流固耦合作用下不同岩性岩石渗透率演化规律试验研究

Experimental research on the permeability evolution of different rock types under fluid-solid coupling conditions

  • 摘要: 煤矿采掘过程中巷道围岩应力场的动态变化导致裂隙发育,覆岩隔水层遭受采动损害,使得上部含水层中的水进入采矿空间,引起矿井涌(突)水灾害风险,因此研究流固耦合条件下裂隙承压岩石的渗透率演化规律具有重要的理论和实际意义。针对神南矿区煤层顶板岩层在开采扰动下的渗透率演化规律,对顶板典型风化基岩、砂岩及火烧区烧变岩试样开展了流固耦合条件下三轴压缩及渗透测试,并结合声发射监测结果,系统分析了不同岩性试样力学损伤特征及渗透率演化规律,揭示了流固耦合作用下不同岩性渗透率演化的内在机理。研究结果表明:3种岩性试样的峰值强度和割线弹性模量随围压的不断增大均呈近线性增长,表明围压对岩石强度具有增强作用,对试样径向应变具有约束作用;不同岩性试样的声发射振铃计数和能量存在差异,该特征与试样矿物成分有关,围压对不同岩性试样的声发射振铃计数具有一定影响;3种岩石试样在不同围压下渗透率变化大致可划分为4个主要阶段,各阶段与偏应力−应变曲线不同阶段具有较好的对应关系。引入声发射损伤变量后的变化趋势与渗透率演化基本一致,渗透率升高的起点位于起裂应力附近,表明微裂纹起裂和扩展是控制不同岩性试样渗透率演化的主导因素。研究结果可以为神南矿区煤层保水采煤和矿井防治水提供一定的理论基础。

     

    Abstract: The dynamic change of surrounding rock stress field in the roadway during the coal mining process leads to the development of fractures, resulting in the mining damage of overlying rock aquifer. As a result, the upper aquifer enters the mining space, increasing the risk of water inrush disasters in mines. Therefore, investigating the permeability evolution of fractured confined rocks under fluid-solid coupling conditions is of significant theoretical and practical importance. Focusing on the permeability evolution of the coal seam roof strata in the Shennan Mining Area under mining-induced disturbances, triaxial compression and permeability tests under fluid-solid coupling conditions were carried out on the typical weathered bedrock, sandstone, and burnt rock samples in burning area. Combining the acoustic emission monitoring results, the mechanical damage characteristics and permeability evolution patterns of different rock types were systematically analyzed, revealing the intrinsic mechanisms of permeability evolution under fluid-solid coupling effects. The results indicate that: The peak strength and secant elastic modulus of the three rock types exhibit a near linear growth trend with the increasing confining pressure, suggesting that confining pressure can enhance the rock strength while restricting the radial strain; There are differences between the acoustic emission ringing count and energy of different rock types, which is related to the mineral compositions. The confining pressure exerts a certain influence on the acoustic emission ringing count of different rock types; The permeability evolution of the three rock types under varying confining pressures can be roughly divided into four main stages, which correspond to the different stages of the deviatoric stress-strain curves; The variation trend of the acoustic emission damage variable is generally consistent with the permeability evolution. The node of permeability increase is near the crack initiation stress, indicating that the crack initiation and propagation of cracks are the dominant factors controlling the permeability evolution of different rock types. The experimental results can provide a theoretical basis for coal seam water conservation mining and mine water prevention in Shennan Mining Area.

     

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