Keywords: construction of bored piles in the form of pile foundation in civil buildings
China Library Classification Number: TU74 Document Identification Number: A Document Number:
At present, with the rapid development of China's economy, great changes have taken place in the types, forms, equipment and design methods of piles we are in contact with. Nowadays, in areas with poor land quality, pile foundation has become a widely used foundation form for building various buildings, especially high-rise buildings. This paper mainly puts forward the matters needing attention in the construction of industrial and civil buildings from the aspects of pile foundation selection, construction technology and cast-in-place pile technology.
1 Selection of pile foundation form
When choosing the form of pile foundation, we should pay attention to many details, and a little carelessness will cause great losses. In foundation design and construction, the foundation condition of the site is an important condition for the form, size, supporting mode, shape and construction method of left and right pile foundations. Therefore, attention should be paid to the choice of pile foundation form, mainly from the following points.
(1) For hard rock-socketed piles, from the summary of some domestic equipment at present, impact drilling is better than rotary drilling.
(2) The bearing stratum is too deep, which is not conducive to manual digging piles. First, the operation is difficult; second, the cost is high and the drainage is difficult.
(3) Some weathered rocks are easy to soften when meeting water, so this problem should be considered when selecting prestressed pipe piles. In addition, this problem should also be considered when cleaning the bottom of digging piles.
(4) The geotechnical engineering geological conditions of the site have great influence on the pile foundation construction, which can't guarantee the construction safety well. At the same time, because the bearing layer is buried too deep, it is difficult to give full play to the economic advantages of pipe piles.
1. 1 precast pile
Precast pile has a strong bearing capacity and is a commonly used soil compaction pile. When piling, the surrounding soil layer is carefully treated, so the bearing capacity of pile foundation is very good. Generally speaking, it is suitable for some interlayer with loose bearing layer, and because of its strong bearing capacity, precast piles are often used in underwater pile foundation engineering. In some projects with tight construction period, precast piles can shorten the construction period. Finally, precast pile is the main choice for many pile foundation projects because of its relatively simple technology and reasonable price.
1.2 cast-in-place pile
The cast-in-place pile can adjust the length of the pile, save steel in the construction process, and the bearing capacity of a single pile is large, so it can be used for single and multiple driving. At present, cast-in-place piles are often used in high-rise residential buildings. Cast-in-place piles are divided into diamond cast-in-place piles and spiral cast-in-place piles. Two different pile foundations are suitable for different construction conditions.
High-rise buildings with excessive settlement and uneven settlement of foundation are not allowed in construction. For high-rise buildings such as chimneys, pile foundation should be used to bear uplift force and horizontal force during construction. Another important function of pile foundation is to prevent the structure from tilting. For those special lands with soft foundation or permanent buildings, we can choose pile foundation as the structural anti-seismic measures in earthquake areas. When operating large or precision equipment, attention should be paid to reducing the influence of foundation vibration on the structure as much as possible, or controlling the settlement and settlement rate of the foundation. When the soft soil is very thick or the pile tip can't reach the good stratum, the settlement of pile foundation should be considered.
2 Preparation before pile foundation construction
The specific construction technology of pile foundation is based on the quality requirements of the project, the geological conditions of the construction site and other factors, and its specific construction process mainly includes the following aspects:
(1) Construction preparation. The workload of construction preparation is very heavy, including many specific contents. Before construction, we should prepare funds according to the actual situation of specific projects and contact the construction units of each project.
(2) measuring unreeling. According to the construction drawing and the survey plane control network, the lofting pile position is measured, and then the measurement results are consolidated through the procedures of detection, retest and inspection application, and the pile position is specially protected.
(3) producing mud. In the process of construction, mud should be prepared except for the soil layer that can make mud by itself. Mud is often composed of water, soil, soda ash and so on in a certain proportion. See table 1 for mud preparation indicators. In the process of mud circulation, sediment separator should be used to control the sand content in mud, and electronic detector can be used to check the borehole to shorten the time.
Table 1
3. Pile construction in pile foundation engineering
3. 1 pile location measurement
According to the design simulation given by the design institute and the situation of the site control points, the site piles are accurately designed and laid out, and permanent marks are made to ensure the scientific and correct axis points. This paper analyzes the geographical conditions and topography of the site, sets up some lofting base points and sets up the coordinate form suitable for the terrain. By using the total station, the base points are accurate, some manual measurement errors are eliminated, and the center deviation of the pile position is controlled within10 mm.
3.2 Buried liner
The burying of liners is an important link before drilling. Although liners are not the main part of pile foundation construction, they are very important for protecting drilling holes. The gasket is made of steel plate with a diameter of about 5 mm, and the diameter varies according to the size of the hole. The inner diameter of the liner is 20 cm larger than that of the drill bit, and the depth of the liner buried in the soil is about two meters. In addition, the liner needs to be provided with overflow holes to facilitate drainage.
3.3 Drilling and punching
In the drilling process, we use GQ- 12 drilling rig, which is characterized by fast rotation speed and high penetration rate, which can greatly improve the construction progress. According to the engineering design and measurement, the depth and size of the hole are designed reasonably, and the drilling requirements are very strict. After the quality inspector has passed the self-inspection, he shall sort out relevant information and report it to the supervisor for re-inspection. When drilling, he shall sample all soil layers.
3.4 Mud wall protection
Mud wall protection is a very important job. Muddy soil and silt will have a great influence on the strength of pile foundation of the whole project. Mud wall protection is an important part of hole formation and occupies an important position in the quality of hole formation. The quality of mud wall protection directly affects the pore-forming strength. Generally speaking, silty clay has good viscosity. For this kind of soil layer, a self-made retaining wall is built during construction. However, if you encounter a soil layer with poor soil quality, you can improve the protection strength by strengthening the retaining wall. The colloid rate of retaining wall soil should be above 95%, and the sediment concentration should be within 6%.
3.5 Control of sediments
The thickness of sediment is the main bearing link, and a hole cleaning measure is mainly adopted in the construction process. A hole cleaning is to treat the open area once with a suitable drilling tool until the sediment in the open area is within 50mm, and the treatment time is about one hour. Sometimes, floating and sinking slag is also used. When dealing with floating and sinking slag, lift the drill bit and lower the reinforcing cage to control the slag within 50 mm ..
3.6 Placement of reinforcing cage
When placing reinforcing cages, the requirements for location and distance are very strict. According to the site conditions, ensure that the reinforcing cage is clean and flat. The number of main joints of reinforcing cage with the same section should be controlled within 50%, and the spacing should be greater than 50cm. Reinforcing cages can be placed in sections, and the joint length is 10dm.
3.7 Concrete pouring
The pouring time is very strict. Concrete should be poured immediately after hole cleaning, and the thickness of interstitial deposits should be checked again before pouring. If the thickness of the sediment does not meet the requirements, measures should be taken immediately to reprocess it. When pouring, the catheter should be connected with 220 threads, the water pressure should be controlled at about 65438±0 MPa, and the joint should be tight to ensure good sealing. Controlling concrete construction is a continuous process, and every fault in construction should be recorded in detail.
4 conclusion
In short, the author's years of work practice proves that in a large number of industrial and civil construction projects, pile foundation construction itself has the advantages of high bearing capacity, good stability and strong practicability, which not only saves the construction period, but also improves the construction progress and efficiency, and has been recognized and applied by people in the industry.
refer to
[1], Zeng Wen, Tao, et al. Experimental study on strengthening soft soil foundation with cement-lime mixed slurry [J]. China Waterway (second half), 20 10( 1).
Zhang. Lower bound analysis of stability of strip foundation under variable value combined loading mode [A]. Proceedings of the 14th China Symposium on Ocean (Coastal) Engineering (I) [C], 2009.
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