A continuous conversion technology from top coal caving into multi-slice mining for thick bifurcated coal seams

This paper presents a mining technology that enables the continuous conversion from top coal caving (TCC) to multi-slice mining (MSM). The technology helps operations overcome challenges with mining thick bifurcated coal seams, particularly the challenge of rock-parting seams affecting the caving of TCC mining methods. Findings show that the relationship between the rock-parting thickness and the caveability of top coal can be divided into 3 phases, including a complete caving phase, a transition phase, and a stable phase. This continuous conversion technology was applied in the Zhongwei Coal Mine in which TCC was used to extract the initial 260 m of the study area where the rock-parting seam was relatively thin before a transition to MSM was made due to the rock-parting seam becoming significantly thicker. The continuous conversion to MSM involved the working face advancing upward at an angle of 10 degrees until the rock-parting seam could serve as the immediate floor for the upper slice of the coal seam. The rock-parting seam floor also acted as the immediate roof for the working face of the subsequently mined lower slice. The application of this continuous conversion mining technology obtained good application results.

Rupture and Migration Law of Disturbed Overburden during Slicing Mining of Steeply Dipping Thick Coal Seam

Steeply inclined and thick coal seams in Huainan Panbei Coal Mine in Anhui Province, China, were analyzed by physical analog modeling, acoustic emission (AE), and distributed fiber sensing (DBS). The secondary deformation breakage law, sound, and light response characteristics in the rock mass deformation process induced by lower slice mining of steeply inclined coal seams were determined. The results show that the mutation of the hinged rock beam structure in the lower region and the cantilever beam structure in the upper region of the lower slice disturbed overburden is the main cause of the rupture of the workface roof. Based on the AE energy and distributed fiber strain response characteristics, the six stages of disturbed overburden instability in the lower slice and cyclic patterns of steeply inclined coal seams were revealed. The key prevention and control areas of the workface were found to be related to the disturbed high-level immediate roof rupture during the lower slice mining process, rupture of the disturbed main roof, and sliding of disturbed overburden. The three-stage AE positioning morphological characteristics and DBS response stepped jump patterns were analyzed in detail. The research results are considered instrumental in the combined AE and DBS monitoring of deformation and damage of rock and soil structures.