Abstract

Close seam group mining under thin immediate roofs and thick sandstone walls is typically performed with a strong mine pressure and gas concentration, which pose considerable risks to miners. In this study, the mechanism of pressure relief and permeability enhancement to enhance gas extraction for mining safety through blasting roof cutting were investigated through theoretical analyses, numerical simulations, and laboratory tests. The results revealed that, near the blast-hole, which produced numerous cracks, blasting disturbed the integrity of the thick-layer roofs and redistributed the stress near the blast-hole, which prevented violent mine pressure caused by excessive fracture distances on the thick and hard roofs, reduced the additional load on the support, increased vertical gas migration, and ameliorated the effect of gas drainage caused by high-level boreholes. The field applications of forced roof cutting through deep-hole blasting in the II 7224N face of the Renlou coal mine (Huaibei, Anhui, PR China) demonstrated that the occurrence of excessive pressure on the fully mechanized mining hydraulic support was prevented. The gas extraction volume of high-level boreholes was maintained at 6–8 m3/min; the extraction concentration was stable at approximately 35%; and the gas concentration in the upper corner of the coal face was lessened from 7% to <1%, which ensured normal mining in the coal face. The current results can provide data reference and a theoretical basis for roof management and gas control of the same type of coal face.

Highlights

  • The main factors in the safe mining of close coal seams under thick sandstone are roof stability and gas control

  • To more intuitively observe the crack expansion and development of deep-hole blasting under the condition of a thick and hard roof, a similar simulation test was carried out according to actual coal, and rock conditions were obtained from the II 72 24N coal face of the Renlou coal mine

  • Under the action of the detonation stress wave, plenty of cracks were generated in the rock and the thick and hard roof collapsed as desired in time, which were generated in the rock and the thick and hard roof collapsed as desired in time, which alleviated the range of the suspended ceiling and reduced the roof fracture step distance and alleviated the range of the suspended ceiling and reduced the roof fracture step distance the periodic pressure step distance of the coal face

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Summary

Introduction

The main factors in the safe mining of close coal seams under thick sandstone are roof stability and gas control. Forced roof cutting through deep-hole blasting is used to weaken hard roofs without accidents such as gas overruns because no prominent crack is developed in the roof. Affecting normal mining so that the thick hard roof breaks and enhances the cracks of the Forced roof cutting through deep-hole blasting is used to weaken hard roofs without rock layer [9,10]. Limited sure relief to enrich the maintenance effect of the roadway while increasing the gas extracresearch has been conducted on deep-hole blasting to force roof caving for pressure relief tion rate. The transmission of blasting stress waves and the development of cracks explored through numerical analysis and simulation tests of deep-hole blasting.

These revealedthat that blasting stress waves propagated uniformly along the
Partial zoom contours of of effective differenttimes: times:
Similarity Theory Principle
Experimental Model Construction
Result Analysis
Breaking Laws of the Thick and Hard Roof
Mechanism of Pressure Relief and Permeability Enhancement
Test Face Overview
Blast-Hole Spacing
Distance of the End of the Blast-Hole
Pressure Relief Effect after Blasting Roof Cutting
Findings
Conclusions
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