Damage Characteristics and Crack Expansion Law of Water-Bearing Coal-Rock Composite Under Cyclic Loading
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.
Coal-rock compositeCyclic loading and unloadingDamage characteristicsCrack expansionDigital speckleNumerical simulation
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