Evolution Mechanism and Control of Floor Heave in the Deep Roadway with Retained Bottom Coal

Roadways with retained bottom coal are common in thick coal seam mining, and floor heaving is a prominent problem. In this study, based on the interaction between the floor and two sides of the roadway-surrounding rock, a Winkler elastic foundation beam model is established to analyze the floor heave problem. A 3DEC model was used to analyze the failure range, failure mode, and migration law of the floor-surrounding rock with different bottom coal thicknesses and coal body strengths. The results show that (1) an increase in the thickness of the bottom coal results in a decrease in the stiffness of the roadway side coal body (the foundation of the supporting rock layer) and an increase in the bending deformation range, the amount of floor rock beam deformation, and the extrusion force. This leads to an expansion in the range of the sides of the coal body that are squeezed by the floor rock layer, resulting in additional failure and deformation of the coal body sides. Therefore, the damage to the floor rock layer is extended and increased. (2) The expansion of the floor pressure-bearing arch and surrounding rock in the arch are the causes of floor heave in the deep coal roadway with retained bottom coal. (3) Because of an increase in the thickness of the bottom coal and a decrease in the coal body strength, the floor pressure-bearing arch expands to the deeper part; thus, the range of surrounding rock in the arch with deformation and failure increases, resulting in an increase in floor heave. The field practice indicates that the support strategy of the “high prestressed strong rock bolt (cable) supporting two sides and bottom corners in time” can effectively control the floor heave of a roadway with retained bottom coal.