No abstract

Reasonable roadway layout timing can effectively reduce the deformation of the rock surrounding the roadway and relieve mining and excavation tension. To analyze the mine pressure behavior of the gob-side entry at the edge of a goaf and the roof stability along the strike direction in the middle of a goaf, field observations and particle flow discrete element numerical simulation (PFC) method were performed. The results showed that deformation of the surrounding rock mainly occurred because of roof-to-floor convergence, caused mainly by floor heave. The mechanical behaviors of the rock mass, such as elasticity, fracture, and post-peak softening, could be simulated using the model of a jointed rock mass generated by rigid block elements in the PFC method. Considering the length of the violent and reduced roof activity zones and the activity duration as the indices to determine the basic stability of the goaf, the basic stability distance of the tested goaf edge was 135 m after coal seam mining, and the basic stability time was 27 days. The basic stable distance in the middle of the goaf was 183.4 m after coal seam mining, and the basic stability time was 37 days.

Roof movement induced by coal excavation is the immediate cause of rock pressure redistribution and strata behavior. The rigid block in PFC3D was used to generate a multijointed rock mass, and the PFC3D–FLAC3D coupling model was used to study the movement law of the highly developed structural plane of the overlying strata. Strata movement and abutment pressure redistribution characteristics were obtained. The numerical simulation results showed that the multijointed rock mass model reproduced a rock mass with highly developed structural planes. After coal seam mining, the immediate roof caved and filled the goaf, forming an irregular and regular caved zone. The immediate roof shear slipped along the coal wall. The fracture of the basic roof formed a fractured zone, and the maximum height of the fractured zone first increased and then decreased, exhibiting continuous slow subsidence. The fluctuation of the front abutment pressure was reduced, and the abutment pressure in the goaf jumps was discontinuous. The abutment pressure in the goaf was high in the middle and low on both sides. After the initial fracture of the basic roof, the stress concentration of some rock blocks in the goaf exceeded the in-situ stress, and the average abutment pressure increased with the working face advancing length. With the coal wall of the working face gradually moving away from the goaf, the abutment pressure of the goaf first increased and then remained unchanged; the porosity first decreased sharply and then declined slowly; the coordination number of particles rose sharply and then increased slowly, indicating that the goaf gradually stabilized. Similar simulation results indicated that the variation law of abutment pressure, caving characteristics of the immediate roof, and continuous slow subsidence of the basic roof were the same as those of the numerical simulation.

No abstract