A case study of the periodic fracture control of a thick-hard roof based on deep-hole pre-splitting blasting

Baobao Chen,Bing Wang,Changyou Liu

doi:10.1177/01445987211036245

Abstract

A thick-hard roof implies a large hanging-roof and high-frequency dynamic strata behaviour during mining, which may jeopardise personnel safety and equipment. To alleviate these hazards, deep-hole pre-splitting blasting is employed to control periodic fractures in thick-hard roof seams in Datong mining area. Based on loading and instability characteristics, a mechanical model of thick-hard roof periodic collapse is established to investigate the relationships and optimal parameters among the collapse interval, fracturing angle and support working resistance. LS-DYNA was employed to analyse the fracture evolution to determine the optimal charge parameters. The minimum weakening width and average fragmentation of the pre-split roof are obtained. Universal distinct element code simulations were used to determine the thick-hard roof collapse morphology and strata behaviour to confirm the optimal pre-splitting parameters. The deep-hole pre-splitting blasting on-site implementation reduces thick-hard roof collapse intervals, and the supports loading is verified to be safe with sufficient allowance, which show a good control effect on thick-hard roof seams.

Highlights

The presence of a thick-hard roof (THR) in coal mines often causes excessive stress concentration and dynamic strata behaviour
In the Datong mining area, the main mining coal seams belong to Jurassic and Carboniferous formations, which include at least one THR in the near-field that generally falls within the range of the caving zone
The universal distinct element code (UDEC) simulation results revealed that as the working face advanced near the pre-splitting line, the fracturing of the THR controlled by deep-hole pre-splitting blasting (DPB) could collapse in a timely manner with a periodic interval of 8.0 m and properly alleviate the influence of strata behaviour on the working face, according to the morphology change of the THR rotation instability and reduction of the abutment stress peak

Summary

Introduction

The presence of a thick-hard roof (THR) in coal mines often causes excessive stress concentration and dynamic strata behaviour. Keywords Thick-hard roof, collapse characteristics, deep-hole pre-splitting blasting, fracture evolution, controlling effect Based on the THR characteristics of the Xinzhouyao Mine in the Datong mining area (China), the collapse morphology was analysed, and the relationship between fracturing-articulated strata and support resistance was obtained to derive the optimal pre-splitting parameters.

Results

Conclusion