Micro and meso-damage mechanism of coal's strength and deformation characteristics

The properties and morphological structures of three types of coal rocks were experimentally analyzed with MTS815.03 servo-control rock mechanical test system and S250Mk3 scanning electronic microscope.The micro and meso-damage mechanisms of the coal's strength and deformation characteristics were studied with using the theory of damage mechanics.It is shown that the micro and meso-damage variable has great influence on the coal's macroscopic mechanical parameters.The original damage variables of No.3 coal seam in Baodian Colliery and No.3 coal seam in Xuchang Colliery,which both belong to carboniferous-permian Yanzhou Coalfield,decrease by 68.5% and 50.6% compared with No.3 coal seam in Xinhe Colliery,the uniaxial compressive strengths increase by 224.8% and 109.9%,and the elastic moduli increase by 147.3% and 66.9%,respectively.With decreasing damage variable,the uniaxial compression failure gradually changes from plastic to brittle.Macroscopic mechanical properties of the coal rocks are closely related to micro and meso-damage.