Abstract
To study coal permeability evolution under the influence of mining actions, we conducted a sensitivity index test on permeability to determine the influence of axial and confining stresses on coal permeability. Loading and unloading tests were performed afterward, and the differences between loading and unloading paths in terms of strain and permeability were studied. A permeability evolution model was built in consideration of absorption swelling and effective stress during modeling. An effective stress calculation model was also built using axial and confining stresses. The calculation results of the two models were compared with experimental data. Results showed that permeability were more sensitive to confining stress than axial stress, and effective stress placed a large weight on confining stress. Large axial and radial deformations at peak strength were observed during unloading. In the unloading phase, the permeability of coal began to increase, and the increment was enhanced by large initial axial stress when confining stress was loaded. permeability sensitivity to axial and confining stresses were used to explain these permeability changes. The calculation results of the models fitted the experimental data well. Therefore, the proposed models can be used to calculate effective stress on the basis of axial and confining stresses and describe permeability change in coal under the influence of mining actions.
Highlights
The permeability of coal seams is an important parameter in underground mining and presents many applications (Zhang et al 2017), which include gas drainage system design and ventilation regulation
In the stress concentration region, coal seam is subjected to axial stress from overlying strata, and the roadway and working face around the coal seam provide a certain deformation space that results in the unloading of confining stress
Permeability change with axial stress can be obtained by fixing confining stress and loading axial stress, whereas permeability change with confining stress can be obtained by fixing axial stress and loading confining stress
Summary
The permeability of coal seams is an important parameter in underground mining and presents many applications (Zhang et al 2017), which include gas drainage system design and ventilation regulation. This parameter determines the gas content of underground atmosphere, which presents a potential hazard to mining facilities and personnel. Coal in front of a mining face undergoes original stress, stress concentration, and unloading states successively due to the influence of mining activities (Zhang et al 2017). This process is illustrated, which shows that stress remains constant in the original stress region, whereas it decreases gradually in the stress unloading region.
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