4.9　High Pressure Jet Grouting

4.9.1　Before the construction of high pressure jet grouting，the technique grouting test shall be conducted according to the design requirements，and the test quantity shall not be less than 2.

4.9.2　The technical parameters for construction of high pressure jet grouting shall meet the following requirements：

1　The cement grout flow pressure for single-pipe method and double-pipe method should be 20MPa-30MPa，and the airflow pressure for double-pipe method should be 0.6MPa-0.8MPa；

2　The water jet pressure for triple-pipe method should be 20MPa-40MPa；the cement grout flow pressure should be 0.2MPa-1.0MPa and the airflow pressure should be 0.6MPa-0.8MPa；

3　For double high pressure jet grouting the water pressure should be 35MPa±2MPa and flow rate should be 70L/min-80L/min；the grout pressure should be 20MPa±2MPa and flow rate should be 70L/min-80L/min；the compressed air pressure should be 0.5MPa-0.8MPa and flow rate should be 1.0m3/min-3.0m3/min；

4　The lifting rate should be 0.05m/min-0.25m/min and the construction parameters shall be determined according to test pile.

4.9.3　Ordinary Portland cement shall be used for jet grouting.The quantities of admixture and additives shall be determined through tests.The water-cement ratio of cement grout should be taken as 0.8-1.5.

4.9.4　The drilling hole diameter should be 90mm-150mm；the position tolerance of drilling rig shall be less than 20mm；the drilling rig shall be leveled with verticality tolerance of drill pipe less than 1/100.

4.9.5　The distance between drilling rig and high-pressure pump should not be greater than 50m，and the position tolerance of drill hole shall not be greater than 50mm.The jet grouting shall proceed from bottom to top，and the overlap length for successive grouting pipe lifts shall be greater than 100mm.

4.9.6　The repeated jetting measures should be adopted for projects in which large improving area or higher improving strength is required.

4.9.7　Where there are protection requirements for surrounding environment，such measures as quick setting grout，jetting every other hole，recharging slurry，slowing down construction speed or comprehensive high pressure jet grouting technique with mud disposal equipment may be taken.

4.9.8　During construction of high pressure jet grouting，no groundwater pumping shall be conducted in adjacent area under construction influence.