Technical mechanism of arch-shaped face in controlling strong mining pressure for LTCC panel with weakly cemented overburden

The weakly cemented overburden in thick coal seams exhibits significant mining disturbance effects, characterized by low rock strength, water-induced disintegration, and highly developed fractures. These factors lead to intense overburden movement and frequent occurrences of high ground pressure. To mitigate hazards at the source of weakly cemented overburden in thick coal seams, this paper uses the 1101 working face of Zhundong No.2 Mine as the engineering background. It employs theoretical analysis, laboratory testing, numerical simulation, and on-site measurements to investigate the macro and microstructural characteristics and strength properties of weakly cemented overburden, the mechanisms generating strong ore pressure in large-height complex faces, and methods for source control. The findings reveal that the weakly cemented overburden rock is primarily soft rock with a strength of less than 30 MPa, severely affected by calcareous erosion fissures. Pores are developed between fine grains, and there is an absence of cemented filler. Following coal seam mining, the intense movement driven by fractures in the weakly cemented overburden results in excessive mining pressure at the working face, frequent hydraulic support failures, and coal wall sloughing. A fracture-containing basic roof structure model was established, elucidating the instability mechanism of the basic roof structure under the combined effects of calcareous erosion fractures, weakly cemented rocks, and water infiltration through fractures. Utilizing field-measured data on calcareous erosion fractures and Discrete Fracture Network (DFN) meshing technology, the ultra-thick sandy mudstone layer overlying the basic roof was reconstructed. Through key block theory, the distribution and proportion of movable blocks within the massive rock stratum were identified. High-proportion, large-sized vertically subsiding blocks rapidly load destabilized basic roof fracture blocks, leading to high-static and dynamic loading phenomena at the working face. An arch-shaped layout for longwall top coal caving mining was proposed, accompanied by a design for the processes of arch face formation. An arch-shaped roof structure model was developed, revealing the stress rotation trajectory induced by mining activities. The arch-shaped working face modifies the structural morphology of the weakly cemented roof and the load transfer path of the overlying strata, enhancing the bearing capacity of the weakly cemented roof, eliminating the influence of calcareous erosion fractures, and reducing the degree of advanced mining-induced stress concentration. The arch-shaped face control technology for high ground pressure has successfully achieved source governance of roof disasters in the working faces of ultra-thick coal seams with weakly cemented overburden. Both support resistance and microseismic energy release from the overlying strata exhibited a decreasing trend, significantly enhancing the effectiveness of surrounding rock control. The research findings can serve as a reference for managing high ground pressure during the safe mining of thick coal seams under similar conditions.