Microscopic porous characteristics and permeability of coal rocks of an outburst coal mine

Coal samples are collected from a coal-and gas-outburst mine.The micro-structure and porous 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 electro-hydraulic servo controlled rock mechanics testing system and the numerically controlled transient permeability method.The relationship curves are obtained:principal stress difference vs.axial strain,permeability vs.axial strain,non-Darcy flow β factor vs.axial strain,and acceleration coefficient vs.axial strain.The study shows that the structure of the coal samples is 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 peripheral 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 β and acceleration coefficient have the same change tendency and both are negative.