Meso-mechanical properties evolution during fracture of coal cubes under loading

Sample cubes from 4 typical types of coal were tested under uniaxial compression with an electronic univer- sal testing machine. The images of their surface structure evolution were recorded by a high-speed camera. The fracture characteristics and meso-mechanical properties evolution of coal cubes under uniaxial compression was investigated. It is shown that coal cubes present an integrated collapse mode predominated by cleavage along major axial fissures. Me- chanical properties shown diversities for cubes of the same coal type,which is resulted from the inhomogeneity of the internal gaps and fissures. It is also varied with different coal types,affected by inherent factors,such as composition, pore structure,pore size distribution and coal grades. Relationship with mechanical properties of coal cubes during compression was obvious for micrometer-scale fissures with their pore diameter and concentration. Elasticity modulus and strength of compression reduced with the increase of porosity,fissures diameter and fraction. The length of the ini- tial consolidation stage in the strain-stress curve was affected by porosity and directions of coal seam and loading while the peak fluctuation was related to the coalescence of the internal cracks.