JP2001311166A - Construction method for underwater foundation structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a construction method exerting less influence on the peripheral sea area and reducing a construction period and facilitating the maintenance work. SOLUTION: A casson frame body 10 has a skirt 12 and a casson body 14 divided from each other. The skirt 12 and the casson body 14 are tugged to a construction site and the skirt 12 is immersed into the underwater ground 24. In this time the skirt is immersed so that the cylindrical part 18 is positioned in the lower side. The front end is forced to penetrate into the underwater ground 24 to exert a suction load. When the skirt 12 is immersed down to a specified depth, the caisson body 14 is put on the upper slab 16 of the skirt 12. After the caisson body 14 is installed in a specified position of the upper slab 16, a plurality of external cables 22 are set between the upper and lower rings 23, 20 and the skirt 12 and the casson body 14 are fixedly connected from the outside.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of constructing an underwater substructure, and more particularly to a method of constructing an underwater substructure by effectively applying a suction load.

[0002]

2. Description of the Related Art When constructing a foundation structure underwater, in the case of a pile foundation, mechanical force such as impact or vibration can be used as a pushing force. In such a deep water foundation, it is difficult to lay the foundation structure due to such mechanical force.

Therefore, as one of the construction methods of such a deep water substructure, there is a construction method in which a caisson body having a skirt portion is sunk in the underwater ground using a pressure difference (suction).

In this construction method, a skirt portion is provided on the outer periphery of the lower end of a cylindrical caisson body so as to penetrate into the water bottom to prevent the inflow of water, and the tip side of the skirt portion penetrates into the underwater ground. By removing water in the skirt, a pressure difference is generated between the inside and the outside of the skirt, and the caisson body is submerged in the underwater ground.

When an underwater foundation is constructed using such a suction, for example, when the installation depth is large, or when the height of the entire structure including the skirt portion becomes large due to construction restrictions, Conventionally, the following construction method has been used. . A construction method in which the skirt and caisson body are separated and made with a dock, etc., and assembled at the construction site. . A construction method in which a skirt is made in advance in a dock or the like, and in a sea area with sufficient water depth, a caisson body is built offshore above the skirt and then laid on the seabed.

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

[0007]

That is, in the former construction method, the skirt portion and the caisson main body are separated from each other and assembled at the construction site. The part and the caisson body individually resist, which is structurally uneconomical.

In this case, a structure in which the skirt portion and the caisson main body are internally integrated at a joint surface between the two may be considered, but the work becomes complicated because accurate positioning of both is required. At the same time, maintenance becomes difficult.

[0009] On the other hand, in the latter construction method, the caisson body is constructed offshore above the skirt portion in a sea area with a sufficient water depth, but the offshore construction is easily affected by weather, sea conditions, and the like. Is not only a delay in the construction period,
It may also affect fisheries in the surrounding waters.

The present invention has been made in view of such conventional problems, and has as its object to reduce the impact on the surrounding sea area and to shorten the construction period.
An object of the present invention is to provide a construction method of an underwater substructure that is easy to maintain and maintain.

[0011]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention relates to a method of constructing an underwater substructure laid underwater by applying a suction load to a caisson frame which is a main component of the underwater substructure. Is divided into a skirt portion whose tip side penetrates into the underwater ground and a caisson main body connected to the upper side thereof, applying a suction load to the skirt portion, and after penetrating the tip end side into the underwater ground and installing it. Then, the caisson main body is placed on the upper side of the skirt portion, and thereafter, the skirt portion and the caisson main body are connected and fixed to each other on the outside. According to the construction method of the underwater substructure constructed as described above, the caisson body is separated into the skirt portion and the caisson body,
There is no need for offshore construction, even if the installation depth is deep and the skirt height is large. Further, since the caisson body is separated into the skirt portion and the caisson main body, these can be simultaneously manufactured by a dock or the like, thereby shortening the construction period. Further, a suction load is applied to the skirt portion, and the tip side of the caisson body is placed on the upper side of the skirt portion after penetrating and installing the tip side into the underwater ground. After that, the skirt portion and the caisson body are connected to the outer side. , The skirt portion and the caisson body can be integrated to resist external force, and the connection and fixing portion can be easily maintained. In the construction method of the present invention, the connecting and fixing means of the skirt portion and the caisson main body, one end side is fixed to the skirt portion,
The other end can be composed of a plurality of external cables fixed to the caisson body by introducing a prestressing force. According to this configuration, since the prestress is introduced into the external cable, it is possible to flexibly cope with the external force by the prestress force. Further, according to this configuration, the extension and replacement of the external cable can be easily performed. Further, in the present invention, the outer cables can be installed obliquely so as to be oblique to each other. According to this configuration, the prestressing force of the outer cable installed obliquely and obliquely can be applied not only in the vertical direction but also in the circumferential direction, so that the in-plane shear strength can be increased.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. 1 and 2 show an embodiment of a construction method of an underwater substructure according to the present invention.

As shown in FIG. 2, the underwater substructure shown in FIG. 1 includes a caisson frame 10 serving as a main body of the underwater substructure.
Is made of reinforced concrete, for example, and has a skirt portion 12 and a caisson body 14, which are divided.

The skirt portion 12 of the present embodiment is entirely formed in a substantially inverted concave shape having an open lower end, and has a disk-shaped upper plate 16 having a predetermined thickness, and is integrally formed on the outer peripheral edge of the upper plate 16. It has a formed cylindrical portion 18 and a partition wall portion 19 that partitions the interior defined by the cylindrical portion 18 into a plurality.

An annular lower ring 20 having a similar shape to the outer circumference of the upper plate 16 and being concentric is fixedly supported on the disk-shaped upper plate 16. The lower ring 20 has a flat lower surface separated from the upper surface of the upper plate 16 by a predetermined distance.
It is supported to face this.

After the skirt portion 12 and the caisson main body 14 are installed on the lower ring 20, the lower end of the outer cable 22 for connecting and fixing the two is locked and fixed, as will be described later.

The caisson body 14 is formed in a bottomed cylindrical shape having a diameter smaller than that of the upper plate 16 of the skirt portion 12, and has an open upper end. On the upper side surface of the caisson body 14, an annular upper ring 23 is fixed.

The upper ring 23 has an inner diameter larger than the diameter of the caisson body 14 and
Is fixedly supported so as to protrude outward from the outer peripheral surface of the skirt portion 12 and the caisson body 1 as described later.
After installing the cable 4, the upper end of the outer cable 22 for connecting and fixing the two is locked and fixed.

The upper and lower rings 20, 23 are
The outer cable 22 need not be formed in an annular shape, but may be in a projecting shape to which the outer cable 22 can be fixed.

The skirt portion 12 and the caisson body 14 having such shapes are simultaneously constructed in a dock or the like near the construction site, and when the construction is completed, the skirt portion 12 and the caisson body 14 are towed to the construction site. Skirt part 12 and caisson body 1 to construction site
When the tow 4 is towed, first, as shown in FIG. 1, the skirt portion 12 is sunk and installed in the underwater ground 24.

When the skirt portion 12 is laid down, the skirt portion 12 is laid down so that the tip ends of the cylindrical portion 18 and the partition wall portion 19 are located downward, and the tip ends are penetrated into the underwater ground 24.
Apply suction load. In order to apply this suction load, a plurality of pipes 26 are installed so as to penetrate the upper plate 16 of the skirt 12 as shown in FIG.

Then, via the pipe 26, the cylindrical portion 18
Eliminate the water inside and reduce the internal pressure. When the pressure in the cylindrical portion 18 is reduced, the pressure difference between the water depth and the upper plate 16 increases.
Acting upward, such a suction load allows the skirt portion 12 to be gradually submerged in the underwater ground 24.

When the skirt 12 is sunk to a predetermined depth, the pipe 26 is removed to remove the suction load, and the caisson body 14 is placed on the upper plate 16 of the skirt 12 as shown in FIG. .

When the caisson body 14 is placed at a predetermined position on the upper plate 16, the upper and lower rings 23 and 20 oppose each other at an interval in the vertical direction.
Attach a plurality of outer cables 22 between the skirts 1
2 and the caisson body 14 are connected and fixed from the outside.

The outer cable 22 has a lower ring 20 at the lower end.
The upper end side is fixed to the upper ring 23. In the case of the present embodiment, the plurality of outer cables 22 surround the outer periphery of the caisson body 14 at predetermined intervals in the circumferential direction. Are arranged so as to be parallel to the axial direction of the caisson body 14.

In the case of the present embodiment, a prestressing force is introduced into each of the outer cables 22, and the upper end is fixed to the upper ring 23 so as to maintain the introduced prestressing force. .

As a configuration for introducing and maintaining such a prestressing force, for example, a nut is attached to the upper end of the outer cable 22 while the upper end of the outer cable 22 whose lower end is locked and fixed to the lower ring 20 is pulled by a jack. Or a wedge cone, and that portion may be fixed to the upper ring 23.

When a prestressing force is applied to each outer cable 22 to fix the upper and lower ends thereof, the skirt portion 12 and the caisson body 14 are integrated, and the construction of the underwater substructure is completed.

The portion indicated by reference numeral 28 in FIG. 2 is a filling mortar for filling the cylindrical portion 18 of the skirt portion 12 submerged in the underwater ground 24 by applying a suction load. 28 is applied at an appropriate time after the skirt portion 12 is penetrated.

According to the construction method of the underwater substructure carried out as described above, the caisson frame 10 is separated into the skirt portion 12 and the caisson main body 14, so that the caisson body 10 is separated from the skirt 12 even if the installation water depth is deep. Even if the height gets bigger,
There is no need to build offshore.

The caisson frame 10 is connected to the skirt 12
And the caisson main body 14, so that they can be manufactured simultaneously by a dock or the like, and the construction period can be shortened.

By eliminating the need for such offshore construction and shortening the construction period, the influence on the surrounding sea area of the construction site can be extremely reduced.

Further, a suction load is applied to the skirt portion 12 so that the tip side of the skirt portion 12 penetrates into the underwater ground, and then the caisson main body 14 is placed on the upper side of the skirt portion 12. Since the caisson body 14 is connected and fixed to the outside on the outside,
The skirt portion 12 and the caisson body 14 can be integrated and opposed to each other, and the connection and fixing between them can be performed externally, so that the maintenance of the connection and fixing portion can be easily performed.

In the case of this embodiment, the skirt 1
The connecting and fixing means for connecting the cable 2 to the caisson main body 14 includes an outer cable 22 having one end fixed to the skirt portion 12 and the other end fixed to the caisson main body 14 by introducing a prestressing force.
It consists of.

When a prestress is introduced into the outer cable 22 that integrates the skirt portion 12 and the caisson body 14, the external force can be flexibly dealt with by the introduced prestress force.

Further, since the outer cable 22 of this embodiment is arranged outside the caisson body 14, the extension and replacement of the outer cable 22 can be easily performed. FIG. 3 shows another embodiment of the construction method of the underwater substructure according to the present invention, and the same or corresponding portions as those in the above embodiment include:
The same reference numerals are given and the description is omitted, and only the characteristic points will be described below.

The caisson frame 10 of the underwater substructure shown in FIG.
4 is provided. When constructing the substructure, first, the skirt portion 12 is moved by the suction load to the underwater ground 2.
The caisson main body 14 is placed on the upper side of the caisson.

The connection between the skirt portion 12 and the caisson main body 14 is fixed by connecting the ends of the plurality of outer cables 22a to which the prestressing force is introduced to the skirt portion 12 and the caisson main body 1.
4, respectively.

In this embodiment, a plurality of external cables 2
2a are installed in a state where they are oblique to each other. According to the construction method of the underwater substructure constructed as described above, the following effects can be obtained in addition to the functions and effects of the above embodiment.

When the outer cable 22a is installed obliquely, the prestressing force of the outer cable 22a installed obliquely can be applied not only in the vertical direction but also in the circumferential direction, so that the in-plane shear strength is increased. Can be.

In the above embodiment, the outer cables 22 and 22a for introducing a prestress force for connecting and fixing the skirt portion 12 and the caisson body 14 are exemplified. However, the connecting and fixing means is not limited to this. For example, a cable that does not introduce a prestressing force may be used, or both may be connected and fixed by an anchor or the like.

[0042]

As described above in detail in the embodiments,
According to the construction method of the underwater substructure according to the present invention, the influence on the surrounding sea area is small, and the construction period can be shortened,
Operation and maintenance can be performed easily.

[Brief description of the drawings]

FIG. 1 is an explanatory cross-sectional view of an initial state of construction showing one embodiment of a method of constructing an underwater substructure according to the present invention.

FIG. 2 is an explanatory side view of a step performed subsequent to FIG. 1;

FIG. 3 is an explanatory side view of a construction completion state showing another embodiment of the method of constructing an underwater substructure according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Caisson body 12 Skirt part 14 Caisson main body 16 Upper plate 18 Cylindrical part 20 Lower ring 22 Outer cable 23 Upper ring

Claims (3)

[Claims] In a method of constructing an underwater substructure to be submerged in a submerged ground by applying a suction load, a caisson body serving as a main body of the underwater substructure is provided with a skirt portion whose tip side penetrates into the submerged ground, After dividing into a caisson main body connected to the upper side, applying a suction load to the skirt portion, and penetrating and installing the tip end side in the underwater ground, placing the caisson main body on the upper side of the skirt portion, Thereafter, the skirt portion and the caisson main body are connected and fixed to each other on the outside side. 2. A connection fixing means for connecting the skirt portion and the caisson main body, one end of which is fixed to the skirt portion,
The underwater substructure construction method according to claim 1, wherein the other end comprises a plurality of outer cables fixed to the caisson body by introducing a prestressing force. 3. The construction method of an underwater substructure according to claim 2, wherein the outer cables are installed obliquely so as to be oblique to each other.