JP3075179B2 - Bridge pier foundation structure and its construction 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 pier foundation structure and a method of constructing the same, and more particularly, to a pier foundation structure suitable for construction in deep water.

[0002]

2. Description of the Related Art A pier foundation structure for constructing a bridge in a sea area, a lake or the like is selected in consideration of various conditions and a foundation structure and a construction method. In particular, when the construction site is a sea area, conditions such as water depth, weather, and sea conditions have a great influence on the construction period and cost of the construction work. Under such conditions, as a method of constructing a pier foundation for shortening the construction period and improving the work environment, an installation caisson construction method in which a caisson shell serving as a pier foundation is precast is known.

[0003] In this method, a pier foundation is directly constructed on a bedrock, and a prefabricated super-large caisson shell is laid down on a seabed that has been excavated and leveled in advance, and the caisson shell is formed into a formwork. Pre-packed concrete is to be used as a pier foundation. According to this method, a large foundation can be built in a relatively short period of time. However, in particular, when a large foundation is to be built at a depth of more than 100 m, for example, the technical problems described below are required. was there.

[0004]

That is, in the installation caisson method, the underwater ground is excavated and leveled before the caisson shell is submerged. In this case, the solid support ground is exposed. However, since the caisson shell is large and the excavation area becomes large, there is a possibility that large-scale and long-term water pollution will occur.

In the installation caisson method, since the caisson shell is manufactured in advance using a dry dock or the like, the construction period can be shortened accordingly. Offshore work that is affected by natural conditions such as
This leads to delays in the construction period. In addition, in the installation caisson method, if the caisson shell is not submerged and solid supporting ground cannot be obtained, the structure and shape of the foundation will be large to secure the supporting force, and the construction cost will be high. Become.

The present invention has been made in view of such conventional problems, and an object thereof is to reduce excavation of underwater ground and offshore work as much as possible even at a large depth. It is another object of the present invention to provide a pier foundation structure and a method for constructing the same, which can achieve a shortened construction period and reduced cost.

[0007]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention relates to a pier foundation structure, wherein a bottom caisson is settled on an underwater ground, and the bottom caisson is penetrated through the bottom caisson to form the underwater ground. A plurality of tower shafts having a lower end partially penetrated and an upper end side extending above the water surface, a hollow annular precast concrete block stacked on an outer periphery of the tower shaft, and connected to an upper end portion of the tower shaft. A top slab and a prestressed steel material whose upper and lower ends are locked between the bottom caisson and the top slab to introduce tension into the block. In addition, as a method of constructing the basic structure having such a configuration, the bottom caisson is towed to a pier construction site, a step of mooring, and the tower shaft is sunk,
A step of penetrating a part of the lower end into the underwater ground, and after installing the top slab on the bottom caisson, using the tower shaft as a guide, the bottom caisson locking the lower end of the prestressed steel material is Submerging on the underwater ground, stacking the blocks on the outer periphery of the tower shaft while penetrating the prestressed steel, tensioning the prestressed steel, and fixing its upper end to the top slab And the process of doing. According to the pier foundation structure and the construction method of the present invention configured as described above, at least the bottom caisson, the tower shaft, the precast concrete block, and the prestressed member can be manufactured in advance, so that the offshore at the construction site can be used. Very little work. In this case, the length of the tower shaft can be arbitrarily extended by adding, and the blocks stacked on the outer periphery can be correspondingly increased, so that it is suitable for construction at a large depth. At the same time, the stability of the foundation structure is further enhanced because, in addition to its own weight, a pull-out frictional resistance between the tower shaft penetrated into the underwater ground can be expected. In addition, since the lower end of the tower shaft penetrates and is fixed in the underwater ground, the excavated area of the underwater ground is reduced, and it is also suitable for construction in a place where a solid supporting ground cannot be obtained. Furthermore, in the method of constructing a substructure according to the present invention, since a part of the lower end of the tower shaft penetrates into the underwater ground in the first step, the bottom caisson is sunk in a stable state when the bottom caisson is sunk using the tower shaft as a guide. By having the tower shaft support the top slab, the subsequent steps can be performed in a stable state, and the top slab supported by the tower shaft can be used as a work scaffold. The tower shafts can be connected to each other by a connecting member installed at an intermediate portion thereof, and when this configuration is adopted, the integration between the tower shafts is increased, and the tower shaft is suitable as a structure for deeper depth. Become.

[0008]

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 to 5 show one embodiment of a pier foundation structure according to the present invention. The pier foundation structure 10 shown in FIG. 1 includes a bottom caisson 12, a tower shaft 14, a block 16 made of precast concrete, a top slab 18, a prestressed steel member 20, and an intermediate connecting member 21.

Each component of the pier foundation structure 10 is manufactured in advance in a dry dock or the like close to the installation site in a divided state as necessary. As shown in FIG. 2, the bottom caisson 12 is formed in a shape having a substantially square plane, and includes an upper plate 12a, a lower plate 12b, and a side plate 12c.
And four hollow cylindrical portions 12d. Upper plate 1
The 2a and the lower plate 12b are fixed to the annular side plate 12c at an interval in the vertical direction, and a hollow portion 12e is provided inside by this structure.

The cylindrical member 12d is a member through which the tower shaft 14 is inserted.
The upper and lower plates 12a and 12b are arranged at the four corners so as to penetrate therethrough. The lower end of the side plate 12c is
b, and the protruding portion forms a skirt portion 12f of the bottom caisson 12. In this embodiment, the bottom caisson 12 submerged in the seabed ground 22 is:
The skirt portion 12f is formed on the surface ground 22 of the seabed ground 22.
It is installed so as to penetrate into a.

When the bottom caisson 12 is installed, the hollow portion 12e is filled with a ballast 24 for sinking. When the skirt portion 12f penetrates into the surface ground 22a, a negative pressure is applied to the inside of the skirt portion 12f by using a suction pipe (not shown) provided on the lower plate 12b, and suction of sediment by the negative pressure is performed. This is performed by the action and the sinking action of the bottom caisson 12 due to its own weight.

When the skirt portion 12f of the bottom caisson 12 reaches a predetermined position, mortar grout 26 is injected into the skirt portion 12f. Tower shaft 14
Are inserted into the cylindrical member 12d of the bottom caisson 12 and are installed so as to penetrate the bottom caisson 12. In this embodiment, four are used. A steel pipe having a circular cross section, which is divided into a plurality, is connected at the construction site of the pier foundation structure 10 so as to have a predetermined length.

A blind lid 14a is provided at the tip end of each tower shaft 14, as shown in FIG.
Are respectively fixed, and a plurality of suction pipes 14b are penetrated through the blind lid 14a. The tower shaft 14 is filled with water when sinking, and a part of the lower end side of each tower shaft 14 generates a negative pressure by the suction pipe 14b to penetrate the surface ground 22a of the seabed ground 22. Then, it penetrates into the seabed ground 22 so that its tip reaches the support ground 22b.

Precast concrete block 1
In this embodiment, 6 is formed in a hollow annular shape using high-strength concrete and reinforcing steel, and is fitted and stacked on the outer periphery of each tower shaft 14. In each block 16,
Although not shown, a plurality of holes penetrating the thickness portion in the vertical direction are formed, and the prestressing steel materials 20 are inserted into the holes when they are stacked.

The top slab 18 is formed so as to be connected to the upper end side of the tower shaft 14. In this embodiment, the top slab 18 is formed to be similar in plan shape to the bottom caisson 12, and has an upper plate 18a and a lower plate 18a. It has a plate 18b, a side plate 18c, and a cylindrical member 18d. Upper and lower plates 18a, 18b
Are fixed to the side plate 18c at intervals in the vertical direction, are made of reinforced concrete with internal reinforcement, and are constructed either entirely at the construction site or only the outer shell with a dry dock. It is constructed by casting, towing to the site, and then placing concrete in the middle.

At the four corners of the top slab 18, cylindrical members 18d for inserting the block 16 installed on the outer periphery of the tower shaft 14 are embedded. Intermediate connecting member 21
Is manufactured in advance in a dry dock, in which four tower shafts 14 are interconnected at an intermediate position in the longitudinal axis direction to enhance their integrity. In this embodiment, The top slab 18 is formed in substantially the same planar shape as the top slab 18, and includes an upper plate 21a, a lower plate 21b, and a side plate 21c.
And a cylindrical member 21d. Upper and lower plates 18a,
18b is fixed to the annular side plate 18c at intervals in the vertical direction, and has a hollow portion 21e formed therein.

When the intermediate member 21 is installed, the hollow portion 2
The ballast 24 is filled in 1e. The cylindrical member 21 embedded in the intermediate member 21 is open at both ends and has an inner diameter slightly larger than the outer diameter of the block 16. In addition, the presence or absence of the intermediate member 21 can be selected depending on the construction depth of the pier foundation structure 10, and may be installed not only at one place but also at a plurality of places along the depth direction.

One end of the prestressed steel member 20 is fixed to the upper plate 12 a of the bottom caisson 12, and the other end side is a cylindrical member of a plurality of blocks 16 and an intermediate connecting member 21 stacked on the outer periphery of the tower shaft 14. The fixing plate 1 is extended upward so as to penetrate through the fixing plate 1 d and penetrates through the fixing plate 1.
The upper end is fixedly fixed to the upper plate 18a of the top slab 18 via 8e.

The tower shaft 14 and each block 1
6 and the gap between the blocks 16 are integrated with each other by injecting high-fluid concrete or the like from the upper side while prestress is being introduced. Next, a method of constructing the pier foundation structure 10 configured as described above will be described with reference to FIGS. In constructing the pier foundation structure 10, first, as shown in FIG. 6, the bottom caisson 12 is manufactured in a dry dock 28 close to the construction site. When manufacturing the bottom caisson 12, the lower end side of the prestressed steel material 20 is fixed to the upper plate 12a. In parallel with the production of such a bottom caisson 12, excavation and leveling work of the subsidence site are performed.

The fixing position of the prestressed steel material 20 is on the outer peripheral side of the cylindrical member 12d, is disposed so as to surround the cylindrical member 12d, and is used in a state where the required length is divided. The lower end of the tower shaft 14 is inserted into the cylindrical member 12d of the bottom caisson 12, and the shaft 14 is temporarily fixed to the prestressed steel material 20, for example. In this case, the tower shaft 14 having a necessary length divided is used.

When the production of the bottom caisson 12 and the temporary fixing of the tower shaft 14 are completed, the caisson is towed to a submerging site and transported to the construction site of the pier foundation structure 10 as shown in FIG. In this case, when the buoyancy of the bottom caisson 12 is insufficient with only the hollow portion 12e, the airbag 30 may be arranged in the skirt portion 12f as necessary.

In this embodiment, the bottom caisson 12
The tower shaft 14 and the prestressed steel material 20 are locked and the prestressed steel material 20 is locked, and the tower is towed to the construction site. However, the tower shaft 14 and the prestressed steel material 20 are temporarily fixed to the bottom caisson 12. There is no need to fix them, and they may be individually transported to the construction site. When the bottom caisson 12 is towed to the construction site, as shown in FIG. 8, the tower shaft 14 is sunk while the bottom caisson 12 is lifted up by being anchored to the seabed ground 22 by the mooring cable 32. When submerging the tower shaft 14,
This is performed by injecting seawater into the inside of the tower shaft 14 using the cylindrical member 12d of the bottom caisson 12 as a guide. In this case, the tower shaft 14 uses the bottom caisson 12 as a work scaffold, and the subsidence work is performed while successively extending.

When a predetermined number of pipes are added and the tip of the tower shaft 14 reaches the surface layer 22a of the seabed 22, a suction device is connected to the suction pipe 14b, and the tip side of the shaft 14 separated by the blind lid 12a. To create a negative pressure. When such a negative pressure is generated, the ground pressure causes the ground soil on the tip end side of the tower shaft 14 to be sucked, and the tower shaft 14 gradually increases due to the weight of the tower shaft 14 and the weight of the injected seawater. And its tip penetrates the surface ground 22a, and the support ground 2
When it reaches 2b, the laying operation ends.

When the subsidence of each tower shaft 14 is completed,
As shown in FIG. 8, the intermediate connecting member 21 is connected to the bottom caisson 12.
Place on top of When placing the intermediate connecting member 21,
The prestressed steel material 20 is positioned so as to pass through the cylindrical member 21d. When the placement of the intermediate connecting member 21 is completed, the bottom caisson 12 is laid down. When submerging the bottom caisson 12, the tower shaft 14
With the air bag 30 as a guide, the crushed stones and seawater are filled as a ballast 24 in the hollow portion 12e, water is injected into the hollow portion 12e, a jack is mounted on the prestressed steel material 20, and the attitude is controlled by operating the jack. While being jacked down.

The work in this case is performed on the floating intermediate connecting member 21. When the bottom caisson 12 is laid down, the mooring line 32 is released, but the mooring line 32 is locked to the intermediate connecting member 21. When the bottom caisson 12 has landed on the seabed ground 22, as shown in FIG. 9, as in the case of the tower shaft 14, a negative pressure is applied to the skirt portion 12f. The tip of 12f is made to penetrate into the surface ground 22a. When the laying of the bottom caisson 12 is completed, as shown in FIG. 10, the work of stacking the precast concrete blocks 16 is performed.

Precast concrete block 16
Is manufactured in advance in a factory, and is levitated and transported to the construction site of the basic structure 10 by inserting an airbag 30 therein. When the blocks 16 are stacked on the outer periphery of the tower shaft 14, the intermediate connecting members 21
Is used as a work scaffold and the prestressed steel material 20
This is done with a guide. When a predetermined number of blocks 16 are stacked on the outer periphery of each tower shaft 14,
The stacking operation of the block 16 is temporarily stopped, and the intermediate connecting member 2 is stopped.
The construction of the top slab 18 on 1 is performed.

The top slab 18 may be constructed at a construction site, or a shell portion may be manufactured in advance by a dry dock 28 and towed to the site. In the case of this embodiment, when the top slab 18 is constructed, since the intermediate connecting member 21 has substantially the same shape, the intermediate connecting member 21 may be constructed or placed so as to overlap the intermediate connecting member 21. When the construction or placement of the top slab 18 is completed, the intermediate connecting member 21 is laid down.

The intermediate connecting member 21 is laid down in the bottom caisson 1.
As in the case of 2, the crushed stone and seawater are ballasted in the hollow portion 21e.
In Step 4, filling and pouring water, mounting a jack on the prestressed steel material 20, and operating the jack to lower the jack while controlling the posture. When the intermediate connecting member 21 is lowered to a predetermined position, the fixing of the intermediate connecting member 21 and the block 16 is performed.

For this fixing, for example, bolt connection by diving work can be selected. When the fixing of the intermediate connecting member 21 is completed, the stacking work of the blocks 16 is performed again using the top slab 18 as a work scaffold. And
When the stacking of the blocks 16 is completed, the grout 26 is filled in the skirt portion 12f of the bottom caisson 12 to reinforce the supporting force.

Next, the prestressed steel materials 20 are sequentially tensioned to integrate the stacked blocks 16 with each other.
The upper end of the prestressed steel material 20 is attached to the upper plate 1 of the top slab 18.
8a. Then, after this, block 16
The space between the tower shaft 14 and high-flow concrete. When the two are integrated, the pier foundation structure 10 shown in FIG. 1 is completed.

According to the pier foundation structure 10 and the method of constructing the pier foundation structure 10 as described above, at least the bottom caisson 12, the tower shaft 14, the precast concrete block 16, and the prestress member 20 can be manufactured in advance. Therefore, the offshore work at the construction site is extremely reduced, and the work that is influenced by weather and sea conditions is reduced, so that the construction period can be shortened.

In this case, the length of the tower shaft 14 is
Can be extended arbitrarily by adding,
Since the blocks 16 stacked on the outer periphery can be correspondingly increased, the tower shaft 14 which is suitable for construction at a large depth and which is located in the underwater portion is
Since the intervals are provided, the influence of the acting wave force can be reduced.

In the construction method, in particular, the lower end of the tower shaft 14 penetrates so as to reach the support ground 22b in the first step, so that the tower shaft 14 supports the intermediate connecting member 21 and the top slab 18. , Block 1
6 can be performed in a stable state.
Further, in the case of the present embodiment, since the lower end of the tower shaft 14 penetrates and is fixed to the support ground 22b in the seabed ground 22, the excavated area of the seabed ground 22 is reduced, and a solid support ground is obtained. In addition to being suitable for construction in places where there is not, the skirt portion 12f of the bottom caisson 12 also penetrates into the surface ground 22a, so that the foundation structure 10 comes into contact with the ground 22a, 22b in addition to the stability due to its own weight. Extrusion frictional resistance can be expected in the part where it is, and stability is increased.

Further, since the tower shafts 14 are connected to each other by the connecting member 21 installed at an intermediate portion thereof, the integration between the tower shafts 14 is increased, and the tower shaft 14 is suitable as a structure for a larger depth. . In the above embodiment, the case where a steel pipe having a circular cross section is used for the tower shaft 14 is illustrated. However, the present invention is not limited to this. For example, a steel pipe having a square cross section may be used. Good.

[0035]

As described above in detail in the embodiments,
According to the pier foundation structure and the construction method of the present invention, the following effects can be obtained. Excavation of underwater ground is less than the conventional caisson method, so that water pollution caused by excavation and leveling can be extremely reduced. Most of the substructure can be manufactured with dry docks, greatly reducing offshore work, reducing the effects of weather and sea conditions, shortening construction time and reducing construction costs. In constructing the basic structure, the bottom caisson and the like can be effectively used as a work scaffold, and there is no need to set concrete on the sea or install a large-scale temporary yard, and work can be performed stably.

[Brief description of the drawings]

FIG. 1 is a half sectional explanatory view showing one embodiment of a pier foundation structure according to the present invention.

FIG. 2 is a plan view of FIG.

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

FIG. 4 is an enlarged view of a portion B in FIG. 1;

FIG. 5 is an enlarged view of a portion C in FIG. 1;

FIG. 6 is an explanatory half-sectional view of a first step showing one embodiment of a method for constructing a pier foundation structure according to the present invention.

FIG. 7 is an explanatory half-sectional view of a step performed subsequent to the step of FIG. 6;

8 is an explanatory half-sectional view of a step performed subsequent to the step of FIG. 7;

9 is a half sectional explanatory view of a step performed subsequent to the step of FIG. 8;

FIG. 10 is an explanatory half-sectional view of a step performed subsequent to the step of FIG. 9;

11 is an explanatory half-sectional view of a step performed subsequent to the step of FIG. 10;

FIG. 12 is an explanatory half-sectional view of a step performed subsequent to the step of FIG. 11;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Bridge pier foundation structure 12 Bottom caisson 12d Cylindrical member 12f Skirt part 14 Tower shaft 16 Block 18 Top slab 20 Prestressed steel material 21 Intermediate connecting material 22 Submarine ground 22a Surface ground 22b Support ground

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-50-25011 (JP, A) JP-A-6-341112 (JP, A) JP-B-48-6891 (JP, B1) (58) Survey Field (Int. Cl. ⁷ , DB name) E02D 27/32 E02D 23/00 E01D 29/02

Claims (3)

(57) [Claims] 1. A bottom caisson that is landed on an underwater ground, a plurality of tower shafts penetrating the bottom caisson, a part of a lower end penetrating into the underwater ground, and an upper end extending to above the water surface. A hollow annular precast concrete block stacked around the outer circumference of the tower shaft,
A top slab connected to an upper end of the tower shaft, and a prestressed steel material whose upper and lower ends are locked between the bottom caisson and the top slab to introduce tension into the block. Pier foundation structure. 2. The pier foundation structure according to claim 1, wherein the tower shafts are connected to each other by a connecting member installed at an intermediate portion thereof. 3. A bottom caisson that is landed on the underwater ground, a plurality of tower shafts penetrating through the bottom caisson, a part of a lower end of which penetrates into the underwater ground, and an upper end extending to the surface of the water. A hollow annular precast concrete block stacked around the outer circumference of the tower shaft,
A pier foundation structure comprising a top slab connected to the upper end of the tower shaft, and a prestressed steel material whose upper and lower ends are locked between the bottom caisson and the top slab to introduce tension into the block. A method of towing the bottom caisson to a pier construction site and mooring; submerging the tower shaft and partially penetrating a lower end of the tower shaft into the underwater ground; After placing the slab on the bottom caisson,
Using the tower shaft as a guide, submerging the bottom caisson holding the lower end of the prestressed steel material on the underwater ground; stacking the blocks on the outer periphery of the tower shaft while penetrating the prestressed steel material A method of constructing a pier foundation, comprising: a step of installing; and a step of tensioning the prestressed steel material and fixing an upper end thereof to the top slab.