Study on Mechanical Evolution Characteristics of Overburden Rock in “Knife Handle†-Type Fully Mechanized Top-Coal Caving Face

Compared with that of equal-length working faces, the mechanical evolution mechanism of overburden rocks in “knife handle†-type mining sites is more complex. The form of roof fracture of knife handle-type mines is more variable, and the stress distribution near the interface is more concentrated, thereby severely threatening the safety of mining. To elucidate the mechanical evolution characteristics of rocks in knife handle-type fully mechanized top-coal caving mining sites, the geological conditions of the 22401 fully mechanized top-coal caving face in Hanjiawa coal mine are investigated. FLAC3D software is used to numerically simulate the abutment pressure, horizontal stress, and vertical displacement of the fully mechanized knife handle top-coal caving face. This provides an effective theoretical and technical framework for subsequent problems, such as mine pressure control, roof management, and support withdrawal under similar mining conditions. The simulation results indicate that when the working face is mined within the range 20–30 m before and after the knife handle caving, the stress distribution is considerably asymmetric, the abutment pressure and horizontal stress are overconcentrated, the maximum vertical stress is 18.41 MPa, and the maximum horizontal stress is 16.45 MPa. Influenced by mining stress and self-weight, the roof subsides and the floor bulges. The maximum sinkage of the roof is 268.9 mm and the maximum bottom drum displacement is 10.01 mm.