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Unlike conventional long-wall mining, the roofing activity is more intense when the long-wall face passes through the abandoned roadway. Technically, the coal pillar between the abandoned roadway and the long-wall face will suddenly fail with a certain critical value of its width, leading to the roof breaks in advance and other production-restricted problems because of the support loss, which will be a great threat to underground mining activities. In order to guarantee safe mining conditions, it is a great necessity to uncover how the roof breaks in advance and how to deal with it. From the stability maintaining of the key block perspective, this study looked at research from the 12404–1 long-wall face of Wulanmulun coal mine, China. The critical value of the coal pillar's width was determined to be about 4.75 m by theoretical analysis, and likely, the appropriate supporting force of the abandoned roadway's roof is about 1073 kN per meter. In this study, a numerical simulation method was adopted to study the ground pressure when the long-wall face is passing through the abandoned roadway. Correspondingly, a compound supporting technology involving the roof presplit technique, anchor cable supporting, and pumping pillar supporting was proposed for the roof of the abandoned roadway, and it practically worked well. [ABSTRACT FROM AUTHOR]

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° 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. [ABSTRACT FROM AUTHOR]