High pressure rotary jet pileIt is a kind of high-pressure jet grouting method, which inserts the grouting pipe with a special nozzle into the designed soil depth, and then shoots the cement slurry out of the nozzle in the form of high-pressure flow to impact the cutting soil. Under the action of high pressure jet flow, the soil is destroyed, and the soil particles are spalling off from the soil layer and mixing with cement slurry to form a mixed slurry. Part of the fine particles came out of the ground with the mixed slurry, and the rest of the soil particles were rearranged in a planned way according to a certain proportion and mass of the slurry and soil under the action of the impact force, centrifugal force and gravity of the jet. In this way, the grouting is continuously sprayed from the bottom to the top. After solidification of the mixed slurry, a consolidation body with a certain strength is formed in the soil layer, and the consolidation body is cylindrical.

High pressure rotary jet pileThe basic process types include: single pipe method, double pipe method, triple pipe method and multiple pipe method. The single tube method and double tube method are used more.

The single pipe method is to use the drilling rig to install the special nozzle at the bottom side of the grouting pipe, into the soil layer predetermined depth, with high-pressure mud pump and other devices, to20KPaUnder the pressure of left and right, the cement slurry is ejected from the nozzle to impact the soil to destroy the soil, so that the slurry is mixed with the soil falling from the soil, and after solidification for a certain time, a certain consolidation body is formed in the soil. (The diameter of pile formed by single pipe method is small, which is generally0.3-0.8m)

Double pipe method is the use of double channel double grouting pipe. When the double grouting pipe is drilled to a predetermined depth in the soil layer, a coaxial double nozzle at the bottom side of the pipe will simultaneously eject two kinds of media, high-pressure slurry and air, to impact and destroy the soil. That is to high pressure mud pump and other high pressure generating device ejection20KPaLeft and right slurry, from the inner nozzle in high speed ejection. Under the joint action of high pressure slurry and air flow in the outer ring, the energy of soil destruction increases significantly, and finally a large consolidation body is formed in the soil. (The diameter of pile formed by double pipe method is1.0mOr so)

Triple pipe method: respectively conveying cement slurry and air and high pressure water. In the high-pressure pump and other high-pressure generating device20MPAround the high-pressure water jet stream, around a stream0.7MPaThe left and right cylindric air flow carries on the high-pressure water jet flow and the air flow coaxial jet to cut the soil, forming a large gap, and then the mud pump will inject the pressure2-5MPaWhen the nozzle rotates and lifts, it solidifies into a cylindrical consolidated body with a larger diameter in the soil. (Triple pipe method into the pile diameter is larger, generally in1-2mBut the pile body strength is low, generally in0.9-1.2MPa)

4Key points of construction technology

(1The high pressure equipment and piping system must be checked before rotary spraying, and the pressure and flow meter must meet the design requirements. Before piping, check whether the grouting pipeline is smooth and whether the joint is well sealed.

(2) In the process of intubation, in order to prevent sediment from blocking the nozzle, can be intubated at the water edge.

(3) When the nozzle is inserted into the predetermined depth, the injection operation is carried out from the bottom to the top. When spraying the grouting, it should be noted that the grouting pipe can be lifted until the front of the cement slurry is estimated to have flowed into the nozzle. Personnel on duty must always pay attention to check the initial setting time of slurry, grouting flow rate and other technical parameters, control the speed, speed up. Remove the drill pipe to continue spraying, keep the drill pipe has0.3mThe lap length of shall not make the jet consolidation body disjointed. In the deep rotary spray, the grouting is first sprayed and then rotated and accelerated to prevent the grouting pipe from breaking.

(4) Repeated injection: under the condition of not changing the technical parameters of injection, repeated injection of the same hole can not only increase the effective length of soil damage, so as to increase the diameter or length of the consolidation body and improve the strength of the consolidation body. When all the grouting is re-sprayed, the more times of re-spraying, the better the effect of lengthening the diameter of the consolidation body.

(5) During construction, close cooperation between the front desk and the rear yard for slurry supply should be strengthened. When the rear yard stops supply, the front desk should be informed in time to prevent broken piles and lack of slurry. When the slurry is supplied again, the nozzle should be inserted to the stop point0.5mThe following will be lifted when slurry supply is resumed. If the stop time exceeds3Hours, need to remove the slurry pipe for cleaning.

(6) the cement slurry, water cement ratio shall not be changed at will, to ensure the quality of cement, cement to sieve, its fineness should be in the standard screen allowance is not greater than15%, do not use damp, expired cement.

(7) The distance between the injection grouting hole and the high pressure pump should not be too long to prevent the high pressure hose from being too long and the pressure loss along the way will increase, resulting in the actual injection pressure reduction.

(8) To ensure the construction quality of pile head, rotate the rod to below the elevation1mWhen jet lifting, use slow speed, control in10cm/sOr less.

(9) After the injection, if the slurry surface drops, hydrostatic filling should be carried out immediately in the injection hole until the slurry level is no longer flowing down.

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