Preface
The level of our residents is rising by the national development and social progress, and the residents’ requirements for the quality of construction in their daily life and work are gradually increasing. In order to meet the most basic living requirements of our residents, the construction department must ensure the stability, comfort and durability of the housing construction.
Therefore, in the process of construction, we should not only supervise and manage the personnel, materials, construction technology, management and design, but also do the basic preparation work before construction, including address survey, foundation establishment and installation of reinforced concrete precast piles and other technical work, so as to fundamentally ensure the quality and performance of housing construction, improve the stability and compressive resistance of housing construction, and lay the foundation for the development of construction industry in China and To improve building construction technology to lay the foundation. In this paper, we focus on the production and application of precast pile technology.
Types of precast piles and their functions
1.Solid concrete square pile
Concrete solid square piles, also known as reinforced concrete solid piles, are square in cross-section, and due to their weight and transportation conditions, precast piles should not exceed 12 meters in the factory, and if they are long, they should be cut short and transported to effectively protect the solid piles from damage. Generally, when using solid concrete square piles, the piles should be sunk by static pressure method and encrypted with tools such as steel mesh at the top of the piles when they are driven in, which can effectively improve the compressive resistance of solid piles.
2.Concrete pipe pile
Concrete pipe piles belong to hollow core piles, and generally centrifugal force is used in the production of concrete pipe piles. Generally, the diameter of pipe pile is different, and the specifications chosen in the use of pipe pile are different due to different roles. Because of the centrifugal force in the production of the pile, it can effectively reduce the excess water in the concrete and make the concrete mechanism more compact, so the concrete pile has high compressive strength, high density and durability. The concrete composition of this pile is high and the corrosion resistance is also strong, so the pile is widely used in various building construction industries.
Preparation for precast pile construction
1.Fabrication of prefabricated piles
Prefabricated piles can be prefabricated at the construction site or made in the factory, depending on the actual needs of the project, in order to facilitate construction and save cost and time. For short length square piles, it is more convenient to be prefabricated in the factory and easy to be transported, and the length is generally within l0m. In addition, pipe piles are generally prefabricated in the factory. Longer square piles are made at the piling site, and square piles and pipe piles are made in the prefabrication plant.
When making, the template has an important guarantee for the quality of the pile, so it is necessary to make sufficient preparation for the pre-setting of the template. Make the pile surface flat and straight, ensure the accurate geometry of the pile. When the side and bottom formwork are produced using the overlapping method, ensure the isolation between the pile surface, no bonding, and paint a good isolation layer. The steel skeleton is usually butt-welded in the process of welding due to the main reinforcement connection, and the steel configuration of the pile tip and pile top is done with special treatment to ensure the construction quality.
2.Transportation of piles
Precast reinforced concrete piles should be set aside for a certain period of time, so that the strength of the pile is in line with the design strength, only after reaching the design strength of the pile can be transported and piling, which is also to fully ensure the quality of the pile, insufficient strength in the process of transportation is easy to damage, and the quality of construction is not guaranteed.
If the piles are lifted in advance, adequate preparations must be made, corresponding treatment measures must be taken, and the piles must be inspected and qualified before transportation. Piles in lifting and handling should pay attention to, to smooth lifting, careful, avoid vibration and impact, lifting point position should be in line with the design provisions, lifting point should be stressed at the same time. In the face of no lifting ring, and in the absence of certain provisions in the engineering design, according to the actual situation of the project, generally according to the location and number of tying points in accordance with the pile length, in line with the principle of minimum lifting moment.
3.Pile stacking
First of all, when stacking precast piles, we should pay attention to the need to ensure the levelness of the stacking site, and lay bedding for stacking, to prevent damage to the precast piles caused by convex terrain, and to prevent the moisture in the land from soaking into the precast piles to produce corrosion and other phenomena, to ensure the quality of precast piles.
Second, pay attention to the surrounding environment when determining the location of the pile, and try to stay away from the construction site to avoid damage to the precast piles caused by the knocking of construction equipment.
Thirdly, pay attention to the classification of precast piles when stacking, and the stacking height should be kept below four layers as far as possible to avoid the precast piles falling down due to the other party being too high, which will not only damage the economic benefits of construction enterprises, but also easily cause harm to the staff.
Pile driving construction technology
1.Piling equipment and selection
(1) Pile hammer
Pile hammer can be used as drop hammer, steam hammer, diesel pile hammer and vibrating hammer. Drop hammer is generally made of cast iron, and there are two kinds of piercing hammer and gantry hammer. It uses rope or wire rope through the hook by the winch along the pile frame guide bar to lift to a certain height, and then free fall to hit the top of the pile; steam hammer is a high-pressure steam or compressed air-powered piling machinery, there are single-action steam hammer and double-action steam hammer two.
(2) Pile frame
Pile frame is to support the pile body and pile hammer, to guide the direction of the pile and maintain the stability of the pile in the process of piling, and to ensure that the pile hammer along the required direction of impact equipment. The pile frame is generally composed of chassis, guiding rod, 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.
(3) Power unit
The power unit of piling machinery is based on the selected pile hammer. When air hammer is used, it should be equipped with air compressor; when steam hammer is selected, it should be equipped with steam boiler and winch.
2.Piling
When the pile driver is in position, the pile frame should be vertical and smooth, and the centerline of the guide bar should be consistent with the piling direction. When the pile starts to be driven, the distance of the hammer should be controlled and a short distance and light blow should be used.
After the pile is stabilized at a certain depth in the soil, the pile will be driven at a specified distance. The principle of pile driving is heavy hammer and low blow, so that the impact of the hammer on the pile head is small and the rebound is small, so that the pile head is not easily damaged and most of the energy is used to overcome the frictional resistance of the pile body and soil and the resistance of the pile tip, so that the pile can be sunk into the soil faster.
3.Piling quality requirements and measurement records
When the final penetration of end-bearing pile is not greater than the design penetration value, the design elevation of pile end can be used for reference; when the elevation of friction pile end reaches the design elevation range, the penetration can be used for reference.
The deviation of the pile position of the driven pile must be in accordance with the relevant quality control regulations. The bearing capacity of the pile is to be checked if it meets the requirements. Piling project is a concealed project, construction should do a good job of each pile observation and records, which is the basis for the acceptance of the project inspection quality.
4.Analysis of common problems in piling construction
(1) serious pile rebound, pile hammer back leap problem
In the selection of pile hammer, if the hammer quality is lighter, it can cause such problems, and the lighter the hammer, the greater the hammer rebound. The lighter the hammer, the greater the hammer kickback. In the process of pressing, if the pile tip encounters a hard obstacle in the stratum that is difficult to overcome, the pile kickback problem will occur.
(2) Pile body is interrupted
The pile body has a large curved convex belly, the pile body is made with insufficient local concrete strength, the pile tip encounters obstacles such as solitary stone or hard soil layer during pile sinking, repeated excessive impact, increasing the drop distance, etc. may cause the pile body to break.
(3) Pile top breaking
When piling, the pile top is directly impacted by the pile hammer, which will produce high local stress. If the concrete protective layer is too thick, the pile top reinforcement mesh is not properly configured, the pile center axis is not perpendicular to the pile top plane, the pile top is not flat and other quality problems will cause the pile top to break.
Pile foundation static compression pile construction technology
Static pile construction technology is a new exploration of pile construction technology, which has been widely promoted and used in the construction of engineering foundations in China, and the quality of engineering construction is strongly guaranteed. This construction process mainly uses the static pressure for construction, this kind of static pressure construction technology has many excellent characteristics, it is vibration-free, noiseless, uniform pile driving into the soil. This construction technique is mainly used in the environment of homogeneous soil and the nature of the foundation is required to be soft.
Its working principle is to use the counterweight and self-weight of the pile press frame, by the pulley, pressurized wire rope, pressure beam, through the winch traction, the entire pile press gravity on the top of the pile, so as to overcome the friction between the foundation soil and the pile body sinking, so as to achieve the purpose of precast pile sinking. In the construction, attention should be paid to the appropriateness of the pressing method. The pile pressing construction generally adopts the construction method of section-by-section extension and section-by-section pressing, which fully ensures the quality of construction.