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Experimental Investigation on Post-Peak Permeability Evolution Law of Saturated Sandstone under Various Cyclic Loading–Unloading and Confining Pressure. WATER 2022. [DOI: 10.3390/w14111773] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The permeability evolution law of saturated rock under cyclic loading–unloading after shear yield is an important basis for revealing the water resistance performance and water inrush risk of overlying rock under multiple mining conditions. In this paper, the influence of the confining pressure, the cyclic loading–unloading times (CLT), and the volumetric strain on the post-peak permeability of saturated sandstone was studied by carrying out a post-peak permeability experiment. Based on SEM images and an improved simulated annealing algorithm, the 3D internal structure characteristics of sandstone samples before and after the experiment were reconstructed. The influences of the confining pressure on pore diameter, effective porosity, connectivity, seepage path length, and tortuosity of the sandstone before and after the experiment are discussed. Research results indicated that (1) In the post-peak cyclic loading–unloading stage, the volumetric strain is negatively correlated with permeability. At the unloading and initial loading stage, the volumetric strain showed a gradually decreasing trend as the specimen was slowly compressed. However, at the middle and final loading stages, the volumetric strain curve shifted to the left and showed a decreasing trend, resulting in an obvious increase in permeability. (2) The influence of CLT on k is closely related to the confining pressure level. When the confining pressure changed from 4 MPa to 12 MPa, the volumetric strain–average stress hysteretic curve shifted to the left in turn and the corresponding permeability gradually increased. When the confining pressure increased to 16 MPa and 20 MPa, the volumetric strain–average stress hysteretic curve shifted to the right in turn and the corresponding permeability showed a decreasing trend. No matter what the value of CLT, the magnitude of sandstone permeability gradually decreased and the decreasing trend became flat as the confining pressure increased, especially for σ3 = 16 MPa and 20 MPa. (3) No matter what value of the confining pressure, the hysteresis area of the first cycle was larger than that of last three cycles, indicating that the plastic deformation generated in the first cycle was larger than that generated in the last three cycles and the recovery rate of the permeability increased with an increase of CLT. (4) As the confining pressure gradually increased, the pore diameter, effective porosity, and connectivity all approximately showed a linear decrease due to more easily compacted pores and cracks under high confining pressure, lower connectivity, and permeability, while the length and tortuosity of the seepage path increased nonlinearly, roughly due to a more significant shear failure phenomenon where the seepage path became more tortuous, that is, the greater the tortuosity, the longer the seepage path. The research results can provide an important theoretical basis for water resistance performance and water inrush risk assessment of overlying aquifer under the influence of mining stress.
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Fan J, Wang G, Li H, Li X. Studies on Gas Seepage Characteristics in Different Stress Zones of Bottom Coal in Steeply Inclined and Extra-Thick Coal Seams under Mining Action. ACS OMEGA 2021; 6:34250-34262. [PMID: 34963911 PMCID: PMC8697006 DOI: 10.1021/acsomega.1c03500] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/04/2021] [Accepted: 11/29/2021] [Indexed: 05/31/2023]
Abstract
The gas released from the bottom coal of the horizontal slicing mining face in steeply inclined and extra-thick coal seams seriously threatens the safety of the upper slicing mining face. To explore the seepage characteristics of bottom coal gas, the coal deformation and gas permeability evolution law of four coal samples in different stress zones of bottom coal in the working face were analyzed through true triaxial fluid-solid coupling seepage experiments. At the same time, the seepage capacity of bottom coal gas was partitioned according to the field test. The results show the following: (1) The gas permeability of the bottom coal stress concentration zone first decreased and then increased with axial pressure loading and confining pressure unloading. The gas permeability of the bottom coal stress relief zone increased rapidly with decreasing axial pressure and confining pressure. The gas permeability of the bottom coal stress recovery zone gradually decreased with the cyclic loading and unloading of axial pressure and tended to be stabilized. (2) The evolution law of gas permeability in the bottom coal was closely related to the damage and deformation of coal. (3) From the original stress zone to the stress recovery zone, the gas seepage capacity of bottom coal can be divided into four zones, namely, the original seepage zone, the seepage reduction zone, the seepage sharp increase zone, and the seepage reduction zone. The gas seepage capacity in the stress concentration zone was more substantial than that of the stress recovery zone. The results of this study are of great significance for strengthening the dynamic disaster prevention and control of bottom coal gas in the horizontal slicing mining face of steeply inclined and extra-thick coal seams.
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Affiliation(s)
- Jiuyuan Fan
- College
of Safety and Environmental Engineering, Shandong University of Science and Technology, Qingdao 266590, China
| | - Gang Wang
- College
of Safety and Environmental Engineering, Shandong University of Science and Technology, Qingdao 266590, China
- Mine
Disaster Prevention and Control-Ministry of State Key Laboratory Breeding
Base, Shandong University of Science and
Technology, Qingdao 266590, China
| | - Huaixing Li
- College
of Safety and Environmental Engineering, Shandong University of Science and Technology, Qingdao 266590, China
| | - Xinyu Li
- College
of Safety and Environmental Engineering, Shandong University of Science and Technology, Qingdao 266590, China
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Experimental Study on Mechanics and Permeability Properties of Water-Bearing Raw Coal Samples Under In-Situ Stress. APPLIED SCIENCES-BASEL 2019. [DOI: 10.3390/app9122549] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
In this paper, we investigated the mechanical and permeability characteristics ofwater-bearing raw coal samples under in-situ stress, and came to some conclusions, as follows: thepeak strength and peak axial strain of samples gradually decrease with the increase of watercontent. Under the same stress condition, the higher the water content is, the lower the axial strainand radial strain will be. The peak strength and peak strain of the sample both decrease with thewater content as a quadratic function. During the post-peak loading and unloading process, withthe increase of the number of cycles of loading and unloading, the radial strain decrement andincrement of the raw coal sample gradually decrease after loading and unloading confiningpressure. The permeability of samples gradually decreases with the loading confining pressure,and the permeability of the sample gradually increases with the unloading confining pressure. Thepermeability of coal samples increases volatility with the increase of axial strain, and the fittedsample permeability and effective stress are subject to the ExpDec1 function distribution.
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Zhang M, Lin M, Zhu H, Zhou D, Wang L. An experimental study of the damage characteristics of gas-containing coal under the conditions of different loading and unloading rates. J Loss Prev Process Ind 2018. [DOI: 10.1016/j.jlp.2018.07.006] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/28/2022]
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Zhang D, Yang Y, Wang H, Bai X, Ye C, Li S. Experimental study on permeability characteristics of gas-containing raw coal under different stress conditions. ROYAL SOCIETY OPEN SCIENCE 2018; 5:180558. [PMID: 30109103 PMCID: PMC6083660 DOI: 10.1098/rsos.180558] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/06/2018] [Accepted: 05/31/2018] [Indexed: 06/08/2023]
Abstract
The present experimental study on permeability characteristics for raw coal under different stress states is implemented by applying the triaxial self-made 'THM coupled with servo-controlled seepage apparatus for gas-containing coal'; the result indicates that the flow rate of gas in the coal sample gradually decreases with the nonlinear loading of axial pressure and increases with the nonlinear unloading of axial stress and confining pressure. The flow rate, axial stress and confining pressure curves all satisfy the negative exponential function relation. When the sample reaches the peak intensity, the sample will be destroyed and the stress will drop rapidly; then the flow rate of the sample will increase rapidly. At this stage, the flow rate and axial strain show an oblique 'v' pattern. The flow rate of the coal sample increases nonlinearly with the increase of gas pressure; the relation curve between flow rate and gas pressure satisfies the power function relation. Under the same confining pressure and gas pressure conditions, the larger the axial stress, the smaller the flow rate of the coal sample. Under the same axial stress and gas pressure conditions, the flow rate of the coal sample will first decrease, but then increase as the confining pressure decreases. During the post-peak loading and unloading process, the flow rate of the coal sample will decrease with the loading of confining pressure but increase with the unloading of confining pressure, and there will be an increase in wave shape with the increase in axial strain. The flow rate of each loading and unloading confining pressure is higher than that of the previous loading and unloading confining pressure. At the post-peak stage, the relation curve between the flow rate of the coal sample and the confining pressure satisfies the power function relation in the process of loading and unloading confining pressure.
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Affiliation(s)
- Dongming Zhang
- State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400030, People's Republic of China
- College of Resources and Environmental Science, Chongqing University, Chongqing 400030, People's Republic of China
| | - Yushun Yang
- State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400030, People's Republic of China
- College of Resources and Environmental Science, Chongqing University, Chongqing 400030, People's Republic of China
| | - Hao Wang
- State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400030, People's Republic of China
- College of Mathematics and Statistics, Chongqing University, Chongqing 400030, People's Republic of China
| | - Xin Bai
- State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400030, People's Republic of China
- College of Resources and Environmental Science, Chongqing University, Chongqing 400030, People's Republic of China
| | - Chen Ye
- State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400030, People's Republic of China
- College of Resources and Environmental Science, Chongqing University, Chongqing 400030, People's Republic of China
| | - Shujian Li
- State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400030, People's Republic of China
- College of Resources and Environmental Science, Chongqing University, Chongqing 400030, People's Republic of China
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