and upper large” type. Then, it forms the composite motion structure types of loose layer: “outer arc,” “inner arc,” “steep-slow-steep,” “slow-steep-slow.”