Abstract
Accurate perception of the key stratum instability can improve the safety of coal mining and also provide a basis for alleviating overlying rock strata destruction and environmental disturbance. To efficiently evaluate the instability of the key stratum and its threat to safe mining and environmental protection, the fracture characteristics and weakening mechanisms were studied through physical simulation, theoretical analysis, and field measurement. A scheme and the parameters of confined blasting in water-filled deep hole presplit technology (CBWDHPT) for thick and hard roof (THR) weakening were proposed. Research studies showed that, after the THR fractured into large blocks, the subsequent sliding instability induced serious support-crushing accidents; however, increasing the support strength could only provide limited control. Confined water and infiltrated modified rock mass functioned as the transfer load medium of the explosives, and the CBWDHPT fully utilized high explosion energy to break rocks. Consequently, the collapse and filling of the immediate roof and low-positioned THR, as well as the timely cutting off the middle-positioned THR, could be realized, which alleviated the migration space of THR blocks, overlying strata destruction, and earth-surface step subsidence. Finally, the environmentally friendly strategy (including the CBWDHPT and hydraulic support optimization) for overlying rock strata protection was proposed. In the industrial test, the THR was broken into blocks of different sizes after utilizing the CBWDHPT, and the support working resistance was significantly decreased. It was concluded that the environmentally friendly strategy could effectively reduce the risk of overlying rock strata destruction.
Highlights
IntroductionA series of mining-induced environmental and ecological damages such as groundwater level drop [1, 2], surface subsidence [3], and ecological destruction put forward high requests for the key stratum control
Safety, efficiency, and environmentally friendly are the goals of coal mining
Different strata react distinctly to the mining, and the accurate perception of the fracture, migration, and instability laws of the key stratum was the prerequisite for alleviating the destruction of the overlying rock strata
Summary
A series of mining-induced environmental and ecological damages such as groundwater level drop [1, 2], surface subsidence [3], and ecological destruction put forward high requests for the key stratum control. Different strata react distinctly to the mining, and the accurate perception of the fracture, migration, and instability laws of the key stratum was the prerequisite for alleviating the destruction of the overlying rock strata. Large layer thickness, and good integrity, thick and hard roof (THR), mainly consisting of sandstone and conglomerate, served as the key stratum and formed large overhangs during mining [4]. A strong and hard hanging roof caused high underground stress in underground mines, leading to Advances in Civil Engineering rockburst, coal and gas outburst, and earth-surface step subsidence. THR, especially those in direct contact with coal seams, had a significantly different mining response from that of high-positioned THR, which made their control and safe mining extremely difficult [6, 7]. ese problems could not be solved by increasing the support intensity, creating new challenges for roof control
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