August 17, 2022
Do You Know High-Pressure Rotary Pile Construction Process?
THE PROCESS OF HIGH-PRESSURE ROTARY PILE CONSTRUCTION
1. Drill positioning. The rotary jetting pile machine is moved to the specified pile position, and the drill bit is aligned to the center of the hole position. At the same time, the drilling rig is leveled, placed smoothly and horizontally, and the vertical deviation of the drill pipe is not greater than 1 % – 1.5 %. Once in place, the first low pressure (0.5MPa) water injection test is to check whether the nozzle is smooth, and the pressure is normal.
2. Prepare cement slurry. When the pile driver is moved, the cement slurry will be mixed according to the ratio determined by the design. Firstly, add water into the barrel, then pour cement and external admixture into it, start the mixer for 10-20 minutes, then unscrew the valve at the bottom of the mixing barrel, put in the first screen(aperture 0.8mm), filter and flow into the slurry pool, then pump in the second filter (aperture 0.8mm) through the slurry pump, filter for the second time and flow into the slurry barrel, standby when pressing the slurry.
3. Drilling(triple tube method). When the geological drilling rig is used, the drill bit is drilled at the predetermined pile position to the design elevation (the pre-drilling aperture is 15 cm).
4. Intubation(single tube method, double tube method). When a rotary jet grouting pipe is used for drilling operation, the two processes of drilling and intubation can be combined. When the first stage penetrates into the soil, it can be penetrated by the injection or vibration of the jet pipe itself. The process is that the drilling rig is started, and the high-pressure slurry pump is opened to transport cement slurry at low pressure so that the drill pipe vibrates along the guide frame and the jet sinks into holes. Until the design elevation of the pile bottom, the observed working current should not be greater than the rated value. After drilling, pull out the drill pipe and insert the rotary nozzle. In the process of intubation, in order to prevent the mud sand from blocking the nozzle, the lower pressure (0.5 ~ 1.0 MPa) can be used to inject water along the lower pipe.
5. Lift the slurry tube, mixing. After the slurry tube sinks to the design depth, stop drilling, rotate without stopping, increase the pressure of the high-pressure mud pump to the construction design value (20-40MPa), and sit on the bottom of the slurry spraying 30s later, while spraying slurry, while rotating, while lifting the drill pipe in strict accordance with the design and test piles to determine the lifting speed. In the case of two-pipe or three-pipe construction, after reaching the design depth, connect the high-pressure water pipe and air pressure pipe, start the high-pressure clear water pump, mud pump, air compressor, and drilling rig for rotation, and control the pressure, flow rate and air volume with instrumentation, and start lifting when the predetermined value is reached, and continue to rotate and lift until the expected reinforcement height is reached and then stop.
6. Partial treatment of pile head. When the nozzle lift is close to the top of the pile, it should start from 1.0m below the top of the pile, slowly lift the rotary jet, rotary jet for several seconds, and then slowly lift 0.5m upward until the top of the pile stop slurry surface.
7. If the gravel stratum is encountered, in order to ensure the pile diameter, the grouting and mixing can be repeated: according to the above 4 ~ 6 steps, the grouting and mixing can be repeated until the grouting pipe is lifted to the stopping surface, the high-pressure slurry pump ( water pump, air compressor ) is closed, the transportation of cement slurry ( water, wind ) is stopped, the rotary grouting pipe is rotated and lifted out of the ground, and the drilling rig is closed.
8. Cleaning. Inject the appropriate amount of water into the slurry tank, open the high-pressure pump, and clean the remaining cement slurry in all pipelines until basically clean. And the soil adhered to the nozzle is cleaned.
9. Displacement. Move the pile machine for the next pile construction.
10. Slurry replenishing. After the completion of the jet grouting operation, due to the water release effect of the slurry, there are generally varying degrees of shrinkage, resulting in concave holes on the top of the consolidation body. It is necessary to use the cement slurry with a water-cement ratio of 1.0 to recharge in time.