JPH0326741B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a method for using temporary concrete to stop water when building a foundation for a main structure, when the foundation is located at a location lower than the groundwater level, or located in a river or the sea. This article relates to an underwater foundation construction method that directly constructs a foundation without pouring it.

Conventionally, when building the foundation of the main structure in the ground in places where the groundwater level is high and the hydraulic conductivity is large, making it difficult to change the water, temporary construction to stop water was used, for example, as shown in Figures 1 and 2. Concrete 1 was placed and dry-up (in the figure, 2 is the groundwater level,
3 shows the earth retaining steel sheet pile). That is, first, as shown in FIG. 1, an excavation space surrounded by earth retaining steel sheet piles 3 is created, and temporary concrete 1 is placed at the bottom in the presence of spring water 4 within this excavation space. Normally, the purpose of this temporary concrete 1 is to stop water, so reinforcement is not particularly required. Next, after this concrete 1 has hardened and has a water-stopping function, water 4 is dry-upped, and as shown in FIG. 2, substructures 5 and 6 with reinforced reinforcement are constructed under dry-up.

However, such conventional temporary concrete 1
The construction method of installing a water stop requires a large amount of concrete to counteract the pumping pressure that is applied under the concrete, and the excavation depth is therefore deep. Therefore, not only does the amount of excavation increase, but also a large area of earth-retaining steel sheet piles 3 is required, the construction period and construction cost also increase due to the temporary concrete pouring.

The purpose of the present invention is to solve the problems of the conventional underwater foundation construction method.
Reinforcing bars for foundation construction are assembled above the water surface, and the assembled rebar structure is lowered into the water and set at the concrete placement position.Then, a thickening agent is added to suppress material separation underwater, so that it does not harden yet. The present invention provides an underwater foundation construction method characterized by pouring concrete into the underwater pouring position.

The construction method of the present invention will be specifically explained below with reference to the drawings.

Figures 3 to 10 show the steps of the construction method of the present invention in order, taking as an example the case where the foundation of the main structure to be constructed is to be built in the ground with a high groundwater level.

(1) Support pile and temporary pile driving process...Figure 3.

If the weight of the building structure is insufficient to compensate for the buoyancy that acts on the building structure during dry-up, if the supporting capacity of the ground is insufficient for the future weight of the building structure, or if there is a risk of future subsidence causing problems, etc. In this step, the support pile 10 is driven. In addition, temporary piles will be driven if necessary for the construction work. Temporary piles can be replaced with support piles. 2 indicates the groundwater level.

(2) Excavation process...Figure 4.

Excavate only the amount necessary to construct the frame.
In other words, unlike in the past, excavation is not carried out for the temporary concrete for waterproofing, but only for the construction of the frame. In this case, if the water level cannot be lowered even after drainage, excavation is carried out with water 4 still present.
11 indicates an excavating machine.

(3) Process of driving steel sheet piles, leveling the excavated surface, and assembling reinforcing bars...Figure 5.

(A) Steel sheet pile driving process If the steel sheet pile 12 can be driven from the ground surface, it may be driven from the ground surface before the above-mentioned excavation process. In this case, it functions as a retaining wall. If the steel sheet pile 12 cannot be driven from the ground surface because of boulders or other obstacles underground, the obstruction is excavated as shown in FIG. 5 before the steel sheet pile 12 is driven.

This steel sheet pile 12 serves as a water-stop wall during dry-up and also serves as a formwork for concrete.
Therefore, the face pieces are constructed so that no gaps are formed between them. However, this steel sheet pile 12 only needs to have sufficient strength to receive the lateral pressure of concrete and the water pressure during dry-up, and there is little risk of boiling or heaving, so the penetration length is smaller than that of a normal cofferdam. It's good.

(b) Excavation surface leveling process: Put chestnut stone or crushed stone 13 on the bottom of the excavation,
Level the surface.

(c) Reinforcing bar assembly process Reinforcing bars are assembled under hanging materials substantially directly above the frame to be constructed and in the air above the water surface. More specifically, the PC
A hypothetical beam 15 is formed by a hanging member 14 such as a steel rod.
A steel frame 16 is suspended above the water surface via the steel frame 16, and reinforcing bars 17 are assembled using the steel frame 16 as a workbench. The steel frame 16 has a truss structure when the span is large. This steel frame 16 is used as an aerial platform for assembling reinforcing bars, but will later be embedded in concrete together with reinforcing bars 17. Therefore, depending on the shape of the concrete, water may be introduced into the concrete, which can cause corrosion of reinforcing bars and steel frames, especially when construction is being carried out using groundwater or seawater in coastal areas. In order to reduce the amount of water taken into the steel frame, it is a good idea to make as many holes as possible in this steel frame as long as its strength allows.

In this way, since the reinforcing steel structure for foundation construction is assembled on the water surface, efficiency and precision can be improved compared to when assembling it underwater. In this case, support pile 1
0 can also be used as a rolling prevention material or a receiving material for the temporary beam 15 in order to perform this assembly work stably. A center hole jack 18 is interposed on the hanging member 14 so that the working position can be adjusted and the assembled reinforcing steel structure can be lowered freely.

(4) Installation process of reinforced structures...Figure 6.

Reinforced structure assembled on the water surface (reinforced steel 17 on steel frame 16 used as a workbench for assembling rebar)
(an integral structure made up of bundles of concrete) is lowered into the water and set at the concrete pouring position.
This is done by operating the center hole jack 18 interposed on the hanging material 14 mentioned above. Note that when reinforcing a standing wall or the like, the reinforcing bars for this part may be set underwater in the same way.

(5) Process of cutting pile heads and placing concrete underwater...Figure 7.

As shown in FIG. 7, the unnecessary part of the pile 10 (the upper part unnecessary for supporting the frame) is removed. This is a work to cut out the protruding portion of the pile 10 from the ground, and is mechanically cut underwater. Next, concrete is placed by the pump truck 20, but before that, if sludge or the like has settled at the concrete placement position, it is sucked up by a sand pump. The concrete to be poured is so-called underwater concrete (for example, hydrocrete), which is mixed with a thickening agent to suppress material separation in water and is adjusted to increase fluidity. When using this underwater concrete, it is not necessary to immerse the discharge port of a tremie pipe into the concrete and cast it in the concrete. It can be easily cast using the same recipe (pouring into the casting position from above). In this case, steel sheet pile 12
will be the side formwork. The site is a coastal area,
If the water level fluctuates due to the influence of tides, etc., a through hole is provided in a part of the steel sheet pile 12,
It is preferable that there be no difference in water level between the inner space and the outer space of the steel sheet pile 12. This is to prevent future water leakage from occurring when the underwater concrete has not yet hardened and excessive water pressure creates a water path.

(6) Dry-up process...Figure 8.

The underwater concrete 22 placed in the previous process is
After sufficient curing in water and its strength reaching the required strength, the water in the internal space closed off by the steel sheet piles 12 is discharged. Of course, if a hole has been made in the steel sheet pile 12, this is closed. As a result, the concrete layer 22 and the steel sheet pile 12
A dry space partitioned by

(7) Ordinary concrete pouring process...Figure 9.

In the dry space formed in the previous process, the wall 23
The necessary frame structure is formed by pouring ordinary concrete.

(8) Sheet pile pulling and backfilling process...Figure 10.

The steel sheet pile 12 is pulled out and the area behind the wall 23 is backfilled to complete the construction of the foundation structure.

In this way, according to the present invention, it is possible to construct a large foundation without providing a temporary concrete layer to stop water even in ground with a high groundwater level and high permeability, and the amount of excavation and amount of concrete can be reduced. It is possible to build a strong foundation with a short construction period and low construction costs while reducing construction costs. Furthermore, foundation structures can be constructed in the same manner in rivers and seawater.

[Brief explanation of the drawing]

Figures 1 and 2 are schematic cross-sectional views for explaining the conventional foundation construction method below the groundwater level. Figure 1 is a diagram showing the stage of forming a temporary concrete layer for waterproofing, and Figure 2 is It is a figure which shows the stage of forming a frame on temporary concrete for waterproofing. Also, Figure 3~
FIG. 10 is a schematic sectional view for explaining a series of steps of the underwater foundation construction method of the present invention.
The figure shows the pile driving process, Figure 4 shows the excavation process, Figure 5 shows the reinforcing bar assembly process, Figure 6 shows the reinforcing bar lowering installation process, Figure 7 shows the underwater concrete placement process, and Figure 8 shows the dry-up process. Fig. 9 shows the ordinary concrete casting process, and Fig. 10 shows the backfilling process. 1... Temporary water stop concrete, 2... Groundwater level, 10... Support pile, 11... Excavation machine, 12...
...Steel sheet pile, 13...Chestnut stone, 14...Hanging material, 15
...Temporary beam, 16...Steel frame that will serve as a workbench, 17...
...Reinforcing bar, 18...Center hole jack, 20
...Pump truck, 21...Hose, 22...Underwater concrete, 23...Ordinary concrete.

Claims (1)

[Claims] 1. When constructing a foundation in a place where the concrete placement position is below the water surface, the reinforcing bars for the foundation construction are assembled above the water surface, the assembled reinforcing steel structure is lowered into the water and set at the concrete placement position, and then An underwater foundation construction method characterized by pouring unhardened concrete containing a thickening agent that suppresses material separation underwater at the underwater placement position.