Cutting and breaking operations are common in underwater drilling and mining engineering. Because the resistance of the underwater environment is reduced, the gas-assisted water jet method improves the rock-breaking performance of ordinary water jets. However, the rock-breaking mechanism of a gas-liquid two-phase jet in an underwater environment is unclear. Furthermore, the influence of the jet parameters on its rock-breaking performance needs to be studied. Therefore, the fundamental structure of an underwater gas-liquid two-phase jet was analyzed further in this work. On this basis, a rock-breaking orthogonal experiment was conducted. The effects of the water jet system pressure, air flow pressure, transverse velocity, and erosion distance on the rock-breaking performance of underwater gas-liquid two-phase jet were investigated. The essential reasons for the variation in jet erosion performance were discussed. Furthermore, the order of importance and significance of the above four factors on the rock-breaking performance were analyzed, and reasonable jet working parameters were determined. The results show that rock breaking is the result of the joint action of the microjet formed by the water-phase jet impact and gas-phase cavitation collapse. In general, the system pressure has the highest impact on the rock-breaking performance. Therefore, a higher water-jet system pressure should be applied in underwater gas-liquid two-phase jet-breaking operations. The preferred values of the working parameters for the test conditions and selected parameters are as follows: air flow pressure = 0.4 MPa, traverse velocity = 3 m/min, and erosion distance = 10 mm. The research results can provide technical guidance and a reference for underwater cutting and breaking operations.
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