JP4425073B2 - Cast-in-place concrete construction method - Google Patents

Description

The present invention relates to facilities coating method of cast-in-place concrete piles.

For cast-in-place concrete piles, depending on the excavation method, (1) rotating bucket stable liquid normal circulation method [earth drill method], (2) rotating bit drilling mud reverse circulation method [reverse method], (3) hammer grab picking method [ There are four types of typical construction methods: “all casing construction method” and (4) mechanical excavation method [deep foundation] such as manpower or dedicated clamshell.
These cast-in-place concrete piles are excavated with a predetermined cross-section with a predetermined accuracy, and then subjected to slime treatment to build a reinforcing steel cage, and concrete is sequentially launched upward from the bottom of the excavation hole by the tremmy method. Has been built.

With cast-in-place concrete piles, large diameter (2-4 m in diameter) and large depth (50-70 m in depth) are planned from the ground conditions as the size and height of the building grows. Expanded piles that make the pile diameter larger than the pile shaft deeper due to bending and shearing stress (usually a depth range of 3 to 5 times the pile diameter), and install a thick-walled steel pipe outside this reinforcing bar Pile methods and shapes are rationally selected according to the degree of load to be borne, such as steel-pipe cast-in-place piles and widened piles that widen the pile tip and increase the pile bearing strength.
In the conventional cast-in-place concrete piles, the concrete strength is conventionally determined by the bending and shearing stress that is maximum at the pile head, and the same concrete mix (mixing) and strength are applied to the pile bottom where only the axial compression force acts. (For example, Patent Document 1).
JP 2004-124368 A

Therefore, in conventional cast-in-place concrete piles, the concrete strength is determined based on the pile head where the bending and shear stress of the largest value acts, and therefore, at the pile shaft and the pile bottom below the pile head. It has an unnecessary strength far exceeding the necessary and sufficient strength, and has a disadvantage that the cost increases accordingly.
The present invention has been devised in view of the above circumstances, and an object of the present invention is to have a necessary and sufficient strength over the entire length in the depth direction from the pile head to the pile bottom and to reduce the cost. It is to provide a facilities application method of cast-in-place concrete as possible.

The order to achieve the object the present invention inserts a tremie pipe to drilling drilling, upon which concrete is cast into the wellbore from tremie pipe, while buried the tip of the tremie tube in existing punch set concrete tremie pipe In the construction method of cast-in-place concrete piles to be pulled up, the amount of cement in the concrete to be placed is increased as it goes to the bottom of the pile body, the middle part of the pile body, and the head of the pile body , and at the time of concrete placement The slump value of the cast concrete in the pile body is larger in the middle part of the pile body than in the bottom part of the pile body, and larger in the head part of the pile body than in the middle part of the pile body. Change to increase,
Furthermore, when placing concrete in the pile head, the vibrator is operated to compact the placed concrete so as to improve the solidity .

  According to the present invention, the concrete mix is changed so that the required strength is exhibited according to each part of the cast-in-place concrete pile. Therefore, the pile body is rational in terms of material costs while ensuring the necessary strength. Construction is possible.

The present invention achieves the above object by increasing the amount of cement in the concrete as it goes to the pile bottom, the middle pile, and the pile head.
Hereinafter will be described the construction how the place concrete piles of the present invention according to FIG surface.

FIG. 1 is an explanatory view of a method for constructing a cast-in-place concrete pile according to Example 1, and shows a flow state at the time of placing concrete by the tremy method.
In FIG. 1, reference numeral 10 denotes the ground, reference numeral 12 denotes a drilling hole 12 excavated in the ground, reference numeral 14 denotes the ground surface, and reference numeral 16 denotes a tremy tube.
The cast-in-place concrete pile 20 is formed by placing concrete in the excavation hole 12.
As for the cast-in-place concrete pile 20 of a present Example, the cement amount in concrete is increasing as it goes to the pile bottom 20A, the pile intermediate part 20B, and the pile head 20C.
When the cast-in-place concrete pile 20 is constructed, the tremy pipe 16 is inserted into the excavation hole 12, and concrete is cast from the tremy pipe 16 into the excavation hole 12. At that time, the tip of the tremy pipe 16 is placed in the already-cast concrete. While burying, the tremy tube 16 is pulled up step by step.
Then, the amount of cement in the concrete to be placed is increased as it goes to the pile body bottom portion 20A, the pile body intermediate portion 20B, and the pile body head portion 20C.
The inner diameter and length of the tremmy pipe 16 used for placing concrete are as follows. That is, the inner diameter of the tremy tube 16 is usually 8 mm (203 mm), 10 mm (254 mm), or 12 mm (305 mm) depending on the pile diameter. The length of the tremmy pipe 16 is 1m, 2m, 3m, 5m, etc., and the height of the pile bottom, middle, and pile heads is about 20cm above the pile bottom to the height of the construction ground. Those of 3 m, 5 m, etc. are used in appropriate combination.

In the construction of the cast-in-place concrete pile 20 using the above-described tremy pipe 16, first, the concrete filled in the tremy pipe 16 is driven to the bottom of the excavation hole 12 by pushing up a stabilizing liquid or mud water.
Next, the concrete to be placed is placed so that the already placed concrete is pushed horizontally from the peripheral portion of the tip portion of the tremmy pipe 16 so as to cover the concrete. The shape of the peripheral part is slightly lower and gradually rises as it reaches the inner wall of the excavation hole 12. More specifically, the shape of the borehole 12 gradually rises from the center to the outer periphery, and the height difference between the center and the outer periphery is about 20 to 50 cm due to the workability of the concrete.
The concrete is continuously cast to the designed pile ceiling while the tip of the tremy pipe 16 is always buried in the cast concrete by about 2 to 5 m.
The cast concrete begins to harden sequentially under the weight of concrete placed above it (5 times the height of the pile diameter method) and hardens until it becomes self-supporting after 2 to 5 hours. To do.

In concrete pouring by the trememy method, the tremely pipe 16 is pulled up while controlling the depth of burying of the tremy pipe 16 in the cast concrete according to the concrete pouring height (extracting the tip of the tremy pipe 16). It has been cast in layers.
From such a concrete placement situation, it is possible to construct a more rational pile body by blending (mixing) the pile body concrete according to the required strength.
As the composition (mixing) of pile-casting concrete goes to the pile bottom 20A, pile intermediate 20B, and pile head 20C, the amount of cement is increased, and the necessary strength is obtained by continuously casting. Build a pile structure. For that purpose, the following three items are important.
(1) The concrete launch surface is placed so as to be close to the level (inside / outside difference of 30 cm).
For this purpose, the diameter of the tremy tube 16 is appropriately determined according to the pile diameter. For example, when the pile diameter is less than 2000 mm, the tremey pipe 16 having a pipe diameter of 10 mm is used, and when the pile diameter is 2000 mm or more, the tremey pipe 16 having a pipe diameter of 12 mm is used, To secure.
In addition, workability of cast concrete will be properly managed. For example, the slump value is set to 17 to 18 cm in the pile body bottom 20A, the slump value is set to 18 to 19 cm in the pile intermediate part 20B, the slump value is set to 19 to 20 cm in the pile body head 20C, and the fluidity is increased toward the top.
(2) Mixing (mixing) of the cast concrete is changed from about 2 m below the planned change site (mixing). That is, the mixing of the concrete is changed from the lower part of the boundary part between the pile body bottom part 20A and the pile intermediate part 20B and the boundary part between the pile intermediate part 20B and the pile head part 20C from the lower part.
This is to ensure that the mixing (mixing) change planned portion of the cast concrete is set as planned (mixing) as planned, and the tube insertion length of the tremy pipe 16 into the cast concrete is also within 2 m. In addition, the configuration of the tremy tube 16 is planned in advance.
(3) A vibrator is used in the concrete placement of the pile head 20C.
This is because, in the pile head 20C, the concrete strength tends to decrease due to the self-weight compaction action of the cast concrete and the fluidity of the concrete being reduced. Therefore, the cast concrete of this part is compacted. In order to increase the solidity, the high frequency vibrator installed in advance is operated after the concrete placement is completed.

A cast-in-place concrete pile 20 having a pile diameter of 2 m and a length of 17.5 m was constructed under the conditions shown in Table 1 by the tremy method while carrying out the above (1) to (3).
Table 2 shows the high-performance AE water reducing agent, AE water reducing agent, and usable AE water reducing agent.

  Table 3 shows the strength of the obtained concrete piles.

  As is apparent from Tables 1 and 3, according to this example, the pile has a necessary and sufficient strength over the entire length in the depth direction from the pile body bottom 20A to the pile body head 20C. It is possible to reduce the amount of cement to be used while securing a desired strength in the concrete pile 20, and it is possible to reduce material costs. That is, it is possible to reduce the cost of foundation work using the cast-in-place concrete pile 20, which is extremely advantageous in reducing the cost of the structure using the cast-in-place concrete pile 20.

It is explanatory drawing of the construction method of a cast-in-place concrete pile.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Ground, 12 ... Excavation hole, 14 ... Ground surface, 16 ... Tremy pipe, 20 ... Cast-in-place concrete pile, 20A ... Pile body bottom part, 20B ... Pile body middle part, 20C ... Pile Body head.

Claims (2)

In the cast-in-place concrete pile construction method, when inserting the tremely pipe into the excavation hole and placing concrete from the tremey pipe into the excavation hole, the tremely pipe is pulled up while the tip of the tremee pipe is buried in the already placed concrete. ,
Increase the amount of cement in the concrete to be placed as you go to the bottom of the pile, the middle of the pile, and the head of the pile ,
In addition, the slump value of the cast concrete at the time of placing the concrete is set so that the pile body middle part is larger than the pile body bottom part, and the pile body head part is larger than the pile body middle part and the upper part is driven. Change to improve the fluidity of concrete,
In addition, when placing concrete in the pile head, the vibrator was operated to compact the placed concrete, increasing the solidity.
The construction method of the cast-in-place concrete pile characterized by this. The length of the tremely pipe inserted into the cast concrete at the time of concrete placement is maintained at 2 m inside and outside, the boundary part between the bottom of the pile body and the intermediate part of the pile body, and the intermediate part of the pile body and the pile body construction method of in-place concrete piles of claim 1, wherein the lower portion each as 2m bordering parts of the head, to change the formulation of the concrete.

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