A Strain-Based Percolation Model and Triaxial Tests to Investigate the Evolution of Permeability and Critical Dilatancy Behavior of Coal
Modeling the coupled evolution of strain and CH4 seepage under conventional triaxial compression is the key to understanding enhanced permeability in coal. An abrupt transition of gas-stress coupled behavior at the dilatancy boundary is studied by the strain-based percolation model. Based on orthogo...
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MDPI AG
2018-08-01
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| Online Access: | http://www.mdpi.com/2227-9717/6/8/127 |
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doaj-art-f43b50fc08364a169299344f60add00a2018-08-22T08:17:21ZengMDPI AGProcesses2227-97172018-08-016812710.3390/pr6080127pr6080127A Strain-Based Percolation Model and Triaxial Tests to Investigate the Evolution of Permeability and Critical Dilatancy Behavior of CoalDongjie Xue0Jie Zhou1Yintong Liu2Sishuai Zhang3School of Mechanics and Civil Engineering, China University of Mining and Technology, Beijing 100083, ChinaSchool of Mechanics and Civil Engineering, China University of Mining and Technology, Beijing 100083, ChinaSchool of Mechanics and Civil Engineering, China University of Mining and Technology, Beijing 100083, ChinaSchool of Mechanics and Civil Engineering, China University of Mining and Technology, Beijing 100083, ChinaModeling the coupled evolution of strain and CH4 seepage under conventional triaxial compression is the key to understanding enhanced permeability in coal. An abrupt transition of gas-stress coupled behavior at the dilatancy boundary is studied by the strain-based percolation model. Based on orthogonal experiments of triaxial stress with CH4 seepage, a complete stress-strain relationship and the corresponding evolution of volumetric strain and permeability are obtained. At the dilatant boundary of volumetric strain, modeling of stress-dependent permeability is ineffective when considering the effective deviatoric stress influenced by confining pressure and pore pressure. The computed tomography (CT) analysis shows that coal can be a continuous medium of pore-based structure before the dilatant boundary, but a discontinuous medium of fracture-based structure. The multiscale pore structure geometry dominates the mechanical behavior transition and the sudden change in CH4 seepage. By the volume-covering method proposed, the linear relationship between the fractal dimension and porosity indicates that the multiscale network can be a fractal percolation structure. A percolation model of connectivity by the axial strain-permeability relationship is proposed to explain the transition behavior of volumetric strain and CH4 seepage. The volumetric strain on permeability is illustrated by axial strain controlling the trend of transition behavior and radical strain controlling the shift of behavior. A good correlation between the theoretical and experimental results shows that the strain-based percolation model is effective in describing the transition behavior of CH4 seepage in coal.http://www.mdpi.com/2227-9717/6/8/127enhanced permeabilitydeviatoric stressmechanical behavior transitionCH4 seepagevolumetric strainstrain-based percolation model |
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| language |
English |
| format |
Article |
| author |
Dongjie Xue Jie Zhou Yintong Liu Sishuai Zhang |
| spellingShingle |
Dongjie Xue Jie Zhou Yintong Liu Sishuai Zhang A Strain-Based Percolation Model and Triaxial Tests to Investigate the Evolution of Permeability and Critical Dilatancy Behavior of Coal Processes enhanced permeability deviatoric stress mechanical behavior transition CH4 seepage volumetric strain strain-based percolation model |
| author_facet |
Dongjie Xue Jie Zhou Yintong Liu Sishuai Zhang |
| author_sort |
Dongjie Xue |
| title |
A Strain-Based Percolation Model and Triaxial Tests to Investigate the Evolution of Permeability and Critical Dilatancy Behavior of Coal |
| title_short |
A Strain-Based Percolation Model and Triaxial Tests to Investigate the Evolution of Permeability and Critical Dilatancy Behavior of Coal |
| title_full |
A Strain-Based Percolation Model and Triaxial Tests to Investigate the Evolution of Permeability and Critical Dilatancy Behavior of Coal |
| title_fullStr |
A Strain-Based Percolation Model and Triaxial Tests to Investigate the Evolution of Permeability and Critical Dilatancy Behavior of Coal |
| title_full_unstemmed |
A Strain-Based Percolation Model and Triaxial Tests to Investigate the Evolution of Permeability and Critical Dilatancy Behavior of Coal |
| title_sort |
strain-based percolation model and triaxial tests to investigate the evolution of permeability and critical dilatancy behavior of coal |
| publisher |
MDPI AG |
| series |
Processes |
| issn |
2227-9717 |
| publishDate |
2018-08-01 |
| description |
Modeling the coupled evolution of strain and CH4 seepage under conventional triaxial compression is the key to understanding enhanced permeability in coal. An abrupt transition of gas-stress coupled behavior at the dilatancy boundary is studied by the strain-based percolation model. Based on orthogonal experiments of triaxial stress with CH4 seepage, a complete stress-strain relationship and the corresponding evolution of volumetric strain and permeability are obtained. At the dilatant boundary of volumetric strain, modeling of stress-dependent permeability is ineffective when considering the effective deviatoric stress influenced by confining pressure and pore pressure. The computed tomography (CT) analysis shows that coal can be a continuous medium of pore-based structure before the dilatant boundary, but a discontinuous medium of fracture-based structure. The multiscale pore structure geometry dominates the mechanical behavior transition and the sudden change in CH4 seepage. By the volume-covering method proposed, the linear relationship between the fractal dimension and porosity indicates that the multiscale network can be a fractal percolation structure. A percolation model of connectivity by the axial strain-permeability relationship is proposed to explain the transition behavior of volumetric strain and CH4 seepage. The volumetric strain on permeability is illustrated by axial strain controlling the trend of transition behavior and radical strain controlling the shift of behavior. A good correlation between the theoretical and experimental results shows that the strain-based percolation model is effective in describing the transition behavior of CH4 seepage in coal. |
| topic |
enhanced permeability deviatoric stress mechanical behavior transition CH4 seepage volumetric strain strain-based percolation model |
| url |
http://www.mdpi.com/2227-9717/6/8/127 |
| _version_ |
1612677942983262208 |