Cast-in-place piles are made by directly forming holes in the pile position, then placing steel cages in the holes and pouring concrete. The cast-in-place pile can adapt to various strata, has no pile connection, no vibration, soil squeezing and low noise during construction, and is suitable for use in densely built areas.
Advantages of rotary bored pile construction;
1, rotary drilling rig has the characteristics of low noise, small vibration, large torque and fast hole-forming speed. According to the comparison of impact bored piles in 1 1# building (hotel) project, it takes 2 ~ 3 days for the latter to complete a pile on average, and the noise and vibration of the impact hammer when it hits the rock stratum during pore-forming, while the former only completes a pile. There is no other noise and vibration except the dynamic noise of the pile driver itself when the hole is formed.
2. The rotary pile driver has its own power device, so there is no need to lay cables like other pile drivers. The cables are run over by passing vehicles or there are potential safety hazards such as electric leakage and tripping.
3. Unlike impact drilling, rotary drilling has mud circulation. The excavated soil is basically semi-dry except for some muddy soil in the red clay layer and sand egg layer, which will not cause mud overflow in the site and the soil can be transported out of the site in time.
Construction technology of rotary drilling cast-in-place pile;
1, construction process flow chart of rotary bored pile.
2. Rig is installed in place: the ground tolerance should be no less than 100kPa, and the track shoe should be flat with a slope of no more than 3, so as to avoid power loss and inclined displacement caused by uneven site, and the high center of gravity may easily cause safety accidents.
3. Pile binding: After the pile position is determined, two mutually perpendicular straight lines intersect at the pile point, determine the crossing control points, and mark and protect them.
4. Alignment of pile position: firstly, adjust the mast of rotary drilling rig to make it vertical, and align the drill bucket or auger bit with the pile position.
5. Burying the liners: After the cross control piles are determined, drill holes with a drilling rig to take soil, drill to the designed depth, and bury the liners. The gasket shall be made of steel plate with a thickness greater than 65,438+00 mm, and the diameter of the gasket shall be about 200mm larger than the aperture. The length of liner should be reasonably selected according to the formation conditions. The top of the casing should be about 200 mm above the ground, and the surrounding area should be buried and compacted with clay. The bottom of the pile casing should be located on a stable soil layer, and the center deviation should not be greater than 50 mm Measure the hole depth leveling point, use a level to lead the elevation to the top of the pile casing, and make records.
6. Mud production: Mud mixer is used for production. It is suggested to add water and calculate the volume first, and then add the specified bentonite under stirring. Soda soda is slowly added in the form of solution under stirring, and the stirring time is generally not less than 3min. When necessary, other additives such as viscosity reducer and barite powder can be added to increase the specific gravity of mud and prevent mud leakage.
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