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循环载荷条件下含瓦斯煤渗透率演化规律分析

Analysis of permeability evolution law of gas-bearing coal under cyclic loading condition

  • 摘要: 为了探究不同循环加卸载条件下含瓦斯煤的渗透演化规律,以原煤煤样为研究对象,利用三轴蠕变−渗流实验系统,设计开展了不同围压和不同循环载荷上限条件下的含瓦斯煤循环加卸载实验,研究了弹性循环加卸载和弹塑性循环加卸载条件下含瓦斯煤渗透特性。研究结果表明:对于不同循环载荷上限下的含瓦斯煤,弹性循环加卸载条件下,随着循环次数的增加,渗透率逐渐减小,绝对渗透率损害率逐渐增大,相对渗透率损害率逐渐减小;弹塑性循环加卸载条件下,渗透特性随着循环次数的增加在不同围压下具有差异性,高围压下含瓦斯煤渗透率依旧随循环进行逐渐减小,低围压下含瓦斯煤渗透率随着循环进行呈减小−增大趋势。高围压条件下含瓦斯煤渗透率损害率与弹性循环加卸载条件下相似,低围压下含瓦斯煤的绝对渗透率损害率先是迅速增大随后趋于平稳,相对渗透率损害率先是迅速下降再趋于平稳。在弹性循环加载条件下,加载阶段和卸载阶段含瓦斯煤的渗透率应力敏感性系数均随着循环次数的增加均单调减小,在弹塑性加载条件下,含瓦斯煤的渗透率应力敏感性系数在一定循环次数内仍呈减小趋势,之后随着循环的增加会产生波动和增加。在加载阶段随着循环进行逐渐减小,卸载阶段渗透率应力敏感性系数逐渐增加,但对于弹塑性循环加卸载条件,含瓦斯煤渗透率应力敏感性系数随着围压的增大而降低。

     

    Abstract: In order to explore the permeability evolution law of gas-bearing coal under different cyclic loading and unloading conditions, raw coal samples were taken as the research object, and cyclic loading-unloading experiments of gas-bearing coal were designed and conducted using a triaxial creep-seepage experimental system under varying confining pressures and cyclic load upper limits. The permeability characteristics of gas-bearing coal under elastic cyclic loading and unloading and elastoplastic cyclic loading and unloading conditions were studied. The results show that for gas-bearing coal under different upper limits of cyclic loading, under the condition of elastic cyclic loading and unloading, the permeability decreases gradually with the increase of cycle times, the absolute permeability damage rate increases gradually, and the relative permeability damage rate decreases gradually; Under the condition of elastic-plastic cyclic loading and unloading, the permeability characteristics are different under different confining pressures with the increase of the number of cycles. Under high confining pressure, the permeability of gas-bearing coal still decreases gradually with the cycle, and under low confining pressure, the permeability of gas-bearing coal decreases with the cycle. The permeability damage rate of gas-bearing coal under high confining pressure is similar to that under elastic cyclic loading and unloading conditions. Under low confining pressure, the absolute permeability damage of gas-bearing coal first increases rapidly and then tends to be stable, and the relative permeability damage first decreases rapidly and then tends to be stable. Under the condition of elastic cyclic loading, the permeability stress sensitivity coefficient of gas-bearing coal in the loading stage and unloading stage decreases monotonously with the increase of the number of cycles. Under the condition of elastic-plastic loading, the permeability stress sensitivity coefficient of gas-bearing coal still shows a decreasing trend within a certain number of cycles, and then fluctuates and increases with the increase of cycles. In the loading stage, the permeability stress sensitivity coefficient decreases gradually with the cycle, and the permeability stress sensitivity coefficient increases gradually in the unloading stage. However, for the elastic-plastic cyclic loading and unloading conditions, the permeability stress sensitivity coefficient of gas-bearing coal decreases with the increase of confining pressure.

     

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