坚硬顶板垮落步距大、块度大、矿压显现强烈,探究其损伤断裂特性对岩层控制具有重要意义。研究取样自山西省大同市矿区塔山矿工作面砂岩岩层,对试样预制不同角度的裂缝,并根据该矿工作面高强度开采实际工况设计了真三轴循环加卸载试验。之后,应用基于物质点法和应变软化本构模型的数值计算工具,建立了不同切缝角度的平面加载模型。通过模型与试验结果的对比,发现该模型能够实现裂隙砂岩在循环加卸载过程中真实宏观物理裂缝的生成,能够模拟出裂隙砂岩在循环加卸载过程中复杂的物理过程。进行了不同切缝角度和不同围压下的裂隙砂岩循环加卸载损伤演化过程的模拟研究。结果表明:(1)宏观裂缝拓展偏转角会随着切缝角度的增加而增加;(2)不同切缝角度下的砂岩试样在循环加卸载时应力集中区域均由裂缝两端萌发,然后向岩石边缘和对角延伸,延伸方向在应力集中区域;(3)随着循环加卸载的进行,耗散能呈现出增加的趋势,宏观主裂缝的发育和贯通会使得耗散能激增;(4)随着围压和切缝角度的增加,峰值应力和完全破坏时的耗散能均会增加。研究成果可为煤层坚硬顶板控制技术提供理论支撑。
The hard roof exhibits a considerable caving step, large block size, and high mine pressure, making it essential to investigate its damage and fracture characteristics for effective strata control. In this study, sandstone samples were carefully selected from the working face of Tashan Mine in the Datong mining area of Shanxi Province. These samples were deliberately prefabricated with cracks at various angles. A true triaxial cyclic loading and unloading test was then developed to simulate the actual mining conditions at the face of the mine. Subsequently, a numerical calculation tool based on the material point method and a strain softening constitutive model were used to establish a plane loading model incorporating different angles of prefabricated cracks. Comparison between the model calculations and experimental results revealed the capability of the model to accurately replicate the formation of real macroscopic physical cracks in fractured sandstone during cyclic loading and unloading, capturing the complex physical processes involved. Furthermore, a simulation study was conducted to examine the cyclic loading and unloading damage evolution process of fractured sandstone under varying angles of prefabricated cracks and different confining pressures. The findings indicate that: (1) The deflection angle of macroscopic crack propagation increases with the angle of the prefabricated crack. (2) Stress concentration areas in the sandstone samples originate from both ends of the crack during cyclic loading and unloading, extending to the rock's edge and diagonal in the stress concentration region. (3) As cyclic loading and unloading progress, dissipation energy steadily rises, especially with the development and propagation of macroscopic main cracks. Peak stress and dissipation energy at complete failure increase with higher confining pressures and angles of prefabricated cracks. These research finding can provide theoretical support for the control technology of hard roof in coal seams.
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