Abstract
When mining extra-thick coal seams, the main cause of strong ground pressure are the high-level thick and hard strata, but as yet there is no active and effective control technology. This paper proposes the method of subjecting hard roofs to ground fracturing, and physical simulation is used to study the control effect of ground fracturing on the strata structure and energy release. The results show that ground fracturing changes the structural characteristics of the strata and reduces the energy release intensity and the spatial extent of overburden movement, thereby exerting significant control on the ground pressure. The Datong mining area in China is selected as the engineering background. An engineering test was conducted on site by ground horizontal well fracturing, and a 20-m-thick hard rock layer located 110 m vertically above the coal seam was targeted as the fracturing layer. On-site microseismic monitoring shows that the crack propagation length is up to 216 m and the height is up to 50 m. On-site mine pressure monitoring shows that (1) the roadway deformation is reduced to 100 mm, (2) the periodic weighting characteristics of the hydraulic supports are not obvious, and (3) the ground pressure in the working face is controlled significantly, thereby showing that the ground fracturing is successful. Ground fracturing changed the breaking characteristics of the high-level hard strata, thereby helping to ameliorate the stress concentration in the stope and providing an effective control approach for hard rock.
Highlights
The main coal seams for high-efficiency mining are thick and extra-thick ones, for which caving mining is mainly used at present
This paper proposes the method of subjecting hard roofs to ground fracturing, and physical simulation is used to study the control effect of ground fracturing on the strata structure and energy release
The results show that ground fracturing changes the structural characteristics of the strata and reduces the energy release intensity and the spatial extent of overburden movement, thereby exerting significant control on the ground pressure
Summary
The main coal seams for high-efficiency mining are thick and extra-thick ones, for which caving mining is mainly used at present. Ju and Xu (2013) analyzed the structural characteristics of overlying hard strata and the ground pressure in a stope following the mining of a 7-m-thick coal seam. The above studies showed that when mining an extrathick coal seam, if the overburden deposits hard roofs, the large suspended area of those hard roofs is the main factor causing strong ground pressure in the working face. Physical similarity simulation is a research method that can accurately and intuitively reflect the overburden structural characteristics (Yan et al 2018) In the study, this method is used to conduct an in-depth investigation of the characteristics of the overburden displacement and strata breaking strength of high-level roofs after GF to reveal the weakening mechanism of GF. A field-application verification is conducted to improve the technical system for subjecting a high-level hard roof to GF
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