JP2002121754A - Method for constructing underwater foundation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To rapidly submerge a foundation. SOLUTION: In a construction method for an underwater foundation, a plurality of vertical drain members 22 are driven into the water bed ground A at a scheduled place of submergence of a caisson skeleton until the vertical drain members reach a load bearing layer. A filter layer 24 for communicating upper end sides of the vertical drain members 22 with each other is installed. Next, the caisson skeleton 10 is submerged to allow the tip of the skirt part 18 penetrated into the water bed ground A. After grouting 28 is poured between the filter layer 24 and a bottom slab part 16, water in the water bed ground A is discharged from a water collection and discharge facility 20 provided on the caisson skeleton 10 in advance via the vertical drain members 22 and the filter layer 24, and the suction load is applied to the caisson skeleton 10.

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 which can be used as a seawall, a breakwater, and the like.

[0002]

2. Description of the Related Art When constructing a foundation underwater, in the case of a pile foundation, mechanical force such as impact or vibration can be used as a pushing force. However, if the soft layer is thicker than the ground support layer and the depth of the support layer is deep at the site where the foundation is to be constructed, the pile driving method using impact or vibration, the compaction and solidification method, etc. Costly and time consuming.

Therefore, as a construction method adopted when the depth to the support layer is large, a suction foundation construction method in which a caisson body having a skirt portion is sunk in the underwater ground by utilizing a pressure difference (suction). The construction method called is attracting attention recently.

FIG. 5 shows an example of such a suction foundation method. In the suction foundation method shown in FIG. 1, the caisson frame 1 includes a cylindrical main body 2 and a skirt 3 provided at the lower end of the main body 2.

[0005] A pumping passage 4 is formed through the main body 2. When constructing an underwater foundation, the caisson skeleton 1
Is submerged in the underwater ground 5.

At this time, the lower end side of the skirt portion 3 penetrates into the water bottom ground 5 to prevent the inflow of water, and in this state, the water in the skirt portion 3 is removed via the water pumping passage 4. The pressure in the skirt portion 3 is reduced by the above, a pressure difference is generated between the inside and the outside of the skirt portion 3, a suction load is applied, and the caisson body 1 is sunk to a predetermined depth of the underwater ground 5 using the suction load. .

The construction method of such an underwater foundation is relatively easy to construct, and the caisson frame 1 sufficiently buried in the underwater ground 5 has a remarkable resistance to sliding, falling, supporting force, pulling out and sinking. It has the advantage of increasing.

However, such a conventional method of constructing an underwater foundation has the following technical problems.

[0009]

That is, in the conventional suction foundation method, water in the skirt portion 3 is removed from the pumping passage 4.
Drained through the ground, but the ground 5 surrounded by the skirt 3
The water inside takes time to reach the pumping passage 4,
As a result, it takes time to sink the entire foundation to a predetermined depth.

Further, when water in the skirt portion 3 is removed through the pumping passage 4, unevenness occurs in the drainage state between the central portion and the peripheral portion in the skirt portion 3, and such unevenness occurs. When drainage is performed, the bearing capacity becomes unbalanced, causing the foundation to tilt.

The present invention has been made in view of such a conventional problem, and an object of the present invention is to provide a method of constructing an underwater foundation in which foundation can be quickly settled and drainage can be uniformly performed. Is to provide.

[0012]

In order to achieve the above object, the present invention provides a caisson body having a skirt portion extending below a bottom slab portion, which is installed in a water bottom ground by applying a suction load. In the method of constructing an underwater foundation, a step of placing a plurality of vertical drain materials in the underwater ground at a place where the caisson skeleton is to be laid, and laying and forming a filter layer for communicating between upper end sides of the vertical drain materials. And laying down the caisson skeleton,
A step of penetrating the tip of the skirt portion into the underwater ground, a step of injecting a grout material between the filter layer and the bottom slab, and a step of interposing the vertical drain material and the filter layer to form the underwater ground. The water therein is drained by a collecting / draining facility provided in advance in the caisson skeleton to apply a suction load to the caisson skeleton. According to the construction method of the underwater foundation constructed in this way, the caisson body will
A step of laying a plurality of vertical drain materials and a step of laying and forming a filter layer communicating between upper end sides of the vertical drain materials, through the vertical drain material and the filter layer, water in the underwater ground, Since the water is drained by the collection and drainage facilities provided in advance in the caisson frame,
Water in the ground surrounded by the skirt portion can be quickly removed. For this reason, the compaction of the ground in the part surrounded by the skirt portion and the ground improvement can be performed at an early stage,
The caisson skeleton can be sunk quickly to a predetermined depth. In addition, drainage by the drainage system is performed by laying and forming a filter layer that communicates between the upper ends of the vertical drain material, and the drainage is performed through the filter layer. . The tip of the skirt portion penetrating into the underwater ground is located at a position separated upward from a support layer of the underwater ground, and can be in a floating foundation state. The vertical drain material can be cast so that its lower end is located near the support layer.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 to FIG. 4 show an embodiment of the construction method of an underwater foundation according to the present invention.

In the construction method of the underwater foundation of this embodiment, FIG.
The underwater foundation shown in FIG. 1 is constructed, and the underwater foundation includes a caisson frame 10. Caisson building 10
Has a cylindrical main body 12 that is open at the upper and lower ends, an upper plate portion 14 and a bottom plate portion 16 integrally provided on the lower end side of the main body 12 with an interval in the vertical direction.

The upper plate portion 14 and the bottom plate portion 16 are formed in a disk shape of the same size extending in the horizontal direction, and a cylindrical side wall portion 17 is integrally formed on an outer peripheral edge thereof. At the lower end of the side wall portion 17, a cylindrical skirt portion 18 of the same diameter is integrally formed so as to extend downward, and the lower end of the skirt portion 18 extends below the lower surface of the bottom plate portion 16. I have.

The caisson body 10 is provided in advance with a drainage system 20 used for applying a suction load. The collecting and draining facility 20 includes a pump 20a, a pump 20b, a pump 20c, and a drain 20d.

The water pump 20a is installed in the main body 12, and a drain pipe 20d, one end of which is connected to the water pump 20a, extends vertically through the main body 12 and extends to the outside.

The pumping pipe 20b has a pump pump 20a at one end.
And the other end is connected to the pumping port 20c.
The water pumping port 20c is formed in the inner peripheral surface of the skirt portion 18 by opening.

The caisson body 10 having such a structure is prepared in advance in a dock or the like, and is towed to a construction site of an underwater foundation. When constructing an underwater foundation using such a caisson body 10, first, as shown in FIG. 1, a vertical drainage material 22 is placed.

The vertical drain member 22 is provided on the bottom A
The lower part of the soft ground layer A2 penetrates through the soft ground layer A2 from above the water bottom A1, and the lower end reaches the support layer A3, and the upper end reaches the water bottom A1 and slightly protrudes upward. It is driven almost vertically inside.

The vertical drain material 22 is, for example, a sand drain compacted with sand, paper or PVC.
It is composed of a drain material, a packed drain material, and the like, and has a function of collecting water in the surrounding soft ground layer B and guiding the water upward.

Such a vertical drain member 22 is
In the submarine ground A at the place where the caisson skeleton 10 is to be submerged, for example, a plurality of pieces are sequentially driven from the water by using a work boat sequentially on lattice points set at predetermined intervals in the front-rear and left-right directions. You.

In this embodiment, the vertical drain material 22 is cast such that the lower end thereof reaches the support layer A3. However, the vertical drain material 22 is
It is not always necessary to drive the lower end to reach the support layer A3, but it is sufficient to drive the lower end to a depth that is located near the support layer A3.

When the placement of the vertical drain material 22 is completed, a step of laying the filter layer 24 shown in FIG. 2 is performed.

As the filter layer 24, for example, a relatively large block-shaped solid such as crushed stone, synthetic resin, or brick having water permeability, or a mixture of these with a small-diameter solid such as sand is used. A predetermined thickness is laid between the upper ends of the vertical drain members 22 slightly projecting on the bottom surface A1 so as to communicate with each other so that water can permeate each other.

The laying range of the filter layer 24 is laid so as to be larger than the laying range of the vertical drain material 22 and slightly larger than the laying area of the caisson frame 10.

When the laying of the filter layer 24 is completed, as shown in FIG. 3, a step of laying down the caisson body 10 towed to the vicinity of the foundation construction site is performed.

When the caisson frame 10 is laid down, for example, in addition to the weight of the caisson frame 10, the inside of the main body 12 and the inside of the compartment 26 defined by the upper plate portion 14, the bottom plate portion 16, and the side wall portion 17 are added. Then, a ballast load such as water is applied to lower the caisson body 10 gradually into the water.

When the tip of the skirt portion 18 reaches the underwater ground A and penetrates to a predetermined depth, as shown in FIG. 4, the filter layer 24 and the lower surface of the bottom plate portion 16 whose outer periphery is surrounded by the skirt portion 18 are formed. Between the grout material 28
Is performed.

The grout material 28 used at this time is, for example, a mortar that hardens in water. When the grout material 28 injected and filled between the filter layer 24 and the lower surface of the bottom plate 16 hardens, the grout material is collected and drained. By driving the pump 20a of the pump 20, the water that the filter layer 24 has is drained from the pumping port 20c.

When the water in the filter layer 24 is removed, the pressure in the portion surrounded by the skirt 18 decreases,
The suction load acts on the upper plate portion 14 and the like, and thereby the caisson frame 10 is gradually settled in the underwater ground A.

On the other hand, when the drainage by the drainage system 20 is continued, the water contained in the soft ground layer A2 is sequentially supplied to the filter layer 24 via the vertical drain material 22 and supplied. The water is subsequently discharged to the outside.

In this case, the soft ground layer A2 on which the vertical drain material 22 is cast is also subjected to the pressure due to the sinking of the caisson frame 10, so that the consolidation is promoted and the soft ground layer A2 is formed by this pressure. The water contained in the belt is pushed to the vertical drain material 22 side, and by maintaining such a state, a synergistic effect between the application of a suction load and the collection and drainage of the vertical drain material 22 causes a soft ground layer. The water in A2 is quickly removed, and the ground in this part can be compacted.

When the tip of the skirt portion 18 has penetrated to a predetermined depth in the underwater ground A, the drainage by the drainage system 20 is terminated, and the construction of the foundation is completed. When the construction method of the present invention is directly used for relatively long structures such as seawalls and breakwaters, for example, the caisson skeletons 10 may be sunk so as to be sequentially connected in the lateral direction.

According to the construction method of the underwater foundation constructed as described above, the vertical drain material 22 is placed on the support layer A in the underwater ground A where the caisson body 10 is to be laid.
3 and a filter layer 24 for communicating between the upper ends of the vertical drain members 22.
And forming a vertical drain material 2
2 and the filter layer 24, the water in the underwater ground A is collected and drained and installed in a caisson body 10 in advance.
As a result, water in the ground surrounded by the skirt portion 18 can be quickly removed.

Further, if water in the ground surrounded by the skirt portion 18 is quickly removed, compaction of the ground surrounded by the skirt portion 18 and improvement of the ground can be performed at an early stage, and the caisson frame 10 can be removed. It can be sunk quickly to a predetermined depth, and a significant improvement in construction efficiency is achieved.

In the underwater foundation of this embodiment, in consideration of such effects of compaction of the ground and improvement of the ground, the lower end of the skirt portion 18 is located at a position above the support layer A3 and is a kind of floating. It is the basis.

By the way, in the case of such a floating foundation,
The subsidence of the lower part of the foundation, that is, the subsidence of the lower part of the skirt portion 18 becomes a problem, but in this embodiment, the ground of the lower part of the foundation is positively consolidated in advance by using suction, and the superstructure is loaded. Even if it does not sink.

Therefore, it is not necessary to use an expensive material such as a weight balance in order to promote settlement, unlike a conventional floating foundation, and the time and cost required for on-site work can be reduced also from this point.

Further, the drainage by the drainage system 20 is formed by laying a filter layer 24 communicating between the upper ends of the vertical drain members 22 and through the filter layer 24. Is eliminated, and uniform drainage is performed, whereby inconveniences such as inclination of the caisson body 10 can be reliably avoided.

In the above embodiment, the caisson frame 10
Although the structure in which the upper plate portion 14 and the bottom plate portion 16 are provided has been exemplified, the embodiment of the present invention is not limited to the caisson frame 10 having this structure, and may be a caisson frame having another shape. .

[0042]

As described above in detail, according to the method of constructing an underwater foundation according to the present invention, the foundation can be quickly laid down and the drainage can be uniformly performed.

[Brief description of the drawings]

FIG. 1 is an explanatory sectional view of an initial step of a method for constructing an underwater foundation according to the present invention.

FIG. 2 is an explanatory sectional view of a step performed subsequently to FIG. 1;

FIG. 3 is an explanatory cross-sectional view of a step performed subsequently to FIG. 2;

FIG. 4 is an explanatory cross-sectional view of a step performed subsequently to FIG. 3;

FIG. 5 is an explanatory diagram showing an example of a conventional underwater foundation construction method.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Caisson body 12 Main body 14 Upper plate part 16 Bottom plate part 18 Skirt part 20 Collection and drainage equipment 22 Vertical drain material 24 Filter layer 28 Grout material A Underwater ground A1 Water bottom A2 Soft ground layer A3 Support layer

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2D018 BA12 2D046 DA61

Claims (3)

[Claims] 1. A method of constructing an underwater foundation in which a suction load is applied to a caisson skeleton having a skirt portion extending below a bottom slab portion to install the caisson skeleton in a submarine ground. In the underwater ground,
A step of laying a plurality of vertical drain materials; a step of laying and forming a filter layer that communicates between upper ends of the vertical drain materials; and a step of laying down the caisson body to form a tip of the skirt portion in the underwater ground. And a step of injecting a grout material between the filter layer and the bottom slab portion; and, through the vertical drain material and the filter layer, water in the underwater ground is previously supplied to the caisson body. A method for constructing an underwater foundation, characterized in that drainage is provided by a provided drainage system and a suction load is applied to the caisson body. 2. The skirt portion penetrating into the underwater ground, the tip of the skirt portion is located at a position upwardly separated from a support layer of the underwater ground, and is in a floating foundation state. Construction method for underwater foundations. 3. The method of constructing an underwater foundation according to claim 2, wherein the vertical drain material is cast so that a lower end thereof is located near the support layer.