JP2701729B2 - Sand compaction pile method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sand compaction pile method used for ground improvement, which is required in terms of settlement and strength when performing construction on soft ground.

[0002]

2. Prior Art and Problems to be Solved by the Invention
In a clay layer having a small permeability, the speed at which pore water flows out is low, so that a so-called consolidation phenomenon is exhibited in which subsidence continues for a very long period when a load is applied. Further, such a soft clay layer has a low strength, and thus may be broken at the time of loading. Therefore, when a construction operation is performed on such soft ground, ground improvement is required in terms of settlement and strength.

[0003] As such a ground improvement, a well-compacted large-sized sand pile is formed in the soft ground as described above, and a composite ground composed of the sand pile and the cohesive soil is formed. The sand compaction pile (hereinafter referred to as SCP) method is expected to (1) increase the bearing capacity and shear strength of the sand pile itself and (2) increase the strength of the cohesive soil due to consolidation using the sand pile as a drainage layer. Is used.

[0004] This SCP method is mainly
Expecting the improvement effect of (1), construction with "high replacement rate", where sand replacement rate is about 70%, was common. However, if the superstructure is relatively small or the construction period can be prolonged, the effect of the above (2) is expected to be achieved by "low replacement ratio" in which sand displacement is suppressed to about 30%. It is also economically advantageous.

[0005] Therefore, recently, the SCP having a low substitution rate has been developed.
The construction method is heavily used. However, if the consolidation time can be shortened and the effect of increasing the strength of the cohesive soil between sand piles can be quickly achieved even at this low displacement rate, it can be said that the construction is more effective.

However, the conventional S
In the CP method, a large amount of clay exists between each of the sand piles formed to perform the ground improvement, which makes it difficult to achieve the above-described task of shortening the consolidation time.

[0007] In detail, in the SCP method which has been generally performed conventionally, as shown in FIG.
Is supplied through a casing pipe 23 having a substantially circular cross-section provided with a vibrator 22 such as a vibratory hammer, and as shown in FIG. Also has a circular cross section. Therefore, a large amount of clay exists between each of the sand piles 20 in the sand pile group 24.

The large amount of clay between the sand piles 20 makes it difficult to achieve the above-mentioned problem of shortening the consolidation time, that is, the effect of increasing the strength of the cohesive soil between the sand piles quickly. This makes it difficult to shorten the consolidation time required to achieve it.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to quickly achieve the effect of increasing the strength of the cohesive soil existing between sand piles during soil improvement for forming sand pile groups. Therefore, while the consolidation time can be shortened reliably, the SCP method is often used to improve loose sand ground as a countermeasure against liquefaction. It is an object of the present invention to provide a sand compaction pile method capable of exerting an effect.

[0010]

According to the present invention, a plurality of radially extending projections are provided at the tip of a pipe body having a substantially circular cross section in a casing pipe for supplying sand for forming a sand pile into the ground to be improved. Is provided so that a plurality of projecting portions are formed on the circular base in the cross-sectional shape of each sand pile formed by the casing pipe.

According to the method of the present invention,
The multiple projecting portions of each sand pile described above increase the water collection area in the case of clay ground, shorten the clay drainage distance between each sand pile, and promote high compaction in the ground where each sand pile is formed. Be effective. On the other hand, in the case of a loose sandy ground, the protruding portion of each sand pile makes it possible to exert the compaction effect also on the sand between the piles.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The sand compaction pile method according to the present invention will be described below with reference to the illustrated embodiment (when used on clay ground).

First, the casing pipe used in the method of the present invention will be described. The casing pipe 1 (FIG. 1A)
And (b)) is a pipe body 1a having a substantially circular cross section.
A plurality of radially extending portions (in this embodiment, 90 °
(Four places each) 1b. In the sectional shape of each sand pile 2 formed by the casing pipe 1, a plurality of projecting portions 2b are formed on a circular base 2a as shown in FIG. 1 (c).

In the embodiment of FIG. 1, (c) of FIG.
As shown in FIG. 1, a square pile type sand pile group 3 in which each sand pile 2 is arranged in a substantially square shape. In contrast, FIG.
The casing pipe 1 of the embodiment shown in (a) and (b)
As shown in FIG. 2 (b), protrusions 1b are provided at three positions every 270 °, and as shown in FIG. 2 (c), the sand piles 2 are arranged in a staggered manner. Sand pile group 3.

In order to perform the sand compaction pile method using the casing pipe 1 having such a configuration, a vibrator (not shown) such as a vibro hammer is provided in the ground to be improved. This is performed by supplying sand for forming a sand pile through the casing pipe 1.

At this time, a plurality of projections 1b extending radially are provided at the tip of the pipe body 1a having a substantially circular cross section in the casing pipe 1 (see FIGS. 1A and 1B). A plurality of projecting portions 2b are formed on the circular base 2a also in the sectional shape of each formed sand pile 2 (see FIG. 1 (c)).

The plurality of projecting portions 2b of each of the sand piles 2
Thereby, the water collecting area is enlarged, and a large amount of clay does not exist between the sand piles 2 in the formed sand pile group 3. From this, the drainage distance of the clay between the sand piles 2 can be further reduced at the protruding portion 2b, and a high consolidation promoting effect can be obtained in the ground on which each sand pile 2 is formed.

[0018]

According to the sand compaction pile method of the present invention, by providing a plurality of projections extending radially at the tip of the casing pipe, a projecting portion is also formed on each sand pile formed by the casing pipe. , The area of the catchment can be expanded.

That is, the drainage distance of the clay between the sand piles in the sand pile group is further shortened, and a further consolidation promoting effect can be obtained.

[Brief description of the drawings]

FIG. 1 (a) is a schematic sectional view showing a casing pipe used in a sand compaction pile method of the present invention.
(b) is a sectional view taken along line AA of (a), and (c) is a schematic view showing a group of sand piles formed by the casing pipe of (a).

2A is a schematic sectional view showing another embodiment of a casing pipe used in the sand compaction pile method of the present invention, FIG. 2B is a sectional view taken along line BB of FIG. 2A, and FIG. It is the schematic which shows the sand pile group formed of the casing pipe of (a).

FIG. 3 is a schematic view showing a sand compaction pile method.

FIG. 4 is a schematic view showing a group of sand piles formed by casing pipes in a conventional sand compaction pile method.

[Explanation of symbols]

1 ... casing pipe, 1a ... pipe body, 1b ... protrusion, 2
... sand piles, 2a ... base, 2b ... projecting parts, 3 ... sand piles.

Claims (1)

(57) [Claims] 1. A sand compaction pile method for feeding sand for forming a sand pile into a ground to be improved through a casing pipe provided with a vibrator such as a vibro hammer. A plurality of projections extending radially are provided at the tip of the pipe main body, and a plurality of protrusions are formed at a circular base in the cross-sectional shape of each sand pile formed by the casing pipe. The multiple projecting portions of the piles increase the catchment area and prevent large amounts of clay or loose sand as the ground between each sand pile in the formed sand pile group. The drainage distance of the clay between the piles can be further reduced at the protruding portion so that a high consolidation promoting effect can be obtained in the ground where each sand pile is formed, and Sand compaction pile method characterized in that the compaction effect and efficiently.