Deformation Movement of Hugely-Thick Conglomerate Stratum in Longwall Top Coal Caving

In the process of longwall top coal caving, the deformation and movement of the overlying hugely-thick conglomerate stratum (HTCS) directly affects the rock pressure behavior in the longwall. Based on conditions of the geology and mining of coal face 13,180 at Gengcun coal mine of Yima Mining Area, China, numerical and similar material simulations were carried out, and the deformation and movement laws of the overlying HTCS were revealed. Based on the geological borehole data of the Gengcun mine field, the structural characteristics of the HTCS and its distribution were studied. With the advancement of the coal face, overlying strata and the HTCS gradually deformed, moved, and collapsed, and deformation range gradually expanded, eventually leading to the separation of the HTCS with its underlying stratum. The numerical simulation results indicated that when the coal face advancement distances reached 155 m, the ratio of caved zone height to mining height of overlying strata was 1.83, the ratio of fractured zone height to mining height was 8.14, and the roof caved angle was 76°. The maximum subsidence at the lower boundary of conglomerate stratum was 11.71 m, and the maximum separation height was 7.3 m. The horizontal movement occurred with the HTCS subsidence, and the horizontal displacement of the observation points on conglomerate strata was related with their horizontal distance from the setting-up room. The horizontal displacement of the conglomerate stratum L(x) was a nonlinear function of the advancing distances C0 of the coal face and the horizontal distances x which was from the measuring point and the setting-up room. The range of horizontal displacement was from − 0.95 to + 1.31 m. The similar material simulation results demonstrated that when the advancement distance of the coal face was 525 m, large-scale separation of HTCS with underlying stratum occurred. The horizontal separation zone reached 409.5 m, and the maximum separation height was 7.7 m. The ratio of caved zone height to mining height of overlying strata was 1.83, and the ratio of fractured zone height to mining height was 9.52. The roof caved angle was 66° on the side of the setting-up room and 62° on the wall side of the coal face. The maximum subsidence at the lower boundary of conglomerate stratum was 12.3 m. When the advancement distance of the coal face was 665 m, the maximum subsidence coefficient of the upper conglomerate stratum was 0.34. Therefore, the upper conglomerate stratum and the ground were still in a state of subcritical extraction. The conclusion provides technical feasibility data for surrounding rock control of the coal face in Yima Mining Area.