JPH0437882B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a method of constructing a deep water cell.

``Prior Art'' Caisson construction method, cell construction method, etc. are known as general construction methods for constructing breakwaters and seawalls.

Among these Shiburi construction methods, the cell method can be further divided into the steel sheet pile cell method and the steel plate cell method, but the common problem with the cell method is that the cells are damaged due to the lateral pressure of the filling earth and sand packed into the cells. Since a large tensile stress is generated in the cell shell in proportion to the diameter and height of the cell, there is a limit to its installation depth. Currently, the limit of cell construction method is approximately 20m.
It is believed that cell construction at deeper water depths is impossible.

"Problems to be Solved by the Invention" In order to solve the above-mentioned drawbacks, the steel plate cell method is used to thicken the steel plate of the cell shell, or the cell shell has a double structure. year number
125512), but making the steel plate thicker would increase its weight and require a special large crane, and the steel plate itself would have to be custom-manufactured, making it impractical from a construction standpoint. I can't think of it,
Further, if the cell shell has a double structure, it becomes difficult to cast the cell shell, and the time required for casting the cell shell also doubles. Therefore, in the case of large water depths, the most commonly used method is to first create a foundation mound with a predetermined height depending on the water depth, and then construct a caisson or cell on top of the foundation mound. has the disadvantage that the foundation mound becomes enormous depending on the water depth.

In addition, procurement of filler soil becomes more difficult as the cell construction site moves further offshore, which also has the drawback of increasing costs.

Therefore, the present invention was made in view of the above-mentioned drawbacks, and provides a method that enables cell construction at deep water points, and a method that easily enables cell filling even in locations where it is difficult to obtain high-quality filling soil. It is intended to provide.

``Means for Solving the Problems'' In accordance with the above object, the structure of the present invention, which is summarized in the above-mentioned claims, is to solve the above-mentioned problems by installing a cell at a construction site, and inside the cell. Filling soil mixed with a hardening material and additives is introduced from the bottom of the pipe using an underwater transport pipe, and the curing start time of the above filling soil is adjusted according to the feeding speed. A technical measure is taken in which the tensile stress generated in the cell shell due to the lateral pressure of the filling earth and sand in the upper unhardened part does not exceed the allowable stress throughout the cell shell. .

``Example'' Next, an example of the present invention will be described below with reference to FIGS. 1 and 2.

The illustrated embodiment is an example in which a steel sheet pile cell 7 with a diameter of 30 m is installed on an already constructed foundation mound 4, and the water depth above the foundation mound 4 is 40 m. In addition, it goes without saying that this steel sheet pile cell 7 may be a steel plate cell formed by forming a steel plate into a cylindrical shape.

First, in this embodiment, the steel sheet pile cells 7 assembled at a base on land (not shown) are placed on a barge (also not shown), transported over the sea, and installed at the installation point on the foundation mound 4 constructed on the seabed 5 as shown in FIG. Work barge 8 shown
Alternatively, the work barge 8 can tow it from the land base to the installation point while floating on the sea. At this time, the buoyancy of the steel sheet pile cell 7 may be obtained by attaching a steel float (not shown) to the steel sheet pile cell 7 in a reusable manner.

Although the work barge 8 will not be described in detail, it is equipped with a gate type crane 12, a residence and control room 13, a hardening material silo 9, a mixing plant 10, a slurry pump, a water content ratio adjusting device 11, and the like.

Then, the steel sheet pile cell 7 is mounted on the foundation mound 4 so as to be held by the work barge 8 at a desired installation point.
will be installed in

Next, an underwater transport pipe 6 typified by what is called a tremie pipe is built into the steel sheet pile cell 7 . The number of underwater transport pipes 6 is determined by the size of the steel sheet pile cell 7, the capacity of the mixing plant 10, and the hardening start time of the filling earth and sand, which will be described later. Then, filling earth and sand mixed with a hardening material and additives are introduced into the steel sheet pile cell 7 from the lowest part thereof using an underwater transport pipe 6.

The hardening materials mentioned above include cement, lime, slag,
A special cement or the like may be used, but any conventionally known hardening material may be used as long as it has early strength when combined with additives. However, considering general sea conditions and rapid construction, the curing time is considered to be about 24 hours, so it is best to select a material that easily meets these conditions. The same applies to the above additives, and any additive may be used as long as it has early strength when combined with the hardening material, but it must have salt resistance, fluidity, and early strength. is desirable.

Furthermore, by adjusting the hardening start time of the filling soil in accordance with the charging speed, the tensile stress generated in the cell shell made of the steel sheet pile cells 7 due to the lateral pressure of the filling soil in the upper unhardened portion can be reduced. The entire cell shell is designed not to exceed an allowable stress level.

Here, the height of the filling soil that satisfies the allowable stress level is calculated from the tensile stress level acting on the cell shell.

Unit volume weight of filling earth and sand: γ (t/m ³ ) Height of filling earth and sand: H (m) Radius of steel sheet pile cell: r (m) Static earth pressure coefficient: Ko (Static earth pressure coefficient is Using the internal friction angle Φ of sand, let Ko = tanΦ.) Assuming Φ = 30°, γ = 1.5t/m ³ , r = 15m, Ko
= approximately 0.6, so if the allowable stress of the cell shell is 1900 kgf/cm ² at the depth H (m) of the filling earth and sand, the allowable tension for a height of 1 m when the thickness of the steel sheet pile cell 7 is 1.27 cm is: 1.27×100×1900≒241(tf).

On the other hand, the tensile stress generated in the cell shell is Since Ko・γ・H・r, H=241/Ko・γ・r≒17.9(m).

In reality, the value of H is determined by the sliding of the cell shell (wave force,
The stability against horizontal movement due to its own weight, etc.), overturning (rotation due to wave force of the cell shell), and shearing (shear failure of the packed earth and sand inside the cell shell) is calculated, and the value is even smaller, but for the sake of calculation, H = 17.9m, if the above-mentioned cell shell was used with the conventional construction method, it would be impossible to construct a cell at a water depth greater than 17.9m, which is the value of H. In the method, as shown in Fig. 1, a steel sheet pile cell 7 is placed on top of a foundation mound 4, and the filling soil in the steel sheet pile cell 7 is divided into a hardened part 3, which is an already hardened part, and a part which is not yet hardened. It is divided into an uncured part 2. Of these two parts, it is the unhardened part 2 that causes tensile stress to be generated in the cell shell due to lateral pressure. Therefore, as long as the height D of the uncured portion 2 does not exceed 17.9 m, the cell shell is safe according to the above calculation. Considering the additional allowable stress during actual construction (calculated as a 1.5 times additional increase in the case of short-term steel structures), the height D of the unhardened portion 2 can be made even higher. It is.

In this way, according to the present invention, the diameter of the steel sheet pile cell 7,
By keeping the height D of the uncured portion 2 within Hm determined by the unit volume weight of the filling sand and the internal friction angle, it becomes possible to construct cells in large water depths.

Using the method described above, the filling operation is continued while keeping the height D of the uncured portion 2 below H=17.9 m in this case, and the filling is completed to the top of the cell. The filling work is carried out using a work barge 8 and a plant on the barge as schematically shown in FIG. It is fed into the bottom of the steel sheet pile cell 7 through the pipe 6. At this time, the tip of the underwater transport pipe 6 is about 1.5 m into the uncured portion 2, as in general underwater concrete pouring.

As mentioned above, the composition of the filling soil is not specific to one type, but in this example, the sand content is 35%, the silt and clay content is 65%, and the water content is 260%. A mixture of 240 kg of water slag as a hardening agent, 36 kg of slaked lime, and 12 kg of sodium silicate as an additive was mixed and stirred for 1.2 m ³ of packed earth and sand. This formulation solidified in one day, and the unconfined compressive strength at that point reached 2.6 kgf/cm ² .

Furthermore, if the packed soil is not transported from land, it can be sucked up from the surrounding seabed using a slurry pump.
The water content is adjusted using a sieve or the like and sent to the mixing plant 10, and the same method as described above is followed.

[Effects of the Invention] Since the present invention is as described above, it is possible to construct a cell at a water depth that is much larger than that possible with conventional construction methods. This effect becomes greater as the radius of the cell becomes larger. Furthermore, as the earth and sand filling the cell solidifies upon completion of construction, a highly safe cell with high shear resistance can be constructed. In this way, the present invention
It is possible to provide a method for constructing a deep water cell that greatly contributes to the construction of a deep water cell and its rapid construction.

Furthermore, it is possible to provide an economical and resource-saving method for constructing a deep water cell by using seabed sediment around the cell.

[Brief explanation of drawings]

Fig. 1 is a sectional view for explaining the charging of filling earth and sand, and Fig. 2 is an overall perspective view of a work barge for carrying out the method of the present invention. 2 - uncured part, 3 - hardened part, 4 - foundation mound, 5 - seabed, 6 - underwater transport pipe, 7 - steel sheet pile cell, 8 - work barge, 9 - hardened material silo, 10 - mixing plant, 11 - Slurry pump and water content ratio adjustment device, 12 - Portal crane, 13 - Residence and control room.

Claims (1)

[Scope of Claims] 1. A cell is installed at a construction site, and filling soil mixed with hardening material and additives is introduced into the cell from the bottom of the cell using an underwater transport pipe, and the above-mentioned filling material is By adjusting the curing start time of the earth and sand in accordance with the feeding speed, the tensile stress generated in the cell shell due to the lateral pressure of the filling earth and sand in the upper unhardened area does not exceed the allowable stress level throughout the cell shell. A construction method for deep water cells characterized by the following. 2 The filling earth and sand described in claim 1 is collected from the seabed around the cell construction site, and the water content ratio is adjusted using a work boat at sea. A method for constructing a deep water cell according to item 1.