Coal samples are collected from a coal- and gas-outburst mine. The micro-structural, micro-porous, and micro-fissure characteristics of the samples are observed using scanning electronic microscope. Electro-hydraulic servo tests of four standard coal samples under complete stress-strain process are conducted by using the MTS815.02 rock mechanics testing system and the numerically controlled transient permeability method. Based on the experimental results, the Darcy flow permeability, non-Darcy flow permeability, non-Darcy flow factor beta, and acceleration coefficient are calculated for different strains during the course of destruction of the coal samples. These relationship curves are obtained: principal-stress difference vs. axial strain, permeability vs. axial strain, non-Darcy flow factor beta vs. axial strain, and acceleration coefficient vs. axial.strain. The study shows that the structures of the coal samples are non-homogeneous, consisting mainly of grain-, grid-, and sheet-shaped structures, with some scale-shaped structures and some twisted structures being seen; that because of the action of confining pressure, during the course of destruction of coal samples, the permeability under complete stress-strain process changes as the strain increases, but does not change significantly; and that the non-Darcy flow factor beta and acceleration coefficient have the same change tendency and are both negative.
