Deformation and acoustic emission behaviors of coal under triaxial compression and pore water pressure

Full stress-strain tests and acoustic emission measurements under uniaxial compression,triaxial compression and pore water pressure were carried out on coal samples with an MTS815.02 rock mechanics test system.It is shown that the triaxial strength and residual strength increase with the increase of confining pressure but reduce with the increase of pore water pressure.In the testing range of low confining pressure,the elastic modulus has great change with confining pressure.Under different testing conditions,the acoustic emission behaviors of coal samples have great differences.Under uniaxial compression test,there are all acoustic emission events at each stage,but under triaxial compression and pore water pressure,the acoustic emission events are smaller before yielding and tend to be active after yielding.The acoustic emission energy of coal samples under uniaxial compression is the largest.With the increase of pore water pressure,the released acoustic emission energy decreases step by step in the process of deformation.