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激波脉动荷载作用下煤岩体动态损伤特征

Dynamic damage characteristics of coal and rock mass under shock wave pulsating load

  • 摘要: 为了研究水中高压电脉冲激波脉动荷载特性及其作用下的煤岩体动态损伤特征,开展了真三轴煤岩体压裂试验。试验研究了不同水压、电压条件下的水激波峰值压力、冲击荷载、加载速率等水激波加载特性,探究了煤岩体钻孔侧壁环向有效应力与动态抗拉强度的关系,同时揭露了煤岩体裂纹起裂应力、扩展角与地应力、水压力、脉冲激波之间的关系。基于CT扫描和ABAQUS数值模拟计算不同液电参数下的煤岩体损伤变量,进而评价煤岩体动态损伤和裂纹起裂扩展形态及演化特征。结果表明:脉冲水激波峰值压力随着放大电压和水压的增加而迅速增加,加载速率随放电电压增加而增加,随水压增加而减小;相对于水压变化,放电电压的变化对水激波峰值压力及其加载速率影响更大;数值模拟与室内试验所得结果吻合度较高,二者从细、微观角度互相印证了随着水压、放电电压的增加,煤岩体的损伤变量增加明显,损伤致裂程度加剧,裂纹数量、扩展长度、开度、复杂程度变化明显,其中放电电压的改变对煤岩体的损伤影响尤其明显。研究结果可以为我国水中高压电脉冲压裂煤岩体,高效抽采煤层气提供指导。

     

    Abstract: To investigate the hydraulic load characteristics of high-voltage electric pulse shock waves in water, as well as the dynamic damage features of coal rock mass subjected to their influence, true triaxial fracturing tests on coal-rock specimens have been carried out. Under varied conditions of water pressure and discharge voltage, the investigation delved into attributes of water shock waves, including peak pressures, impulsive loads, and loading velocities. Elucidating the correlation between the circumferential effective stress at the drill hole periphery and the dynamic tensile strength of coal-rock mass. Furthermore, the study explored the relationships linking the initiation stress and propagation angle of cracks in coal-rock mass with factors such as in-situ stress, water pressure, and electric pulse shocks. Based on CT scans and the ABAQUS numerical simulation software,damage variables for coal rock mass with different hydraulic and electrical parameters were calculate and then evaluate the dynamic damage and crack initiation and propagation morphologies and evolutionary properties of coal rock mass. The results show that the peak pressure of the impulsive water shock increases rapidly with the amplification voltage and the water pressure, and the loading rate increases with the discharge voltage and decreases with the water pressure. Compared to the change in water pressure, the change in discharge voltage has a larger effect on the peak pressure of the water shock and its loading rate. The results of numerical simulations and laboratory tests are in good agreement and confirm each other from a microscopic point of view. The damage variables of the coal rock mass, the degree of damage and cracking significantly increase, and the number of cracks, length of extension, opening, and complexity change significantly with the water pressure and discharge voltage increase. Variations in the discharge voltage have a particularly marked effect on the destruction of coal rock mass. The research results can provide guidance for high electric pulse fracturing coal rock mass in water for efficient extraction of coalbed methane in China.

     

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