煤矿地下水库坝基层间岩体破坏及突渗力学模型

Failure analysis of rock strata between upper and lower coals under underground reservoir in coal mine and its critical percolation model of jumping permeability

煤矿地下水库技术为西部矿区矿井水资源储存和利用提供了新的途径。煤矿地下水库安全稳定的科学问题之一是开采扰动下煤岩体渗透特性突变机理及量化表征。以陕西大柳塔煤矿为原型开展了煤矿地下水库层间岩体裂隙演化的物理相似模拟试验和三轴循环加卸载渗流耦合试验。结果表明:下煤层工作面朝上部水库推进过程中层间岩层发生拉伸剪切破坏,裂隙逐渐向水库坝体方向延伸,采用数字散斑方法观测到坝基岩体裂隙网络由离散局部变形连通形成宏观裂缝,并贯穿至煤柱坝体;从几何和拓扑角度定量地分析了裂隙网络的幂律分布特征,证实了裂隙演化在空间上存在连通概率,岩层的裂隙网络连通属于渐进式,区别于岩石试件裂隙激增式扩展过程。综合考虑原岩应力、初始采动应力、循环加卸载等作用,发现采动应力导致煤体的体胀作用远大于砂岩,砂岩作为硬岩关键层有利于抑制裂隙扩展和渗透增加;采用基于分数阶理论的非达西渗透率公式计算瞬态法测试的渗透率,相比常规计算方法具有更好的灵敏性,渗透率突变伴随着应力突降、体应变激增、破裂信号陡增等行为,揭示了渗透率的本质是裂隙网络的拓扑连接,提出了突渗的力学定义和拓扑定义。采用逾渗理论将裂隙网络连通视为连续相至非连续相的跳跃行为,建立了煤岩体突渗的逾渗模型,经应力渗流、蠕变渗流等试验验证模型有效且形式简单,为突渗力学行为的数学描述奠定了基础。

The underground reservoir technology for water resources storage and recycling has provided a new way in the mining areas of western China.one of the scientific issues for the safety and stability of underground reservoirs in a coal mine is the mechanism and quantitative characterization of sudden changes in the permeability characteristics of coal and rock under mining disturbance.Taking the underground reservoirs in the Daliuta coal mine as an example,this study carried out a two-dimensional physical similarity model test of the fracture evolution of rock stratum between upper and lower coals,and the triaxial cyclic loading and unloading seepage coupling tests.In the process of the working face of the lower coal seam advancing towards the upper reservoir,the tensile and shear failure occurred in the middle stratum,and the cracks gradually extended to the direction of the reservoir dam.Using the digital image correlation method,it was observed that the fracture network of the rock mass as the dam foundation was connected from discrete local deformation to macro cracks,which penetrated into the coal pillar dam.The power-law distribution characteristics of mining fracture networks were quantitatively analyzed from the perspective of geometry and topology,and it was confirmed that the fracture evolution has connectivity probability in space.The connection of fracture network of rock strata between upper and lower coals under an underground reservoir is gradual,which is different from the rapid expansion process of fracture in rock samples.The volume expansion of coal caused by mining stress is much greater than that of sandstone under the combined effects of in-situ stress,initial mining stress,cyclic loading,and unloading.As a key stratum of hard rock,sandstone is conducive to inhibiting fracture expansion and permeability increase.The permeability measured by a transient method was calculated by the non-Darcy permeability formula based on the fractional calculus theory,which has better sensitivity than the conventional calculation method.The permeability upheaval of rock often coincides with the behaviors of the sudden drop of stress,the expansion of volume strain,and the sudden increase of fracture signal.It was further revealed that the essence of permeability is the topological connection of the fracture networks,and the mechanical and topological definitions of permeability upheaval were put forward.Based on the percolation theory,the connectivity of the fracture networks is regarded as the jumping behavior from the continuous phase to the discontinuous phase,and the percolation model of jumping permeability in coal and rock mass was established.It was verified by stress-seepage tests and creep-seepage tests that the model is effective and simple,which lays a foundation for the mathematical description of the mechanical behavior in permeability upheaval.