分级加-卸载条件下原煤的渗透及能耗特征研究

Experimental research on energy dissipation and seepage properties of coal under loading-unloading conditions at different stress levels

利用自主研制的含瓦斯煤热-流-固耦合三轴伺服渗流试验装置,进行了含瓦斯原煤分级加-卸载试验,分析探讨了煤岩的变形、渗透特性及能耗特征,结合能耗特征建立了损伤变量方程。研究结果表明:随分级加-卸载进行,煤样的累积残余变形逐渐增加,相对残余变形先降低,后出现残余变形稳定区,临近煤样破坏又上升。随分级加-卸载进行,渗透率总体变化趋势呈螺旋状先降低,后上升,破坏瞬间急剧增大;定义渗透率绝对恢复率η_j和渗透率相对恢复率η_x定量分析了加-卸载渗透率的变化情况,发现η_j先减小,临近破坏又增大,η_x逐渐增大,其中弹性段ηx保持在85%~95%,临近破坏超过100%。随分级加-卸载进行,煤体累积耗散能呈指数函数增加,单级循环耗散能增加。随着轴向应力的增加,主应力差增加,损伤变量值增大,且煤样破坏时的损伤变量临界值Dc≈0.9。

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 ηj and ηx to quantitatively analyse the changes of permeability in loading and unloading processes, respectively. It is found that ηj decreases firstly, and then increases at the critical moment of destruction. However, ηx increases steadily during the process, where ηx maintains at 85%-95% in the elastic stage, and ηx 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.