循环载荷作用下含水煤岩组合体损伤特性及裂纹扩展规律

Damage Characteristics and Crack Expansion Law of Water-Bearing Coal-Rock Composite Under Cyclic Loading

同忻煤矿8105工作面煤岩体和隔水煤柱长期受水化作用影响,受矿震、采动应力等循环载荷扰动明显,现以该工作面为研究背景,在实验室开展了不同含水率下3种不同顶底板岩性(泥岩、砂岩、石灰岩)的煤岩组合体单轴压缩及循环加卸载试验。通过力学试验分析获得了其损伤劣化机制和能量演化规律,并基于电镜扫描、数字散斑和RFPA数值模拟,揭示了其裂纹从微观到宏观的破坏规律。结果表明:(1)随着含水率增大,煤岩组合体试件的峰值强度劣化幅度逐渐降低,4个阶段饱水百分比的试件峰值轴向应变逐渐减小,循环加卸载条件下要比单轴压缩条件下阶段劣化幅度更大,阶段劣化度由大到小依次为:N20、S20、SH20;(2)水化作用下,煤岩体结构面胶结程度降低,由致密变得软弱,循环加卸载情况下,随岩煤强度比增大组合体破坏模式由张拉-劈裂破坏逐渐向拉伸-剪切混合破坏转变;(3)基于RFPA模拟分析得出,循环加卸载下,随着顶底板岩性强度增大,组合体破裂形成的主裂隙逐渐明显,衍生的次生裂隙逐渐变少,水化作用下强度更高的煤岩组合体破坏时仍能保持更强的脆性破坏。该研究成果可为富水工作面的安全生产提供一定的参考借鉴。

The coal-rock mass and waterproof coal column of the 8105 working face in Tongxin Coal Mine have been subjected to hydration for a long time,and the cyclic load disturbance such as mine earthquake and mining stress is obvious.Taking this working face as the research background,the uniaxial and cyclic loading and unloading tests of three different roof and floor lithology(mudstone,sandstone and limestone)under different moisture contents were carried out in the laboratory.The damage deterioration mechanism and energy evolution law were obtained through mechanical test analysis,and the damage law of cracks from microscopic to macroscopic was revealed based on electron microscopy scanning,digital speckle and RFPA numerical simulation.The results are concluded as follows.Firstly,with the increase of moisture content,the peak strength deterioration amplitude of the coal-rock composite specimens gradually decreases,the peak axial strain of the specimens with the water saturation percentage in the four stages gradually decreases,and the stage deterioration amplitude is greater under cyclic loading and unloading conditions than under the single-axis compression condition.The stage degradation degree from large to small is:N20,S20,SH20.Secondly,under the action of hydration,the degree of cementation in the structural surface of the coal-rock mass decreases,and it becomes weak from dense.Under the condition of cyclic loading and unloading,the failure mode of the composite gradually changes from tension-splitting failure to tensile-shear mixed failure with the increase of rock-coal strength ratio.Thirdly,based on RFPA simulation analysis,with the increase of lithological strength of the roof and floor under cyclic loading and unloading,the main fractures formed by the rupture of the composite gradually become obvious,the derivative secondary fractures gradually decrease,and the coal-rock composite with higher strength under hydration can still maintain stronger brittle failure when it fails.The research results can provide certain theoretical guiding significance for the safe production of water-rich working surfaces.