Impact of cyclic high-voltage pulse discharge on the formation mechanism of rock plasma channels and quantitative assessment of its weakening effect on rock strength

Abstract

High voltage electric pulse (HVEP) technology is expected to revolutionize deep resource extraction and underground space engineering construction technology. Understanding the establishment mechanism of the plasma channel and the pulsed discharge impact on the mechanical characteristics of rock is considered key to the widespread utilization of this technology. In this work, cycle discharge experiments on sandstone were carried out. Subsequently, the post-experiment rock samples were tested for wave velocity and uniaxial compression tests to quantitatively evaluate the weakening law of the rock's mechanical properties due to cyclic discharge. Concurrently, the formation mechanism of plasma channels within the sandstone was analyzed using Computed Tomography (CT), Scanning Electron Microscopy (SEM) and Energy-Dispersive Spectroscopy (EDS), whereas the weakening mechanism of rock strength by pulsed discharge was discussed. The results demonstrated that the peak current, propagation time of the current in sandstone, and the degree of rock fragmentation increased with the number of cycle discharges. The cycle discharges decreased the P-wave velocity (Vp), uniaxial compressive strength (UCS), and elastic modulus (E) of the rocks. The CT scan results indicated the plasma channel was established in the rock after the first discharge. According to the SEM observations, the existence of intergranular and intragranular cracks in the rock in the plasma channel was revealed, while the rock outside remained undamaged. In addition, the EDS analysis of the plasma channel surface revealed that the cycle discharges formed substances similar to acidic magma, suggesting that the discharge generated high temperatures in the rock. The synergistic action of the high temperature and shock waves leads to the development of plasma channels and the electricfragmentation of rocks. However, the high-temperature effect is limited within the zone of the plasma channels. The research results provide valuable insights into deeply understanding the destruction process of rocks under the application of HVEPs.