Abstract
The effects of confining pressure and pore pressure on the deformation and permeability characteristics of raw coal are studied experimentally. The deformation properties of raw coal by fracture and its permeability evolution laws under the coupling effect of confining pressure and pore pressure were further studied using a tri-axial servo-controlled seepage system for thermo-fluid-solid coupling of methane-bearing coal. The effects of confining pressure and gas pressure on the strength, elastic modulus, and permeability of raw coal were also analyzed. From the results, it was observed that rise in the confining pressure results in reduction of the initial permeability of raw coal and simultaneously increase its strength which results in higher axial deformation upon failure. Rise in gas pressure would increase the permeability and axial strain of raw coal on the whole and reduce its peak strength. Permeability first decreased and then increased during the loading of deviator stress, following a “V-shaped” change pattern. The results of sensitivity analysis indicated that confining pressure more significantly affected the peak strength and elastic modulus than gas pressure, while the gas pressure more significantly affected the permeability of the material than its confining pressure.
Highlights
Underground geotechnical engineering usually faces complex problems of multiphysics coupling, such as the coupling of ground stress field and flow field
Deep strata are located in stress environments mainly characterized by high ground stress, high pore pressure, and complex geological structures, which add to the difficulties of coal mining, and the growing risks of underground dynamic disasters
This study experimentally studied the strength characteristics and seepage laws of raw coal at different confining pressures and gas pressures and quantified the effects of confining pressure and gas pressure on the strength, elastic modulus, and permeability of raw coal through sensitivity analysis
Summary
Underground geotechnical engineering usually faces complex problems of multiphysics coupling, such as the coupling of ground stress field and flow field. To lower the risks of gas disasters, a frequently adopted approach in coal mining is to reduce the gas pressure in coal seams by predraining drilling gas. In this context, the deformation fracture properties and permeability characteristics of coal-rock mass under the coupling effect of confining pressure and pore pressure have emerged as a research hotspot among researchers at home and abroad in recent years [1,2,3,4,5,6,7,8,9]. This study experimentally studied the strength characteristics and seepage laws of raw coal at different confining pressures and gas pressures and quantified the effects of confining pressure and gas pressure on the strength, elastic modulus, and permeability of raw coal through sensitivity analysis
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