September 13, 2022
Construction Method of Precast Pile
Precast piles include two types precast concrete piles and steel piles. The precast concrete piles commonly used are reinforced concrete solid square piles and prestressed concrete hollow pipe piles. Steel piles include steel pipe piles, H-shaped, and other dissimilar steel piles.
Before the construction of reinforced concrete precast piles, the construction plan should be made according to the design requirements of the construction drawings, the type of piles, the extrusion of soil in the process of pile formation, geological exploration and test piles, and other information. The main contents include: determining the construction method, selecting the piling machinery, determining the piling sequence, pile prefabrication, transportation, and technical and safety measures during the pile sinking process.
1. Construction Method of Hammer-Sunk Piles (Driving-in Method)
Hammer-sinking pile construction method is a piling construction method that uses the impact of the pile hammer falling on the top of the pile to overcome the resistance of the soil to the pile, so that the pile sinks to a predetermined depth or reaches the holding layer. Hammering pile sinking is a standard sinking method for precast concrete piles, which is fast, highly mechanized, and widely applicable, but there is impact noise and vibration to the surface layer during construction, which is limited in urban areas and night construction.
Piling Machinery: piling machinery mainly includes three parts: pile hammer, pile frame, and power unit.
A pile hammer is a machine that exerts an impact force on the pile and pushes the pile into the soil. The common pile hammers in construction are drop hammer, steam hammer ( single-acting steam hammer, double-acting steam hammer ), diesel steam hammer, and hydraulic hammer ( vibrating hammer ).
The pile frame is the equipment that supports the pile body and the pile hammer, guides the direction of the pile and maintains the stability of the pile during the pile driving process, and ensures that the pile hammer impacts along the required direction. It is generally composed of a chassis, guide bar, lifting equipment, spreader bar, etc. According to the length of the pile, the height of the pile hammer, and the construction conditions, the pile frame is selected and the height of the pile frame is determined. Height of pile frame = pile length + height of pile hammer + height of pulley set. The Pile frame is made of steel, and there are tire types, crawler types, rail types, etc. according to the way of moving.
The power device includes power equipment for driving the pile hammer and hoist. Depending on the hammer selected. When using an air hammer, should be equipped with an air compressor; when selecting a steam hammer, it should be equipped with a steam boiler and winch.
(1) Site preparation: remove the ground and underground obstacles, flatten and compact the site, and set up a drainage ditch.
(2) Put the axis, set the pile position, and set the level point (≮2).
(3) Determine the order of piling: soil compaction directly affects the piling progress, construction quality, and surrounding environment.
(4) Connect the water and electricity pipelines on site and prepare the construction equipment; do a good job of pile quality inspection.
(5) Piling test: 2 roots, check whether the process and equipment meet the requirements.
B. Piling Sequence
According to the density of the pile, the piling order is generally divided into three kinds of piles: section by section, from the middle to all sides, and from the middle to both sides.
When the center distance of the pile is not greater than 4 times the diameter or length of the pile, the pile should be driven symmetrically from the middle to both sides, or from the middle to all sides.
When the center distance of the pile is greater than 4 times the edge length or diameter of the pile, the above two methods can be used, or row by row in one direction.
According to the design elevation of the foundation and the specifications of the pile, it is advisable to drive the pile in the order of deep first and then shallow, large first and then small, long first, and then short.
C. Piling Process Sequence:
Set the ruler → Pile in place → Hanging pile in place → Buckle pile cap, drop hammer, take off hook → Low hammer light hit → Formal hit ( pile, pile, static and dynamic load test, pile cap construction ).
Points: using a heavy hammer low hit, start to hit; continuous beating to reduce rebound consolidation; pay attention to the change of penetration, pile driving record ( number, hammer number per meter, pile top elevation, final penetration... ); in case of an abnormal situation ( penetration change; pile suddenly tilt, displacement, rebound; pile serious cracks or pile top broken ), suspension of construction, and the relevant units to study and deal with.
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