Field and simulation experimental study on the fracturing of hard rock using electromagnetic pulse stress waves

Rockbursts represent a major challenge in the construction of deep hard rock tunnels, where conventional mitigation techniques such as blasting or hydraulic fracturing often result in undesirable crushed zones, limited efficacy in high-strength rock, or uncontrolled crack propagation. This study explores the novel application of electromagnetic pulse stress waves (EPSWs) as a targeted fracturing technique for hard rock, aiming to provide an effective rockburst prevention approach suitable for high-stress and rockburst-prone environments. The primary objective is to evaluate whether EPSWs can serve as a viable and controlled fracturing method for hard rock by examining their fracturing mechanisms, identifying an optimal operational parameter (number of impacts), and quantifying the resulting damage extent. Field tests conducted in the Qinling Water Transfer Tunnel of the Yin Han Ji Wei project demonstrated that EPSWs can efficiently fracture intact hard rock with a uniaxial compressive strength of approximately 123 MPa. Unlike conventional blasting, EPSW-induced cracking develops without forming a crushed zone and exhibits distinct failure characteristics: crack density evolves through three characteristic stages (gradual increase, rapid increase, and stabilization), while crack propagation proceeds in two phases (initial elongation followed by widening). Numerical simulations performed using ANSYS/LS-DYNA, calibrated with field geological parameters, identified an optimal number of three impulse loads—determined through one-way ANOVA of fracture fractal dimensions—resulting in a radial damage extent of about 1.5 m and an axial damage zone of about 0.9 m. Additional impacts did not expand the plastic zone but only accumulated damage within the initially fractured region. The findings confirm that EPSWs represent a viable and controllable technique for hard rock fracturing, offering valuable insights into crack evolution and optimized impact parameters for designing rockburst mitigation strategies in underground engineering.