Evolution Mechanism and Theoretical Model of Porosity and Permeability in Crushed Coal Under Compression

Abstract

Coal spontaneous combustion is a major threat to coal mine safety. The accumulation of heat from broken coal in goaf is prone to coal spontaneous combustion. A deep study of the evolution mechanism and theoretical model of porosity and permeability in crushed coal under compression is crucial for understanding the process of coal spontaneous combustion. This paper utilizes an experimental apparatus for gas seepage in crushed coal under compression developed by our research team. It systematically explores the changes in strain, porosity, and permeability of single particle and mixed particle coal during stress infiltration. The experimental results show that the strain of coal with different grain sizes has a negative exponential relationship with stress, and porosity and permeability vary inversely and linearly with strain, respectively. Theoretical analysis indicates that the sliding and filling effect of particles is the primary cause of the changes in strain, porosity, and permeability. There is a one-to-one mapping relationship between the total strain, residual porosity, and residual permeability of coal with different grain sizes after compression and their respective change paths. Based on these findings, this paper establishes theoretical relationship models of stress–strain, strain–porosity, and strain–permeability, with total strain, residual porosity, and residual permeability as parameters. These research results will provide theoretical support for a deeper understanding of the occurrence and development processes of coal spontaneous combustion.