With the improvement of urbanization, people's living space develops rapidly to the air and underground. High-rise building has become a symbol of the current city, and its technical management and quality control are particularly critical, among which pile foundation construction is an important factor affecting the quality and safety of high-rise building construction. At present, box foundation, pile foundation and raft foundation are commonly used in high-rise buildings, among which pile foundation is the most common. In the process of pile foundation construction, it is necessary to carry out the whole process control and all-round technical management, do a good job in comprehensive coordination and control management, and correct all possible problems in time.
1 Preparation before pile foundation construction
Precast piles and cast-in-place piles are classified according to construction methods. Usually, precast piles are operated externally. Cast-in-place piles can be drilled, and pile holes can be formed in foundation soil by mechanical drilling, steel pipe extrusion and other methods. Reinforcing cage and cast-in-place concrete are added to the pile. Before the pile foundation construction of high-rise building, site survey must be done well to ensure the smooth progress of pile foundation construction.
1. 1 Investigation of construction site and surrounding environment
Conduct a comprehensive on-site investigation on the pile foundation construction site to provide reliable and true data basis for future work. Clearly distinguish the natural elements such as topography and climate characteristics in the construction site and its vicinity. Master the groundwater quality and water level in the construction area to provide necessary conditions for smooth construction. Clear the depth of foundation pile in the soil layer of the construction site and various related indexes, and understand the specific position, structure and properties of surrounding buildings.
1.2 preparation and construction technology of mechanical equipment
According to the design scheme, reasonable mechanical equipment is selected to carry out the process pile test. The installation of equipment must meet the standards of installation plan, installation progress and acceptance report. Before construction, perfect construction scheme should be made, suitable construction technology should be selected, and necessary protective measures should be taken. According to the overall project schedule, determine the pile foundation construction scheme. Before construction, process test piles shall be conducted to determine process parameters.
1.3 preparation of pile foundation construction site
Clear the obstacles on the site to ensure that the site is flat. Before the pile driver enters the site, in order to ensure the verticality of the pile driver, the operation area must be leveled. For precast piles, the self-weight of piling machinery is large, and gravel with a thickness of about 20cm can be laid on site to better improve the bearing capacity of foundation surface and avoid uneven settlement of piling machinery. Pavement slab can also be used to reduce the pressure of foundation soil. According to the different hole-forming methods, the problem of mud pit and drainage ditch should be considered in site leveling. Arrange mud pit, mud tank and drainage ditch to ensure the improvement of construction efficiency.
1.4 Pile Foundation Construction Site
Pay-off positioning should carefully check the axis, determine the pile position control line according to the construction grid, mark each pile, and further determine the corresponding pile position. When setting sample piles on site, the pile position should be checked comprehensively, the elevation of pile foundation should be controlled according to the design requirements, the construction leveling points should be arranged outside the influence range of pile sinking, and the protection of leveling points should be paid attention to.
2. Choose a suitable pile sinking method.
2. 1 piling of precast piles
In the static pressure pile sinking construction, one-way pile sinking is the pile sinking route, which can effectively avoid the consequences of surface uplift caused by the overflow of foundation soil and avoid the problem that some piles are inclined due to the mutual extrusion of soil. In actual operation, the pile is sunk to a predetermined depth or reaches the bearing stratum, and the pile is pressed into the soil by static pressure under the condition of no vibration or noise, so as to reach the designed penetration or elevation.
2.2 Pile-forming method of cast-in-place pile
Put the prefabricated reinforcing cage into the pile hole by dry operation, pipe sinking and mud wall protection. After the pile hole is formed, concrete is poured, and the steel pipe is pulled out while vibrating and tamping to form the cast-in-place pile. In order to prevent groundwater infiltration after hole formation, concrete is poured in anhydrous environment to improve the quality of pile body.
2.3 Pile sinking methods for steel piles and concrete piles
The commonly used pile sinking methods are vibration pile sinking method, water jet pile sinking method, static pressure pile sinking method and hammering method. Among the common pile sinking methods, the vibration pile sinking method is prone to soil squeezing in the construction process. In order to avoid soil hardening, effective measures must be taken. When the pile is driven by water jet method, water injection method can be used.
3 high-rise building pile foundation construction
When pouring, it is necessary to check the preparation of building materials on the construction site and implement the construction plan. , and pay attention to the specific ratio. When checking the catheter, it must be watertight and pressure-bearing. Concrete should have good workability to ensure the quality of pile concrete. Check whether the uniformity of concrete meets the specification requirements, and continuously pour concrete to avoid hole collapse. In order to prevent the reinforcing cage from floating, the concrete pouring speed should be slowed down. If quicksand is encountered during pouring, the construction technology should be changed to improve the slump of concrete. Common quality problems in pile foundation construction generally include that the bearing capacity of a single pile is lower than the design requirements. We can take effective measures such as supplementary delivery method, supplementary pile method and composite foundation method. The first method is to repeat the problematic piles and properly fill some intact piles. The cast-in-place pile method uses the pile cap to bear the construction reaction of static pressure pile, and the operation method is relatively simple.
To sum up, the foundation of a building has a vital impact on the overall quality of the building, and the quality of pile foundation construction will directly affect the engineering quality of the whole building. At present, the main type of pile foundation in China is the pile foundation of high-rise buildings. Due to the great differences in construction geology and topography, it is necessary to make good preparations for construction and strengthen construction supervision according to the conditions of construction site and the characteristics of high-rise buildings, and choose pile types and construction methods. In the actual construction process, the most reasonable construction scheme is selected, and the construction technology and related knowledge of high-rise building pile foundation are analyzed in detail, so as to avoid undue deviation and mistakes, improve the construction quality of high-rise building pile foundation, ensure that the pile foundation meets the requirements, and make the high-rise building effect meet the required standards.
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