ENERGY EVOLUTION MECHANISM IN FAILURE PROCESS OF COALROCK AND ENERGY STRENGTH CRITERION UNDER BIAXIAL LOADING

To investigate coalrock strength and energy evolution mechanism in failure process under biaxial loading，the mechanical parameters were got by testing coalrocks under uniaxial compression，then coalrock mesomechanical parameters were obtained through combining particle flow code with Fish program，conducted the research on coalrock strength and energy evolution mechanism in failure process under biaxial loading was carried out． The results showed that in coalrock failure process under biaxial loading，intermediate principal stress had most significant effect on yield stage，but no effects on post-peak softening stage; coalrocks under biaxial loading basically had not the features of brittle-ductile conversion in post-peak stage; the elastic strain energy was increased firstly and then decreased，its increasing rate reached maximum about one-second of the ultimate strain，the elastic strain energy at post-peak was decreased rapidly at the same rate; the larger the intermediate principal stress was the larger the axial strain that the dissipation energy appeared，but under the larger intermediate principal stress coalrock internal damage once occured and rapidly developed，which would leads to sudden failure of coalrock，while under the smaller intermediate principal stress coalrock failure was a relatively slow process; elastic strain energy limit was a constant and it had no change with intermediate principal stress under biaxial loading，the ratio of elastic strain energy to total energy absorbed and the ratio of dissipation energy to the total energy were also a constant; energy strength criterion derived based on the elastic strain energy limit had clear physical meaning，and comprehensively reflected the influence factors of coalrock failure in essence，which could well express the stresses relationship at coalrock failure under biaxial loading．