Dataset Information

Numerical simulation on fracturing behaviour of hard roofs at different levels during extra-thick coal seam mining.

ABSTRACT: In fully mechanized caving mining of extra-thick coal seams, the movement range of overburden is wide, resulting in the breakage of multilayer hard roofs in overlying large spaces. However, the characteristics, morphology and impact effect of hard roofs at different levels are different and unclear. In this study, a secondary development was used in the numerical simulation software ABAQUS, and the caving of rock strata in the finite-element software was realized. The bearing stress distribution, fracturing morphology and impact energy characteristics of hard roofs at different levels were studied to reflect the action and difference of hard roof failure on the working face; thus, revealing the mechanism of the strong ground pressure in stopes, and providing a theoretical basis for the safe and efficient mining of extra-thick coal seams with hard roofs.

SUBMITTER: Gao R

PROVIDER: S-EPMC7029886 | biostudies-literature | 2020 Jan

REPOSITORIES: biostudies-literature

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Numerical simulation on fracturing behaviour of hard roofs at different levels during extra-thick coal seam mining.

Gao Rui R Huo Bingjie B Xia Hongchun H Meng Xiangbin X

Royal Society open science 20200122 1

In fully mechanized caving mining of extra-thick coal seams, the movement range of overburden is wide, resulting in the breakage of multilayer hard roofs in overlying large spaces. However, the characteristics, morphology and impact effect of hard roofs at different levels are different and unclear. In this study, a secondary development was used in the numerical simulation software ABAQUS, and the caving of rock strata in the finite-element software was realized. The bearing stress distribution ...[more]

PMID: 32218957

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Project description:To solve the hidden danger of high methane and low permeability gas in the coal mining process, potentially affecting the safety production in an orderly way, we propose the use of deep hole blasting technology to improve the permeability of the coal seam gas drainage, increase the quantity and rate of extraction, and reduce methane output. Taking the geological conditions of the 201 working surface of Tingnan Coal Mine as an example, it is calculated that the single drilled fracture crack extension range is 3.11~5.24 m according to the coal seam deep-hole pre-splitting blasting joint mechanism and fracture propagation mechanics model, providing a theoretical basis for choosing the appropriate hole spacing. Using COMSOL simulation software to simulate the effective gas drainage radius of a coal seam from a two-dimensional perspective on a single borehole radial, the least squares fitting method was used to analyze the simulated data, and obtained the effective drilling extraction radius after pre-split blasting in a deep hole that is 3.6 m, which is in accordance with the theoretical calculations. In order to obtain accurate and scientific calculations, Fast lagrangian analysis of continua (FLAC3D) numerical simulation software was used. After simulating the distribution of plastic zone between two blast holes at different intervals from a three-dimensional angle, and evaluating the development of cracks in the blasting hole, the white zone of the blasting space was completely eliminated when the interval between blasting holes was 7 m, and the cracks could be propagated throughout the surroundings. Therefore, a blasting hole spacing of 7 m is optimal. On-site monitoring in the Nanting coal mine showed that the quantity and rate of extraction of the single hole after pre-splitting blasting were 2.36 times and 1.62 times as much as before. By integrating the borehole drainage amount and the optimized calculation equation, it could be concluded that the permeability coefficient of the coal seam after blasting was 7.78 times as much as before. The function of time-variated drilling methane emission was obtained using multivariate statistical regressions based on the on-site monitored borehole methane emission (qt), and the drilling limit after pre-splitting blasting revealed that the limitation of methane extraction volume was 5.27 times as much as before.

Project description:BackgroundBiogenic and biogenic-thermogenic coalbed methane (CBM) are important energy reserves for unconventional natural gas. Thus, to investigate biogenic gas formation mechanisms, a series of fresh coal samples from several representative areas of China were analyzed to detect hydrogen-producing bacteria and methanogens in an in situ coal seam. Complete microbial DNA sequences were extracted from enrichment cultures grown on coal using the Miseq high-throughput sequencing technique to study the diversity of microbial communities. The species present and differences between the dominant hydrogen-producing bacteria and methanogens in the coal seam are then considered based on environmental factors.ResultsSequences in the Archaea domain were classified into four phyla and included members from Euryarchaeota, Thaumarchaeota, Woesearchaeota, and Pacearchaeota. The Bacteria domain included members of the phyla: Firmicutes, Proteobacteria, Bacteroidetes, Actinobacteria, Acidobacteria, Verrucomicrobia, Planctomycetes, Chloroflexi, and Nitrospirae. The hydrogen-producing bacteria was dominated by the genera: Clostridium, Enterobacter, Klebsiella, Citrobacter, and Bacillus; the methanogens included the genera: Methanorix, Methanosarcina, Methanoculleus, Methanobrevibacter, Methanobacterium, Methanofollis, and Methanomassiliicoccus.ConclusionTraces of hydrogen-producing bacteria and methanogens were detected in both biogenic and non-biogenic CBM areas. The diversity and abundance of bacteria in the biogenic CBM areas are relatively higher than in the areas without biogenic CBM. The community structure and distribution characteristics depend on coal rank, trace metal elements, temperature, depth and groundwater dynamic conditions. Biogenic gas was mainly composed of hydrogen and methane, the difference and diversity were caused by microbe-specific fermentation of substrates; as well as by the environmental conditions. This discovery is a significant contribution to extreme microbiology, and thus lays the foundation for research on biogenic CBM.

Dataset Information

Numerical simulation on fracturing behaviour of hard roofs at different levels during extra-thick coal seam mining.

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Numerical simulation on fracturing behaviour of hard roofs at different levels during extra-thick coal seam mining.

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