JPH04265312A - Method of multistage bottom-expanding place pile driving construction - Google Patents

Abstract

PURPOSE:To compact a pile by forming a plurality of bottom expanding sections corresponding to a stratum having bearing power at a plurality of positions in the longitudinal direction of the pile. CONSTITUTION:A stratum at a pile execution position is investigated by boring, etc., and the stratum 3 of a positive support layer, stratums 4a, 4b, 4c having no bearing power and stratums 5a, 5b having certain bearing power are confirmed. Pile pits 8 with bottom expanding sections are excavated to the stratums 5a, 5b by using a bottom expanding bit 6, etc. Slime is treated and a reinforced cylinder 7 is hung down, and concrete is placed and multistage place driving piles with bottom expanding sections are formed at a plurality of positions in the longitudinal direction. Accordingly, since bearing power required can be ensured in the total of the bearing power of each bottom expanding section, pile length can be shortened while a pile diameter can be reduced even when the pile reaches the positive support layer, the term of work can be shortened, and the cost of construction can be economized.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved cast-in-place pile construction method with an expanded bottom.

0002

[Prior Art] The method of increasing the diameter of the tip of a pile in order to increase the bearing capacity of each cast-in-place pile is already known as the expanded-bottom cast-in-place pile method, and there are many examples of its construction. .

However, in the above-mentioned expanded-bottom cast-in-place pile construction method, the circumferential friction force of the shaft is generally not included in the bearing capacity, so ready-made piles such as PC piles are installed in the middle of the excavated ground. In some cases, even if there is a stratum that is considered to have sufficient bearing capacity, the expanded bottom part of the tip of the pile is located below the stratum with a solid support layer (support that is required only by the tip bearing capacity). It was established in a stratum with a large supporting capacity that could provide sufficient support.

[0004] For this reason, in the conventional cast-in-place pile construction method with an expanded bottom, the pile length must be extremely long, and as a result of the concept of supporting the entire upper load at the tip of the pile, naturally the expanded bottom portion The diameter of the piles in the shaft section also increased, posing problems in terms of both construction time and construction costs.

[0005]

[Problems to be Solved by the Invention] In view of the above-mentioned current situation, the present invention makes it possible to utilize the bearing capacity of a plurality of strata.
This project proposes a multi-stage cast-in-place pile construction method that shortens the construction period and reduces construction costs.

[0006]

[Means for Solving the Problems] In order to solve the above problems, in the present invention, a plurality of expanded bottom portions are formed at a plurality of locations in the longitudinal direction of a cast-in-place pile, corresponding to strata that can be expected to have a supporting capacity. The necessary supporting force is ensured by the plurality of enlarged bottom parts.

[0007]

[Function] According to the above configuration, the plurality of expanded bottom portions formed at multiple locations in the longitudinal direction of the cast-in-place pile are supported by the plurality of strata corresponding to the expanded bottom portions, and the total supporting capacity of these portions is This ensures sufficient bearing capacity, making it possible to shorten the pile length.Also, even when the pile length reaches a solid support layer, the diameter of the pile at the shaft can be made smaller. It is.

[0008]

Embodiment FIG. 1 shows a comparison between a multi-stage expanded-bottom cast-in-place pile 1 according to the present invention and a conventional expanded-bottom cast-in-place pile 2, and FIG. 2 shows an example of the construction procedure. In the figure, 3 is a stratum with a large bearing capacity that can serve as a solid support layer, 4a, 4b
, 4c are strata that cannot be expected to have a bearing capacity, and 5a and 5b are strata that can be expected to have a certain degree of bearing capacity, although they are smaller than the solid bearing layer (stratum 3). In FIG. 2, 6 indicates a bottom expansion bit, and 7 indicates a reinforcing bar cage.

As shown in FIG. 1, the multi-stage expanded bottom cast-in-place pile 1 has a plurality of expanded bottom portions 1a and 1b formed at multiple locations in the longitudinal direction corresponding to the strata 5a and 5b that can be expected to have a bearing capacity, The plurality of enlarged bottom portions 1a and 1b are configured to ensure necessary supporting force.

That is, prior to the construction of the multi-stage expanded bottom cast-in-place pile 1, a soil profile map and soil property map of the ground to be constructed are created by sampling by boring, penetration tests, etc., and the N value of each layer, soil quality, and multi-stage Based on the load borne by the expanded-bottomed cast-in-place pile 1, etc., the strata 3 that can serve as a reliable support layer and the strata 5a and 5b that can be expected to have bearing capacity are confirmed.

[0011] The depth of the stratum 3 that can serve as a reliable support layer is deep, and the stratum 5a, which can be expected to have a supporting force above it,
5b is confirmed, pile holes having large diameter portions are excavated in the ground at desired depths. For example, as shown in FIG. 2, the enlarged bottom bit 6 may be enlarged to correspond to the strata 5a, 5b, or the enlarged bottom bit 6 may be reduced to correspond to the strata 4a, 4b, 4c. Change the excavation radius and form the pile hole 8.

[0012] Next, slime treatment and suspension of the reinforcing bar cage 7 are carried out in this order or in the reverse order, and concrete is poured to form the first stage expanded bottom portion 1a corresponding to the above-mentioned stratum 5a. , a multi-stage expanded-bottom cast-in-place pile 1 with a second-stage expanded-bottom portion 1b formed in correspondence with the geological layer 5b;
The plurality of enlarged bottom portions 1a and 1b ensure the necessary supporting force.

For example, as shown on the right side of FIG. 1, the N value of the solid support layer (stratum 3) is 50, and the N value of the stratum 5a is 2.
5. If the N value of the stratum 5b is 35, the first stage expanded bottom part 1
a is fixed in the stratum 5a with an N value of 25, and the second stage expanded bottom part 1
b is fixed in the stratum 5b with an N value of 35, so as a total of these, the conventional cast-in-place pile 2 with a solid support layer (stratum 3) as a single support layer as shown on the right side of Fig. 1.
A supporting force comparable to or greater than that can be obtained.

[0014] Although not shown in the drawings, even if the excavation depth is increased and the bottom expanded portion is anchored to a firm support layer (gear layer 3), as in the case of the conventional expanded-bottom cast-in-place pile 2,
The upper load acting on the multistage expanded bottom cast-in-place pile 1 is
Since it is also supported by a and 5b, the load borne by the pile tip is reduced, and the pile diameter of the shaft portion 1c on the pile tip side can be reduced.

[0015] Therefore, in any of the above cases, it is possible to shorten the construction period and reduce construction costs.

In the above embodiment, the shaft portion 1c of the multi-stage expanded bottom cast-in-place pile 1 is also excavated using the bottom expansion bit 6, but the shaft portion 1c is excavated and formed using the conventional earth drilling method, It may also be carried out by the Benoto construction method or the like.

FIG. 3 shows another embodiment of the invention. This embodiment is characterized in that the above-mentioned multi-stage expanded-bottomed cast-in-place pile 1 does not have an expanded bottom portion at the tip of the pile, but is made long enough to reach a firm support layer (stratum 3). .

According to this embodiment, the plurality of enlarged bottom portions 1a, 1b formed in the longitudinally intermediate portion of the pile body are connected to the strata 5a, 5.
b, and the tip of the pile is supported by the solid support layer 3, ensuring the necessary total supporting force. The other configurations are the same as in the previous embodiment.

FIG. 4 shows another embodiment of the invention. This example shows two cases in which the strata 5a, 5b, and 5c (the lowest stratum 5c) is a reliable support layer, and the other is a stratum in which a support force can be expected although it is not as strong as the support layer. ), a plurality of enlarged bottom portions 1a, 1b, 1 are provided.
n, and these enlarged bottom portions 1a, 1b, 1n
The shaft portion 1c divided into multiple stages by the lower stage is
The feature is that the pile diameter is small.

According to this embodiment, the diameter of the pile is large near the pile head where a bending moment acts during an earthquake, and the diameter of the pile decreases toward the bottom. Coupled with the fact that the pile length and diameter of the pile 1 can be reduced, there is an advantage that the pile 1 can be realized economically. The other configurations are the same as in the previous embodiment.

[0021]

[Effects of the Invention] According to the present invention, a plurality of expanded bottom portions formed at multiple locations in the longitudinal direction of a cast-in-place pile are supported by a plurality of strata corresponding to the expanded bottom portions, and the total supporting capacity of these portions is Since the necessary bearing capacity is secured, it is possible to shorten the pile length, and even if the pile length reaches a solid support layer, the diameter of the pile shaft can be made smaller. It is possible to shorten the construction period and reduce construction costs.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of a multi-stage cast-in-place pile construction method showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an example of the construction procedure of a multi-stage expanded bottom cast-in-place pile.

FIG. 3 is a schematic cross-sectional view of a multi-stage cast-in-place pile with an expanded bottom showing another embodiment of the present invention.

FIG. 4 is a schematic cross-sectional view of a multistage cast-in-place pile with an expanded bottom showing another embodiment of the present invention.

[Explanation of symbols]

1 Multi-stage cast-in-place pile with expanded bottom 1
a, 1b Expanded bottom part 3, 5a, 5b Strata

Claims (1)

[Claims] [Claim 1] At multiple locations in the longitudinal direction of the cast-in-place pile,
A multi-stage cast-in-place pile construction method with an expanded bottom, which is characterized by forming a plurality of expanded bottom portions corresponding to strata that can be expected to have bearing capacity, and ensuring the necessary bearing capacity with the plurality of expanded bottom portions.