Study on mechanical properties and damage model of gas?bearing coal under stepped cyclic loading

摘要

Triaxial cyclic loading tests were conducted to examine the damage and failure of gas-bearing coal under stepped cyclic loading by considering the frequency and amplitude of the cyclic load. The stress-strain curves were obtained, and the effects of load frequency and amplitude on parameters such as strength, dynamic tangent modulus, and acoustic emission characteristics were analyzed. The stress-strain curve exhibits stepped hysteresis loops, which can be divided into the compaction stage, the linear elastic stage, and the yield failure stage. As the frequency of cyclic loading increases from 2 to 5 Hz, the strength of gas-bearing coal increases from 32.55 to 40.36 MPa, the maximum dynamic tangent modulus and peak AE counts increase, while the cumulative AE counts decrease. When the amplitude of cyclic loading is increased from 2 to 5 MPa, the strength of gas-bearing coal decreases from 37.94 to 31 MPa, which has negligible effect on the maximum dynamic tangent modulus. The cumulative AE counts increase and the maximum AE counts decrease. Finally, through theoretical derivation and fitting of experimental results, a constitutive model for coal damage and deterioration under the combined effects of gas adsorption and stepped cyclic loading was established. This study provides an important reference for the reasonable selection of mining parameters for gas-bearing coal mines.