Abstract: The rock-breaking effect of high-pressure water jet is very important in the rock-breaking technology of high-pressure water jet assisted tunnel boring machine (TBM). In order to improve the efficiency of high-pressure water jet assisted rock-breaking under the working condition of TBM, rock-breaking tests of ultra-high pressure water jet at high linear speed were carried out, and the influences of nozzle moving linear speed, jet pressure and nozzle diameter on the rock-breaking effect were analyzed. The effects of adding abrasive and jet form on the rock-breaking effect were also investigated. The test results show that the cutting depth and cutting width of high-pressure water jet decrease approximately linearly with the increase of nozzle moving linear speed. With the increase of jet pressure, the cutting depth increases approximately linearly, and the pressure is increased from 200 MPa to 280 MPa, the cutting depth is increased by 72%−82%. As the nozzle diameter is increased from 0.35 mm to 0.60 mm, and the cutting depth is increased by 60%−85%. At a high linear speed, the jet flow becomes divergent after adding abrasive. So the cutting depth of adding abrasive is less than that of pure water, and the cutting width of adding abrasive is greater than that of pure water. The cutting depth of sand tube beam is 35%−42% greater than that of long-line jet, and the cutting width of sand tube beam is 78%−85% greater than that of long-line jet. Based on the Crow’s cutting rock theory and regression analysis of test data, a semi-theoretical and semi-empirical prediction model for the cutting depth of ultra-high pressure water jet at high linear speed is obtained, which can provide a reference for the optimization of jet parameters in the rock-breaking technology of high-pressure water jet assisted TBM. The research results are of great significance for improving the efficiency of high-pressure water jet assisted rock-breaking under the working condition of TBM.

Key words: tunnel boring machine, high linear speed, ultra-high pressure water jet, cutting depth, prediction model