Different from single coal seam mining, the stress evolution in the end mining stage of close-distance coal seams is extremely complex. The unreasonable position and support of the lower retracement channel will cause serious deformation and damage to the surrounding rock. Taking the Yanzishan coal mine as the engineering background, the deformation and failure characteristics of the retracement channel under different overlay environments and the key influencing factors of position design were discussed by numerical simulation, theoretical analysis, and field investigation. The results show that the coupling superposition of upper coal pillar high stress and mining dynamic pressure will form a dangerous area with severe ground pressure behavior. The retracement channel should be preferentially designed in zone A (overlying mining roadways), followed by zone B (overlying end-mining coal pillar), and finally, zone C (overlying section coal pillar). In addition, the rational horizontal distance between the lower retracement channel and the upper end-mining coal pillar should make the channel in a good stress environment. The safety distance between the retracement channel and the nearest main roadway (end-mining coal pillar width) should be greater than the severe range of advance abutment pressure. Finally, the design principle and control strategy for the lower retracement channel is proposed. The feasibility and rationality of the study are verified by industrial applications.
In order to determine the reasonable width of a stopping coal pillar in close-distance coal seams, the evolution law of front abutment pressure of the working face with repeated mining was studied. Based on the actual engineering project, we conducted field measurement, theoretical analyses, numerical simulations and a physical similarity simulation test to study. The results show that: (1) according to field measurement, the influence range of front abutment pressure increases from 60 m to 75 m with repeated mining; (2) according to theoretical analysis, the arch height and span are negatively and positively correlated with the influence range of front abutment pressure, respectively; (3) with repeated mining, the arch height increased to 165 m, the arch span to 235 m and the influence range to 83.5 m by 14.5 m relative to that before repeated mining; (4) if it is necessary to ensure that the main roadway is less affected by the mining stress, the width of the stopping coal pillar in 2214 working face should be greater than 80 m. The influence range of front abutment pressure increases obviously with repeated mining in close-distance coal seams. The study provides a reference for similar engineering projects.
In order to mater the reasonable layout basis of the terminal mining line position in the repeated mining of close-distance thick coal seams, taking Yan mine as the engineering background, we conducted theoretical analyses, numerical simulations, and field measurements to study the action mechanism of the stress arch. The results show that (1) with repeated mining, the shape of the left and right half arches of the stress arch changes in the order of time and space until it is stable; (2) the shape of the stress arch is highly related to the distribution of abutment pressure in the working face. If the shape is unchanged, the distribution of abutment pressure is unchanged; (3) in the final mining stage of repeated mining, when the shape of the right half arch is stable, the difference stagger distance of the terminal mining line has little effect on the distribution of abutment pressure of the working face where the front arch foot is located; (4) when the internal stagger distance between 3216 working face and terminal mining line of 4216 working face is greater than 22 m or the external stagger distance is greater than 30 m, 3216 working face is located in a relatively safe position. This study clarifies the key factors for the layout of terminal mining lines in close-distance thick coal seams, which can provide a scientific basis for similar projects.
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