Abstract: The borehole diameter of traditional high-pressure jet grouting technique for cut-off wall construction is mostly small due to the equipment limitation.It is difficult to drill in pebble and boulder formations and the drilling, cutting and shotcrete lifting efficiency is low.By improving traditional high-pressure jet drilling equipment, large-bore helical drill was used to assist the drilling of the high-pressure jet grouting cut-off wall, and the high-pressure fluid jet device(pipeline and nozzle)was embedded in the drilling tool, which realized the integrated construction of drilling and jetting.Based on the Luotang Town flood control project in Wan′an County, Jiangxi Province, the cut-off wall construction test with large-bore helical drilling high-pressure jet grouting was carried out, and the wall-forming effect was verified by combining numerical calculation analysis, indoor test and field test.The results showed that under the same formation parameters, hole spacing, hole depth and grouting pressure, larger boreholes and helical drill could obtain better rock breaking efficiency and stratum adaptability compared with the traditional small-bore high-pressure jet.The results of the wall excavation test, core penetration test and high-density electrical detection test show that good wall forming quality can be obtained by using large-bore helical drill high-pressure jet grouting technique.