Abstract
The karst collapse pillar (KCP) is a common geological structure in the coal mines of northern China. KCPs contain many fractured coal rocks, which can easily migrate under the action of high-pressure water. The destruction or instability of the cementation structure between the rocks can directly induce coalmine water-inrush accidents. To study the seepage stability of cemented and fractured coal rock under triaxial pressures, a self-designed triaxial seepage testing system was used and the permeability k and non-Darcy factor β of the cemented and fractured coal rock were tested. Furthermore, the 1D non-Darcy seepage equations were used to calculate the evolution criteria of the seepage loss stability. The results show the following: (1) The cemented structure in the KCP under the triaxial pressures can be easily destroyed. The damaged coal and rock body mainly exists in bulk form, and the permeability depends mainly on the effective stress of the particles. (2) The seepage process in the KCP structure is a combination of pore flow, fracture flow, and pipe flow, and the transition of the seepage state is closely related to the change in the magnitude of β. (3) Under the long-term effect of confined underground water, the migration of small fractured particles in the KCP will increase the structural porosity. If the parameter βk2 reaches the threshold value, the seepage system will evolve into a pipeline flow state, eventually causing a water-inrush accident.
Highlights
Erefore, we carried out triaxial seepage tests to investigate the seepage state in karst collapse pillar (KCP), analyzed the seepage characteristics, and developed a new method for estimating seepage loss stability
Based on the above research, we used the Talbot theory to create cemented and fractured coal samples with different grading structures, and considering the influence of multilevel stress on the pore structure of coal, we used a triaxial permeameter to conduct steady-state tests of cemented fractured coal samples. e seepage test explores the effects of the cementation, gradation structure, and effective stress on the seepage stability of the fractured coal rock, and our analysis provides an important theoretical basis for the prediction and early warning of coalmine water-inrush accidents
Effective stress is the fundamental factor leading to particle deformation of fractured coal rock. e principle is to simplify the macroscopic threedimensional force of coal rock, which is equivalent to the effective stress of coal-rock matrix, so as to simplify the complex stress conditions. erefore, the effective stress can better reflect the stress of the cemented and fractured coal rock under the triaxial stress. e effective stress reflects the stress of the cemented fractured coal rock under triaxial stress
Summary
Erefore, we carried out triaxial seepage tests to investigate the seepage state in KCPs, analyzed the seepage characteristics, and developed a new method for estimating seepage loss stability. Considering the gradation structure, the influence of cementation on the seepage stability is not negligible. Based on the above research, we used the Talbot theory to create cemented and fractured coal samples with different grading structures, and considering the influence of multilevel stress on the pore structure of coal, we used a triaxial permeameter to conduct steady-state tests of cemented fractured coal samples. E seepage test explores the effects of the cementation, gradation structure, and effective stress on the seepage stability of the fractured coal rock, and our analysis provides an important theoretical basis for the prediction and early warning of coalmine water-inrush accidents Based on the above research, we used the Talbot theory to create cemented and fractured coal samples with different grading structures, and considering the influence of multilevel stress on the pore structure of coal, we used a triaxial permeameter to conduct steady-state tests of cemented fractured coal samples. e seepage test explores the effects of the cementation, gradation structure, and effective stress on the seepage stability of the fractured coal rock, and our analysis provides an important theoretical basis for the prediction and early warning of coalmine water-inrush accidents
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