JPH0615764B2 - Underwater structure scouring prevention method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a scour prevention method suitable for an underwater structure that is submerged in a deep seabed under a strong tide.

<< Prior Art >> The scouring phenomenon for underwater structures such as caisson is widespread and remarkable, especially under strong tide. As a construction method for preventing this type of scour, either a method of improving the ground by reducing the scour force or a method of increasing the scour resistance of the ground is adopted.

However, it is extremely difficult to increase the scour resistance at a deep water and under strong tide. Therefore, although the method for reducing the scour force is adopted, there are problems described below.

<< Problems to be solved by the invention >> That is, the scouring prevention method for reducing the scouring force has conventionally laid a protective material having a surface larger than the horizontal cross section of the underwater structure on the bottom of the water. Since the work is carried out exclusively by underwater work such as a diver, there is a problem that the work efficiency is low and the construction period is prolonged.

The present invention has been made in view of the above-mentioned drawbacks, and an object thereof is to make it possible to carry out the construction of scour prevention work accurately in an extremely short period of time and without underwater work. Means for Means >> To achieve the above object, a method for preventing scour of an underwater structure according to the present invention includes a scaffold arranged around the underwater structure and a plurality of hanging wires extending downward from the scaffold. When,
A scour prevention mat that is supported substantially horizontally by the plurality of hanging wires in an unfolded state is provided, and the scour preventive mat is adjusted in water while maintaining the unfolded state by adjusting the payout amount of each wire. It is characterized by being settled on the water bottom around the structure.

<Operation> According to the scour prevention method for underwater structures of the present invention, the sinking laying work of the scour prevention mat to a predetermined position is performed by the work from the scaffold and the scaffold is provided on the scaffold. By adjusting the feeding amount of each hanging wire, the scour prevention mat is settled in water in a well-balanced manner while maintaining the expanded state of covering the laying position.

<Example> Hereinafter, an example of the method of the present invention will be described in detail with reference to the drawings.

1 to 3 show a first embodiment of the construction method of the present invention, and FIG. 1 is a plan view showing the coupling relationship between a caisson and a scour prevention mat to which the construction method is applied, FIG. 2, FIG. FIG. 4 is a process explanatory view showing a procedure for laying a scour prevention mat in the same construction method.

In each figure, 1 is a cylindrical steel caisson, 2 is a scorching prevention mat for covering the bottom (hereinafter referred to as the first mat) which is laid on the seabed in a state in which the caisson 1 is divided into a plurality of outer peripheral portions ), 3 and 4 are scouring prevention mats for slope covering which are arranged in a double concentric pattern on the outer peripheral surface of the first scouring prevention mat 2 (hereinafter referred to as second and third scouring prevention mats). .

The first scour prevention mat 2 covers the fixed work scaffold 5 assembled on the peripheral portion of the top surface of the caisson 1 through a plurality of suspension wires 6 and covers the laying position and keeps it in an expanded state and in a suspended state. Has been done. Further, the second and third scour prevention mats 3 and 4 are held in a floating state, that is, in a deployed state that covers the laying position on the lower surface of the pontoon 8 through a plurality of suspension wires 6 as well and in a suspended state. There is.

The scour prevention mats 2, 3 and 4 are composed of a chain mat, a concrete mat, a gravel (rubbish) mat, an asphalt mat, a concrete mat, a concrete block mat, etc. It is held at the bottom of 7.

After the construction of the caisson 1 in the construction dock is completed, the first scour prevention mat 2 is assembled with the work scaffold 5 in the outfitting process, and then suspended under the suspending wire 6 under the work scaffold 5. It is held, and in this state, it is towed to the site where Caisson 1 is settled by a tugboat.

Further, the second and third scour prevention mats 3 and 4 are assembled at a place different from the outfitting site, and are towed by the barge 8 underwater, and the barge 8 is towed by a tugboat. Each of them is arranged on the outer peripheral portion of the first scour-prevention mat 2 at the digging site. A plurality of winches 9 corresponding to the suspension wires 6 are provided on the work scaffold 5 and the berth 8.
Is provided.

Therefore, as shown in FIG. 2 at the sunk site, after the caisson 1 is sunk, the pontoons 8 are connected to the outer periphery of the work scaffolds, respectively, and the pontoons 8 are wound after the pontoons 8 are fixed by mooring lines. When returned, each scour prevention mat 2 descends as shown by the imaginary line, and as shown in FIG. 3, the first scour prevention mat 2 is laid on the sea bottom E on the outer peripheral portion of the caisson 1.

In addition, when the second and third scour prevention mats 3 and 4 land on an uneven surface such as slope E ₁ instead of a flat surface,
Since the wires 6 are tensioned or loosened along the shape, the unwinding operation of the winch 9 can be performed while observing the tension, so that the wire can be laid in a state corresponding to the uneven shape.

Since this work is performed under strong tide, by operating the winch 9 according to the tension state of each wire 6, it can be laid accurately at the intended installation position.

In addition, during laying work, each scour prevention mat 2, 3,
By connecting the four mats or the adjacent mats with a wire or the like, the gap between the mats is small and a large scour prevention effect can be obtained.

The scour prevention mats 2, 3, 4 and the suspension frame 7 can be separated from each other by an appropriate remote operation.

Next, FIG. 4 shows a second embodiment of the method of the present invention.

In the figure, the first scour prevention mat 2 is fixed to the lower part of the work scaffold 5 in the same manner as described above, in a deployed state that covers the laying position at the lower part of the suspension frame 7, and in the suspended state, The suspension frame 7 is held under the scaffold 5 by a guide wire 6 '.

And this 1st scour prevention mat 2 is connected to the crane 20 via the wire 6 for suspension instead of the said winch 9, and it descends | decreases and it lays down on the seabed E like the above. It

Unlike the first embodiment, the scour prevention mat 10 on the outer peripheral side is supported by the lower portion of the suspension frame 7 in an integrated state.

And this is the crane 31 provided on the crane ship 30.
In addition, it is carried to the submerged site in a suspended state through a plurality of suspension wires 6, and is laid by the operation of the crane 31 while being joined to the outer periphery of the first scour prevention mat 2. .

According to the present embodiment, the scour prevention mats cannot be simultaneously sunk as compared with the first embodiment, and the crane 20 and the crane ship 30 are sequentially operated, so that the sea bottom on the outer periphery of the caisson 1 is Will be laid in sequence,
Since the work is performed by one crane 20 and one crane ship 30, the construction period is extended, but the equipment cost is lower than that of the first embodiment.

<< Effects of the Invention >> As described in detail above, according to the scour prevention method for an underwater structure of the present invention, the scour prevention mat can be easily and quickly laid by working from the sea surface. At the same time, the amount of each hanging wire is adjusted to settle while maintaining the developed state of the scour prevention mat, so that the scour can be performed accurately at the specified laying position and following the unsealed part of the sea floor. The prevention mat can be laid down by sedimentation.

[Brief description of drawings]

1 to 3 show a first embodiment of the present invention, FIG. 1 is a plan view showing the positional relationship between a caisson and a scour prevention mat, and FIGS. 2 and 3 are scour in the same construction method. FIG. 4 is an explanatory sectional view showing a scour procedure for the prevention mat, and FIG. 4 is an explanatory diagram showing a second embodiment of the method of the present invention. 1 ... Caisson (underwater structure) 2, 3, 4, 10 ... Scour prevention mat 5 ... Work scaffolding, 6 ... Suspension wire 8 ... Barge (floating body) 9 ... Winch, 20, 31 ... …crane

Claims (5)

[Claims] 1. A scaffold disposed around an underwater structure, and a plurality of suspension wires extending downward from the scaffold, respectively.
A scour prevention mat that is supported substantially horizontally by the plurality of hanging wires in an unfolded state is provided, and the scour preventive mat is adjusted in water while maintaining the unfolded state by adjusting the payout amount of each wire. A scour prevention method for underwater structures, characterized by being settled on the water bottom around the structure. 2. The scour prevention method for an underwater structure according to claim 1, wherein the scaffold is a fixed scaffold that is provided around the underwater structure in an extended state. 3. The scaffold is composed of a fixed scaffold provided in an extended state around an underwater structure, and a floating body which is in an outer peripheral portion of the fixed scaffold and holds the scour prevention mat in a suspended state in water. The method for preventing scouring of an underwater structure according to claim 1, wherein 4. The washing of an underwater structure according to any one of claims 1 to 3, wherein a winch for paying out the hanging wire is used as the means for sinking. Excavation prevention method. 5. A scour prevention method for an underwater structure according to any one of claims 1 to 3, wherein a crane is used as the means for sinking.