Investigation of waveguide synergistic rock fragmentation using a three-dimensional electromagnetic-thermal–mechanical coupled model

Abstract

Shield tunneling in hard rock faces challenges such as high cutter wear rates, driving the need for auxiliary rock-breaking methods. Microwave-assisted rock fragmentation has emerged as an effective auxiliary method for shield tunneling in hard rock formations, offering distinct advantages including volumetric heating, high fragmentation efficiency, and environmental friendliness. However, in large-diameter shield tunnels, a single waveguide proves inadequate for achieving the required extensive rock preconditioning coverage. This study presents a novel hard rock preconditioning strategy employing dual dielectric-loaded converging waveguide antennas (DDLCWA) and develops a comprehensive three-dimensional electromagnetic-thermal–mechanical (EM-T-M) coupled model to analyze the preconditioning effects. The results demonstrate that under dual-waveguide operation, the temperature field exhibits three characteristic zones: high-temperature, low-temperature, and transitional regions. Short-duration, low-power irradiation induces only minor temperature increases in the rock mass, generating insufficient thermal stress to cause damage. Conversely, high-power, prolonged irradiation leads to rapid temperature elevation in the rock beneath the waveguides, producing significant thermal stresses. These stresses result in block-type fragmentation patterns within the high-temperature zones and generate non-penetrating fractures in adjacent areas. The fragmentation pattern in the inter-waveguide region shows strong dependence on spacing configuration. Smaller spacings promote distinct block-type fragmentation, while larger spacings produce non-penetrating fractures of varying lengths. The proposed multi-waveguide synergistic strategy effectively expands the microwave-induced damage zone, successfully addressing the limited coverage issue inherent to single-waveguide systems.