Stress-fracture-seepage field behavior of coal under different mining layouts

There are essential differences between the mining-induced mechanical behavior and the material behavior of coal,but the significant influences of mining layouts and mining-induced disturbance are not reflected and consid- ered in traditional rock mechanics researches. In deep underground coal and gas simultaneous extraction practices,the stress-fracture-seepage field behavior of coal under different mining layouts are of significant difference,and there is still a lack of scientific and quantitative analysis and expression on the mining-induced mechanical behavior of coal. To investigate the stress-fracture-seepage field behavior of coal under different mining layouts,the mining-induced me- chanical behavior,mining-induced fracture distribution and mining-induced coal permeability change ratio ( MPCR) evolution process of coal have been quantitatively analyzed by conducting mining-influenced coal mechanical experi- ments under three typical mining layouts,i. e. ,non-pillar mining(NM),top-coal caving mining(TCM) and protective coal-seam mining(PCM). The testing results have shown that the different mining layouts lead to various mining-in- duced stress fields,which further induce diverse fracture fields and seepage fields of coal. The peak stress,axial strain and circumferential stain corresponding to peak stress of coal under different mining layouts decrease in the order of NM,TCM and PCM,while,the absolute value of volumetric strain increase in that order. The diameter scale fractal di- mensions,the distance (Lrise ) between the inflection point of the MPCR evolution process and the mining face of typi- cal coal specimens decrease in the order of PCM,NM and TCM. The coal and gas simultaneous extraction can be opti- mized by determining the range and spatial distribution of coal seam MPCR and Lrise .