Stability analysis of longwall top-coal caving face in extra-thick coal seams based on an innovative numerical hydraulic support model

The relationship between support and surrounding rock is of great significance to the control of surrounding rock in mining process. In view of the fact that most of the existing numerical simulation methods construct virtual elements and stress servo control to approximately replace the hydraulic support problem, this paper establishes a new numerical model of hydraulic support with the same working characteristics as the actual hydraulic support by integrating numerical simulation software Rhino, Griddle and FLAC3D, which can realize the simulation of different working conditions. Based on this model, the influence mechanism of the supporting strength of hydraulic support on surrounding rock stress regulation and coal stability in front of the top coal caving face in extra thick coal seam were researched. Firstly, under different support intensity, the abutment pressure of the bearing coal and the coal in front of it presents the "three-stage" evolution characteristics. The influence range of support intensity is 15%–30%. Secondly, 1.5 MPa is the upper limit of impact that the support strength can have on the front coal failure area. Thirdly, within a displacement range of 2.76 m from the coal wall, a support strength of 1.5 MPa provides optimal control of the horizontal displacement of the coal.