综放工作面覆岩破坏特征及裂隙演化相似模拟试验研究

Similar simulation study on failure characteristics and fracture evolution of overlying strata in fully-mechanized caving face

针对煤层开采后常出现矿压显现剧烈、煤岩透气性增大和地表下沉等问题,利用二维相似模拟试验研究综放工作面覆岩破坏特征并通过分形理论表征裂隙演化规律。试验结果表明:煤层基本顶初次来压步距为78 m,周期来压步距为24 m;煤层采动裂隙发育,距煤层顶板超过35 m;煤层开采后形成的覆岩裂隙具有分形特征,其分形维数随工作面的推进总体趋势增大;随着工作面的推进,开采位置与覆岩应力测点的水平距离小于40 m时,最初的原岩应力转变为应力集中,当工作面推过应力测点15~20 m后,应力卸压后会出现最小值,随后趋于稳定值;上覆岩层由下而上的垮落表现为非线性,其下沉形态为非对称性,总体垮落趋势近似呈“凹”型。研究结果进一步解释了采动过程中覆岩破坏及裂隙演化规律,可为煤炭开采顶板管理和煤层气抽采提供参考依据。

Aiming at the severe mine pressure behavior,increased gas permeability of coal and rock,surface subsidence and other problems after the coal mining,the failure characteristics of overlying strata in fully-mechanized caving face were studied by 2D similar simulation experiment,and the evolution laws of fracture were characterized by using the fractal theory.The results showed that the first weighting step distance at the basic top of coal seam was 78 m,and the periodic weighting step distance was 24 m.The mining-induced fracture of coal seam developed with the distance of more than 35 m to the coal seam roof.The fractures of overlying strata formed after the coal mining had the fractal characteristics,and the fractal dimension increased with the advancement overall trend of working face.With the advancement of working face,when the horizontal distance between mining location and measurement point of overlying strata stress was less than 40 m,the original native rock stress converted into the stress concentration,and when the working face passed the stress measuring point for 15~20 m,the stress after the pressure relief would appear the minimum value and then tended to be stable.The collapse of overlying strata from bottom to top was nonlinear,and its subsidence form was asymmetric,while the overall collapse trend was approximately“concave”type.The research results further explain the overlying strata failure and fracture evolution laws in the mining process,and provide reference basis for the roof management and coalbed methane extraction in coal mining.