Stability Characteristics and Support Design of Roadway Roof Contained Multiple Soft Inter-layers

We establish mechanical model of hard layered compound roof contained multiple soft inter-layers at mine roadway, and analyze the structural characteristics, failure mechanism and criterion for roof separation. Based on key strata theory, combination beam theory and suspension theory, we present the calculation method of anchorage parameters about roof. The study shows that the roof separation leads to stiffness degradation of compound roof and results in subsidence, rupture, and caving of roof. The major influence factors of layer separation in roof are differences of bending deflection of different strata. The roof combination rock beam by bolt anchoring needs enough combined strength, otherwise, it easily occurs bed separation between combination rock beam and main roof, makes the rock beam to produce bending fracture or shear failure at two ends, and form simply supported beam structure, and at last, the rock beam caving. The reasonable design of roof anchorage parameters, especially pre-tightening force, plays an effective role in control roof instability.