Abstract
The bed separation backfill grouting (BSBG) is commonly used to mitigate the surface subsidence caused by coal mining. The distribution characteristics of bed separation and its dynamic evolving process are crucial for BSBG design. This paper utilizes the continuum-discontinuum element method (CDEM) to study the distribution characteristics of bed separation for a longwall top coal caving (LTCC) panel of Longquan coal mine. Numerical results indicate that in addition to the bed separation below the primary key stratum, several small bed separations may also occurred in the strata between the primary key stratum and the subordinate key stratum. The bed separations in the overburden could be classified into three classes: the upper bed separation, the middle bed separation, and the lower bed separation. The upper bed separation has the longest duration time, and the middle bed separation has the shortest duration time. And the BSBG should be started before the closure of the middle bed separation. Based on the actual geological information, the BSBG scheme for 4203 LTCC panel is proposed to mitigate the surface subsidence by taken the results of numerical simulation into consideration. In addition, the case study of the BSBG is introduced in detail. By using gangue power slurry, BSBG could not only effectively mitigate the surface subsidence but also solve the problems of environmental pollution and land occupation caused by traditional gangue stacking. The present study could provide technical support for surface subsidence mitigation and coal gangue disposal for LTCC mining with similar conditions.
Highlights
Surface subsidence caused by underground mining is a common environmental problem faced by mining industry worldwide [1,2,3]
The evolution characteristic of bed separation in overburden of an longwall top coal caving (LTCC) panel was studied in detail by utilizing the continuumdiscontinuum element method (CDEM). en, the bed separation backfill grouting (BSBG) scheme for surface subsidence was introduced based on the results of numerical simulation and field verification. e research results could provide reference for subsidence control in similar conditions
E CDEM simulation indicates that the upper bed separation generated earlier than the middle bed separation, and the upper bed separation keeps expanding as the middle bed separation evolves from initiation to closure
Summary
Surface subsidence caused by underground mining is a common environmental problem faced by mining industry worldwide [1,2,3]. The commonly used surface subsidence mitigation techniques in coal mining include pillar and strip mining (PSM), underground goaf backfilling (UGB), and bed separation backfill grouting (BSBG) [2, 5, 8,9,10,11]. The evolution of bed separation in the overburden is a dynamic process, which can be generally divided into four stages: bed separation motivating, opening, expanding, and closing [4, 19] Both laboratory and field tests indicate that the lithology of the overburden, mining depth, working face length, and coal seam thickness are the key factors for the evolution of bed separation [16, 20]. E technology of BSBG, which utilizes surface grouting to backfill the void space of the bed separation through ground boreholes, is an effective method to mitigate the mininginduced land subsidence. The evolution characteristic of bed separation in overburden of an LTCC panel was studied in detail by utilizing the continuumdiscontinuum element method (CDEM). en, the BSBG scheme for surface subsidence was introduced based on the results of numerical simulation and field verification. e research results could provide reference for subsidence control in similar conditions
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