JP2000110179A - Method for constructing underwater foundation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of trouble such as a hindrance to common use even when additional load, etc. work after construction. SOLUTION: A foundation body 10 manufactured on a manufacturing yard is transported up to the point of installation, and the transported foundation body 10 is settled into an underwater ground A by working ballast load or working a suction by decompression. Water absorption devices such as a drainage pump are installed on the upper end sides of drainage ditches 16 after collecting drain sections 14 mounted at the lower ends of skirt sections 12 reach a bearing ground layer C at that time, and pore water in the bearing ground layer C is pumped up and drained positively.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for constructing an underwater foundation, and more particularly to a method for constructing an underwater foundation in which a skirt portion penetrates into the underwater ground.

[0002]

2. Description of the Related Art When constructing a substructure underwater, if the substructure is a pile foundation, it is generally constructed by using impact or vibration as a pushing force. However, when the foundation structure is large and the construction site is deep, there is a limit to the pushing in by hitting or vibration, and it is very difficult to adopt the pile foundation under such conditions. Become.

[0003] Therefore, when constructing a large-scale substructure at a large depth in water, a substructure integrally formed with a skirt portion at a lower end is subjected to an additional ballast load on its own weight,
Alternatively, a method of forcibly penetrating into the underwater ground by applying suction or the like is employed.

However, such an underwater foundation construction method has the following technical problems.

[0005]

That is, when the skirt portion is penetrated into the underwater ground and the substructure is installed,
Due to additional load of the structure after installation, if there is a viscous soil layer below the tip where the skirt part penetrates, the ground will cause consolidation settlement, settlement will continue even after the completion of the structure, and the amount of settlement is allowable There was a possibility that troubles such as exceeding the value or inclining would occur, which would hinder the operation of the structure.

The present invention has been made in view of such a conventional problem, and has as its object the purpose of the present invention being such that even if an additional load or the like is applied after construction, operation of the apparatus is hindered. An object of the present invention is to provide an underwater foundation construction method that does not cause any trouble.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides an underwater body in which a skirt portion is integrally formed at a lower end of a base body installed in water, and the skirt portion penetrates into a submarine ground. In the foundation construction method, a water collecting drain portion is provided at the lower end of the skirt portion, and water collected in the water collecting drain portion is discharged outside through a drain passage provided in the skirt portion. I did it. According to the construction method of the underwater foundation configured as described above, the drainage drain portion is extended at the lower end of the skirt portion, and the water collected in the drainage drain portion is passed through a drain passage provided in the skirt portion. ,
Since the water is discharged to the outside, the consolidation settlement of the underwater ground in the lower part of the skirt portion is promoted. Therefore, even if an additional load or the like is applied after the foundation is constructed, it is possible to prevent the settlement from occurring so as to hinder service. The drainage drain section,
The drain pipe may be constituted by a drain pipe communicating with the drain passage and having a through hole formed in an outer peripheral surface thereof, a filter material provided in the drain pipe, and a water permeable material filled in the drain pipe. According to this configuration, it is possible to perform drainage for promoting consolidation settlement while preventing inflow of earth and sand by the filter material.

[0008]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG.
FIG. 4 to FIG. 4 show an embodiment of the construction method of the underwater foundation according to the present invention.

The underwater foundation shown in FIG. 1 includes a foundation body 10 installed underwater and a skirt portion 12. The base body 10 includes a plate-shaped upper plate 10a and cylindrical inner and outer walls 10b, 10 provided integrally with a lower end of the upper plate 10a.
c, and a plate-shaped lower plate 10d provided so as to close the lower ends of the inner and outer walls 10b and 10c.

The basic body 10 thus constructed has a horizontal or circular cross section formed therein.
Upper and lower plates 10a, 10d and inner and outer walls 10b, 10c
And a compartment 10e is provided.
The inside is filled with seawater which becomes a ballast load when the underwater foundation is laid.

In the case of the present embodiment, the lower plate 10d is formed to have a curved surface with a predetermined curvature.

As will be described later, the skirt portion 12 penetrates into the underwater ground. In this embodiment, the skirt portion 12 is connected to the lower ends of the inner and outer walls 10b and 10c of the foundation body 10. The inner and outer walls 10b and 10c are formed of a plurality of solid cylinders having the same thickness and located on the same straight line and extending integrally downward.

In the case of this embodiment, the skirt 1
A plurality 2 are arranged at predetermined intervals from each other along the circumferential direction of the inner and outer walls 10b and 10c.

The basic structure of the underwater foundation as described above is the same as that of a conventional foundation of this type, but the underwater foundation of this embodiment has remarkable features in the following points.

That is, on the underwater foundation of this embodiment, a water collecting drain portion 14 is provided at the lower end of the skirt portion 12, and the water collected by the water collecting drain portion 14 is provided on the skirt portion 12. The water is discharged to the outside through the drain passage 16.

FIGS. 3 and 4 show details of the water collecting drain section 14. FIG.
Is shown in The drainage part 14 shown in the figure includes a drain pipe 14a, a filter material 14b, and a water permeable material 14b.
c.

The drain pipe 14a is a cylindrical body having a closed lower end, or a tubular body having a closed cross section such as a square or an ellipse, and a plurality of slit holes 14d are formed in the side surface thereof. Each drain pipe 14a is connected to each skirt 12
The upper end is supported by being fixedly attached to a mounting steel tube 18 fitted and fixed to the lower end of the cylinder.

A drain passage 16 extending in the vertical direction is provided in each skirt portion 12, and the drain passage 16 and the inside of the drain pipe 14a communicate with each other.

A drain passage 16 extends vertically through the inside of the skirt portion 12, extends to an intermediate position between the inner and outer walls 10b and 10c, and has a valve connected to a junction pipe 17 whose upper end is vertically provided at the center of the upper plate 10a. Are connected to each other with an interposition.

The drain pipes 14a attached to the lower ends of the skirts 12 are mutually connected by connecting members 18 arranged in the circumferential and radial directions. Filter material 14b
Is provided on the inner surface side of each drain pipe 14a and is formed of a tubular body such as a wire mesh, a synthetic resin mesh, or a nonwoven fabric having a function of transmitting only moisture.

The water permeable material 14c is made up of filled sand, gravel, crushed stone, a small block of synthetic resin, and the like.
4b is filled in the installed drain pipe 14a.

A method of constructing the underwater foundation constructed as described above will be described. The base body 10 includes a skirt 12
And it is manufactured in a manufacturing yard in a state where the water collecting drain portion 14 is integrally attached.

The manufactured base body 10 is transported to an installation point by a towing ship or the like. The base body 10 transported to the installation point is subjected to a ballast load by injecting seawater or the like into the compartment 10e, placing a counterweight, or the like, and by applying a suction by depressurization to the underwater ground. Set aside in A.

In this case, after the drainage portion 14 reaches the support ground layer C, the confluence pipe 17 on the upper end side of the drain passage 16 is formed.
In addition, a water absorption device such as a drain pump is connected and installed to positively pump and drain pore water in the supporting ground layer C.

In the embodiment shown in FIG. 1, the support ground layer C has a sandy soil layer C1 and a cohesive soil layer C2 formed alternately.

After performing such a drainage treatment for a predetermined period, an additional structure 22 such as a pier is constructed on the upper side of the foundation body 10.

According to the construction method of the underwater foundation performed as described above, the drainage drain section 14 is provided at the lower end of the skirt section 12, and the water collected in the drainage drain section 14 is supplied to the skirt section. When the water is discharged to the outside through the drain passage 16 provided in the base 12, the pore water pressure is reduced by the drainage, the preload effect of the underground ground A on the supporting ground layer C is exerted, and the skirt portion 12 is supported. Consolidation settlement in the ground layer C is promoted.

Therefore, even if an additional load or the like acts on the foundation after the foundation has been constructed, it is possible to prevent the occurrence of settlement that would hinder service. Also, if the consolidation settlement of the ground layer C supporting the skirt portion 12 is actively promoted, a reliable supporting ground can be secured early and a stable foundation can be secured early.

Such an operation and effect is as follows.
Even when the sandy soil layer C1 and the cohesive soil layer C2 are in an alternate layer state, the effect is effectively exerted, and the cohesive soil layer C2 can be compacted at an early stage.

In the case of the present embodiment, the water collecting drain portion 14 communicates with the drain passage 16 provided in the skirt portion 12 and has a drain pipe 14a having a through hole formed on the outer peripheral surface.
And a filter material 14b provided in the drain pipe 14a and a water permeable material 14 filled in the drain pipe 14a.
Since the filter material 14b is used, it is possible to prevent the inflow of earth and sand by the filter material 14b, and to perform drainage for promoting consolidation settlement.

[0031]

As described above in detail in the embodiments,
ADVANTAGE OF THE INVENTION According to the construction method of the underwater foundation concerning this invention, even if an additional load etc. act after construction, the trouble which hinders service does not generate | occur | produce.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a completed construction state showing one embodiment of a method of constructing an underwater foundation according to the present invention.

FIG. 2 is a sectional view taken along line AA of FIG.

FIG. 3 is an enlarged sectional view of a portion B in FIG. 1;

FIG. 4 is an enlarged view of a portion C in FIG. 2;

[Brief description of reference numerals]

 DESCRIPTION OF SYMBOLS 10 Foundation main body 12 Skirt part 14 Drainage part 16 Drainage passage

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Naoki Masui 2-3 Kandajimachi, Chiyoda-ku, Tokyo Obayashi Corporation Tokyo head office F-term (reference) 2D043 CA04 CA12 DA04 DD09 DD18 EB05 2D046 DA63

Claims (2)

[Claims] 1. A method of constructing an underwater foundation in which a skirt portion is integrally formed at a lower end of a base body installed in water and the skirt portion penetrates into a bottom of a water bottom, wherein a drainage drain portion is provided at a lower end of the skirt portion. A method for constructing an underwater foundation, wherein water collected in the water collecting drain portion is discharged to the outside through a drain passage provided in the skirt portion. 2. A drain pipe communicating with the drain passage and having a through hole formed in an outer peripheral surface thereof, a filter material provided in the drain pipe, and the drain pipe being filled in the drain pipe. The construction method of an underwater foundation according to claim 1, further comprising a water-permeable material.