Abstract: In this paper, loading-unloading experiments were carried out on gas-contained coal under different stress levels by using self-made thermal-hydro-mechanical (THM) coupling equipment. The characteristics of the deformation, seepage and energy dissipation of coal and rock were analysed, and the damage variable equation was also established by considering the energy dissipation. Research results show that the cumulative residual deformation increases gradually with the advancing of cyclic loading-unloading. The relative residual deformation decreases firstly, then maintains stable at a certain value, and finally rises again when the coal sample is nearly destroyed. With the advancing of cyclic loading-unloading, the overall trend of permeability decreases spirally, and then increases until the coal sample is fractured. Moreover, a sharp increase is observed at the moment of destruction. The absolute recovery rate of permeability and relative recovery rate of permeability are defined as ?j and ?x to quantitatively analyse the changes of permeability in loading and unloading processes, respectively. It is found that ?j decreases firstly, and then increases at the critical moment of destruction. However, ?x increases steadily during the process, where ?x maintains at 85%-95% in the elastic stage, and ?x is more than 100% at the critical moment of destruction. With the advancing of cyclic loading-unloading, the cumulative dissipated energy grows exponentially, and the single-stage cycle of dissipation energy increases. With the increase of the axial stress, the principal stress difference increases, and the value of damage variable also increases. In addition, damage variable of coal Dc is 0.9 when coal is fractured.

Key words: coal containing gas, different level loading-unloading, residual deformation, seepage, energy dissipation