1.School of Energy Science and Engineering, Henan Polytechnic University, Jiaozuo 454000, China;
2.China Institute of Science and Technology, China Three Gorges Corporation, Beijing 100038, China
Abstract:Coal seam water injection is one of the main measures to prevent coal bump in the gateways of fully mechanized caving face. In order to study dynamic mechanical properties and mechanical parameters of water-bearing coal specimens, the uniaxial impact compression tests of cylindrical coal specimens with different moisture contents were carried out by using the Hopkinson pressure bar (SHPB) test system. The effects of moisture contents and impact velocities on the dynamic stress-strain curves, dynamic mechanical parameters, and dissipation energies of coal specimens were studied. (1) Dynamic mechanical parameters of coal specimens are related with their impact velocities and moisture contents. When the moisture contents of coal specimens are a constant, the dynamic compressive strength and dynamic elastic modulus of coal specimens are positively correlated with the impact velocities. When the impact velocities are a constant, the dynamic compressive strength and dynamic elastic modulus of coal specimens are negatively correlated with their moisture contents. (2) The damage dissipation energies of coal specimens during impact directly reflects their degree of micro-fracture development. With the increase of impact time, the damage dissipation energies of coal specimens increase, and the damage dissipation energies reach the maximum when the coal specimens collapses. When the moisture contents are a constant, the failure dissipation energies of coal specimens are positively correlated with the impact velocities; When the impact velocities are a constant, failure dissipation energies of the coal specimens are negatively correlated with their moisture contents. (3) The ratio of damage dissipation energy to failure dissipation energy of coal specimen is defined as its damage factor. Based on the uniaxial impact compression tests results of coal specimens, their damage-viscoelastic constitutive model and constitutive relation were established. The dynamic stress-strain experimental curves of coal specimens with different moisture contents were theoretically fitted. The fitting degree between the theoretical and the experimental curves was higher, so the theoretical curves can be used to represent the stress-strain relationship of uniaxial impact compression coal specimens. The conclusions provide a theoretical basis for the prevention of rockburst by coal seam water injection into deep-holes in coal bump mines.
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