Coal Engineering ›› 2025, Vol. 57 ›› Issue (8): 153-160.doi: 10. 11799/ ce202508021

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Law and micro mechanism of permeability evolution of high-moisture coal samples under cyclic loading and unloading

  

  • Received:2025-03-28 Revised:2025-06-12 Online:2025-08-11 Published:2025-09-11
  • Contact: feng baoDong E-mail:dfb111111@163.com

Abstract:

During coal mining operations, coal pillars are subjected to cyclic loading-unloading, leading to instability and potential water inrush disasters. This process is accompanied by plastic flow, during which the permeability of coal exhibits significant dependence on loading paths. In this study, cyclic loading-unloading permeability tests were conducted on shear-yielded coal samples from Changcheng No.1 Mine under varying confining pressures. The evolution of permeability under full stress-strain and plastic flow conditions was systematically investigated, and the underlying mechanisms were revealed through microstructural analysis. The results indicate that, 1)Permeability evolves in three distinct phases: elastic phase (Permeability decreases due to the closure of primary fractures), elastoplastic phase (Permeability gradually recovers, reaching its maximum at peak stress), and residual flow phase (Permeability declines as axial strain continues to increase); 2) Permeability evolution under cyclic loading exhibits two-phase characteristics: During unloading, permeability increases with decreasing axial strain. During reloading, permeability initially increases and then decreases. At the same axial strain, permeability during unloading is lower than during loading, forming an elliptical hysteresis loop that indicates irreversible damage accumulation; 3) Permeability shows a decreasing trend with increasing confining pressure; 4) Based on 2D SEM images, an optimized simulated annealing algorithm was used to reconstruct 3D pore-fracture models of the samples before and after testing. Characterization of the 3D pore-fracture structure parameters provided microstructural insights into the permeability changes under different confining pressures.

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