Abstract
Fully mechanized top-coal caving mining with high mining height, hard roofs and strong mining pressure are popular in the Shendong mining area, China. The occurrence of dynamic disasters, such as rock burst, coal and gas outburst, mine earthquakes and goaf hurricanes during the coal exploitation process under hard roof conditions, pose a threat to the safe production of mines. In this study, the characteristics of overburden fracture in fully mechanized top-coal caving with a hard roof and high mining height are studied, and the technology of advanced weakening by hard roof staged fracturing was proposed. The results show that the hard roof strata collapse in the form of large “cantilever beams”, and it is easy to release huge impact kinetic energy, forming impact disasters. After the implementation of advanced hydraulic fracturing, the periodic weighting length decreases by 32.16%, and the length of overhang is reasonably and effectively controlled. Ellipsoidal fracture networks in the mining direction of the vertical working face, horizontal fracture networks perpendicular to the direction of the working face, and near-linear fracture planes dominated by vertical fractures were observed, with the accumulated energy greatly reduced. The effectiveness of innovation technology is validated, and stress transfer, dissipation and dynamic roof disasters were effectively controlled.
Highlights
Roof accidents have a high incidence and fatality rate, and are the first of the five major disasters in coal mines, especially in the mining of coal seams under thick hard strata [1,2]
Liu et al [10] proposed a theoretical model of a triangular cantilever beam, built a mechanical model of rock burst and put forward comprehensive measures such as floor deep hole blasting and strengthening support, in view of the rock burst disaster caused by coal seam mining under huge thick and hard magmatic rock bed
Lv et al [11], revealed the precursory characteristics and the mechanism of fault-induced rock burst under the condition of extremely thick hard roofs based on microseismic data and numerical simulation
Summary
Roof accidents have a high incidence and fatality rate, and are the first of the five major disasters in coal mines, especially in the mining of coal seams under thick hard strata [1,2]. The pressure step of a hard roof working face is large and the accumulated elastic energy is released instantaneously, which leads to strong pressure behavior, especially under the condition of large mining height and fully mechanized top-coal mining Accidents such as roof cutting, support crushing, coal wall spalling and roof fall, rock burst were induced, which had a serious threat on the mining safety [6,7]. Yu et al [43] proposed a surface hydraulic fracturing technique to prevent disasters induced by high-level hard strata in underground coal mining, the application of this technology is strictly limited by the location of surface fracturing. Few studies have focused on the impact of dynamic rock bursts and related control technology under the conditions of large span hard roofs and high fully mechanized top-caving mining. The application of the innovation technology was conducted in Burtai mine of the Shendong mining area, the effectiveness of advanced hydraulic fracturing was studied, and a typical hard-top overburden structure model was established
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