Abstract
Multi-coal-seam mining creates surrounding rock control difficulties, because the mining of a coal face in one seam can affect coal faces in another. We examine the effects of multi-coal-seam mining on the evolution of the deviatoric stress distribution and plastic zone in the roadway surrounding rock. In particular, we use numerical simulation, theoretical calculation, drilling detection, and mine pressure observation to study the distribution and evolution characteristics of deviatoric stress on Tailgate 8709 in No. 11 coal seam in Jinhuagong mine when the N8707 and N8709 coal faces in No. 7-4 coal seam and the N8707 and N8709 coal faces in No. 11 coal seam are mined. The evolution laws of deviatoric stress and the plastic zone of roadway surrounding rock in the advance and behind sections of the coal face are studied, and a corresponding control technology is proposed. The results show that the peak value of deviatoric stress increases with the advance of the coal face, and the positions of the peak value of deviatoric stress and the plastic zone become deeper. The deflection angle of the peak stress after mining at each coal face and the characteristics of the peak zone of deviatoric stress and the plastic zone of the roadway surrounding rock under the disturbance of multi-coal-seam mining are determined. In conclusion, the damage range in the roadway roof in the solid-coal side and coal pillar is large and must be controlled. A combined support technology based on high-strength and high pretension anchor cables and truss anchor cables is proposed; long anchor cables are used to strengthen the support of the roadway roof in the solid-coal side and coal pillar. The accuracy of the calculated plastic zone range and the reliability of the combined support technology are verified through drilling detection and mine pressure observation on site. This research can provide a point of reference for roadway surrounding rock control under similar conditions.
Highlights
Multi-coal-seam mining is common in China [1, 2], where coal seams that are shallow or have good mining conditions are nearly depleted in a short service life with the continuous increase in coal mining intensity [3]
When the advance coal face is 10 m ahead of Tailgate 8709, the depths of the plastic zone in the roof, solid-coal side, coal pillar, and floor are about 4.0 m, 3.0 m, 3.5 m, and 2.5 m, respectively, and the plastic zone of the shoulder corner of the roadway roof on the solid-coal side extends up to 4.0 m. ese corners are the key areas to control the surrounding rock of Tailgate 8709
Rough a comprehensive analysis of profiles of the peak zone of deviatoric stress and the plastic zone of Tailgate 8709, it is determined that the roadway roof and the shoulder corner of the roadway roof have a large range of damage, which are beyond the support range of ordinary bolts. e roadway roof takes the combined support of Φ18 × 2000 mm bolts, Φ17.8 × 6300 mm single-anchor cables, and truss anchor cables. e singleanchor cable in the shoulder corner of the roadway roof on the solid-coal side is arranged at an angle of 20° on the inclined solid-coal side. e bolt parameters on both sides of the roadway are Φ18 × 2000 mm
Summary
Multi-coal-seam mining is common in China [1, 2], where coal seams that are shallow or have good mining conditions are nearly depleted in a short service life with the continuous increase in coal mining intensity [3]. Ere have been several observational and theoretical studies of the distribution of the deviatoric stress and the plastic zone of roadway surrounding rock. Yu et al [18] deduced the analytical form of the deviatoric stress field of surrounding rock from rock mechanics and other related theories and analyzed the distribution of surrounding rock under different conditions He et al [19] investigated the roof deviatoric stress, surrounding-rock fracture field, and deformation law when changing the width of a large-section open-off cut roof from 6 to 10 m. Ere has been no targeted study on the distribution law of deviatoric stress in roadway-floor surrounding rock disturbed by multi-coal-seam mining. E peak deviatoric stress profile and plastic zone profile of the roadway surrounding rock are determined, and a combined support technology using high-strength and high pretension anchor cables and truss anchor cables is proposed for Tailgate 8709. Is paper considers the effect of multi-coal-seam mining on Tailgate 8709 in Jinhuagong mine, Datong City, Shanxi Province, China. e FLAC3D numerical calculation software is used to study the disturbance mechanisms, deviatoric stress, and plastic zones of the N8707 coal face and the N8709 coal face in No 7-4 coal seam and the N8707 coal face and the N8709 coal face in No 11 coal seam. e peak deviatoric stress profile and plastic zone profile of the roadway surrounding rock are determined, and a combined support technology using high-strength and high pretension anchor cables and truss anchor cables is proposed for Tailgate 8709. e accuracy of the plastic zone and the reliability of the combined support technology are verified by arranging on-site drilling detection and mine pressure observation. is research can provide a point of reference for the control of surrounding rock disturbed by multi-coal-seam mining
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