Mechanical characteristics and energy dissipation evolution of coal under triaxial unloading

Abstract:

The coal and roadway of isolated island working face are affected by surrounding mining disturbance, and the unloading confining pressure of coal mass shows dynamic failure characteristics under cyclic loading and unloading. In order to explore the mechanical characteristics of coal under different load paths, the conventional triaxial (T), triaxial cyclic load (TC), and corresponding unloading confining pressure (TU, TCU) tests were carried out by TAW-2000 three-axis electro-hydraulic servo rigid testing machine. The strength, deformation, acoustic emission (AE) events, and energy dissipation characteristics of coal under different confining pressures were analyzed. Research on the unloading characteristics of coal in disturbed area was carried out. Results show that the strength of fitting regression under TCU was lower than that under TU, higher than that under TC. Under the stress path of unloading confining pressure (TU, TCU), the AE peak value lagged behind the stress peak value, and the AE ringing counts increased sharply at the failure point of coal sample, which was higher than that under conventional triaxial (T, TC). During the cycle processes (TC, TCU), when the stress level reached 70% of the peak strength, Kaiser effect gradually disappeared and Felicity effect appeared. In the cyclic loading and unloading (TC) test, the relative stress level reached 60%, the damage of coal sample was aggravated, and the proportion of elastic strain energy decreased gradually. The larger the confining pressure was, the smaller the impact energy index was; the order of impact energy index from small to large was: triaxial cyclic load (TC)