Meitan xuebao (May 2024)
Characteristics and mechanism of rock fracturing caused by high voltage electric pulse rock mass based on electrohydraulic effect
Abstract
High voltage electrical pulse fracturing technology based on electrohydraulic effect is a new type of rock mass fracturing technology. This technique is characterized by its safety, high efficiency, environmental friendliness and controllable energy usage. It holds a significant potential for its application in the stress control of surrounding rock in coal mines because the complex stress conditions present in underground rock mass. To further investigate the cracking effect of the technology on hard rock mass under different surrounding rock stress conditions, the numerical simulation of high voltage electric pulse rock mass cracking was carried out on the rock sample based on the RHT damage constitutive model by LS-DYNA. The processes of damage evolution and effective stress evolution inside the rock mass were collected. The cracking characteristics and crack propagation mechanism of the rock mass were analyzed. The numerical simulation overcomes the problem that it is difficult to effectively monitor the internal rock mass during the cracking process due to the fast discharge process and large electromagnetic interference in the indoor test. The self-developed high-voltage electrical pulse rock fracturing test platform was used to carry out the high voltage electrical pulse rock fracturing test under different surrounding rock stress conditions, and the reliability of the numerical simulation results was verified by the obtained rock surface fracture characteristics. The following conclusions are obtained: ① The numerical model of LS-DYNA high voltage electric pulse rock mass fracturing is established based on the RHT constitutive model. The equivalent parameters for the numerical simulation are derived according to the energy equivalent relationship between explosive blasting and high voltage electric pulse. The reliability of these parameters is confirmed by comparing the laboratory tests results with the numerical simulation results. ② By analyzing the crack propagation on the upper surface of specimens, it reveals that the crack will deflect in the direction of the maximum compressive initial stress. Initially, the total length of the crack first decreases gradually during this process. As the angle between all cracks and the maximum initial compressive stress becomes less than 45°, the total crack length begins to increase gradually. ③ Numerical simulations demonstrate that the dynamic stress resulting from high voltage electric pulse discharge is much greater than the initial stress in the surrounding rock during the early stages of fracturing. Dynamic stress plays a leading role in rock failure in this process. As the dynamic stress quickly diminishes during propagation, the initial surrounding rock stress is gradually close to the dynamic stress and finally dominates the initiation and propagation of cracks. The results indicate that surrounding rock stress plays a crucial role in determining the development and expansion characteristics of rock mass cracks. It notably influences the direction of crack expansion. When the high voltage electric pulse fracturing technology is used to crack the deep rock mass, the stress state of the rock mass should be considered. The scientific fracturing scheme should be formulated to achieve an efficient fracturing of the rock mass. The research results provide a reliable numerical simulation method for high voltage electric pulse rock fracturing and a reference for the formulation of deep rock mass fracturing scheme.
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