Pile forming method for high-bearing two-stage bottom expanding prefabricated pile body

Abstract

The present invention relates to construction of building pile foundation engineering, and is especially piling process of two-stage under-reamed prefabricated pile stem with high bearing capacity. The piling process includes the following steps: 1. immersing immersed tube with metal pile head into hardpan to design elevation; 2. taking out the metal pile head; 3. forming the lower base space with blasting and under reaming apparatus and pouring the lower base with concrete; 4. setting the prefabricated hollow pile stem with steel dowels into the immersed tube; 5. drawing upwards the immersed tube to designed distance, forming the upper base space, penetrating the steel dowels through the upper base space and connecting to the lower prefabricated pile stem, setting the upper prefabricated pile stem into the immersed tube, and pouring the upper base; and 6. withdrawing the immersed tube and injecting cement mortar to the gap.

Description

technical field [0001] The invention relates to a construction method of a building pile foundation project, in particular to a pile forming method of a prefabricated pile body with two-stage bottom expansion. Background technique [0002] According to the national standard, the whole body is cast-in-place (that is, the pile body is cast-in-place concrete, and the base is also cast-in-place concrete). The maximum diameter ratio of the base of the expanded bottom pile is limited to 3-3.5, while the immersed tube prefabricated steel concrete expanded bottom pile, this kind of pile It is prefabricated concrete for the pile body and cast-in-place concrete for the base. Obviously, the ratio of 3-3.5 is broken, and generally can reach 3.5-5. Although the bearing capacity is greater, it still cannot meet the needs of the project, especially when the diameter of the expanded bottom is greater than 1.5 meters. , the end bearing capacity should be discounted by 0.9. For this reason, ...

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Problems solved by technology

These two points are quite unfavorable to multi-bearing plate (multi-level bottom expansion) piles. In other words, it brings two problems. 1) The national building code stipulates that the end bearing of the base of the pile expansion bottom using the positive and negative circulation method The force has to be multiplied by a factor of 0.45, because there is mud and the sediment at the bottom of the pile cannot be cleaned up. (The standard in Zhejiang Province is 0.24 discount). However, the construction conditions cannot be protected. In addition, the positive and negative circulation method works underwater, so the bottom expansion construction cannot be seen, and it is difficult to measure and record. It also often happens that a piece of upper soil falls off when the bottom is expanded underwater. Occurrence, also because the multi-stage piles of the prior art all use cast-in-place concrete for the whole body, and the strength of cast-in-place concrete is not high, and the quality is difficult to guarantee, and the quality is difficult to control when pouring concrete in water, plus multiple bases The bearing capacity of the piles is relatively large, the diameter of the pile body must be made larger due to the above factors, and this kind of multiple bases is most afraid of a large diameter of the pile body. Research and tests have shown that as the diameter of the pile body increases, its bearing capacity will be greatly attenuated.

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