Experimental study of coal deformation and permeability characteristics of gas under variable axial compressive loadings

To explore the deformation and gas seepage rules of coal and rock under variable axial compression loadings, with coal pulverized coal specimen pressed for the study, using triaxial stress thermal-hydro-mechanical coal containing gas permeability system, five kinds of coal in different axial compressive loading paths under three axial compressions and gas seepage test were carried out. The results show that: Deformation of coal body can be divided into four stages: compaction, stable development, non stable fracture development and fracture. Strain rate of change of the specimen compaction stage mainly related to open structure surface and the fracture and regardless of the axial compressive load range; the stable development stage, while the axial compression loading rate is different, but in the axial compression loading the same interval, variation of axial strain rate is basically the same. The coal permeability and axial compression loading rate is negatively correlated with changes during the variable axial compression loading early stage and the permeability variation rate and axial compressive loading rate and little correlation in the late period. The above conclusions have important significance to guide the monitoring and early warning of rockburst and coal and gas outburst.