JP2750449B2 - Open caisson laying method and equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an open caisson laying method and an apparatus therefor.

<Conventional Technology> In general, when an open caisson is likely to be subsided when it is submerged on the seabed, the Tsukishima method is often used.

However, when it is not possible to build an island due to construction conditions, a fixed type oversinking lid that temporarily blocks the caisson's skeleton may be temporarily laid.

However, when the oversink prevention lid is a fixed type, it is difficult to adjust the balance between the reaction force due to the internal pressure generated in the oversink prevention lid and the settlement load.

Therefore, there is a method of gradually lowering the frame using a reaction plate having a movable anti-sinking lid.

The reaction plate in this method consists of the reaction plate main body and a sealing material attached to the periphery of the reaction plate.The tension member is fixed to the skeleton, and the reaction plate is fixed to the inside of the body by the center hole jack installed on the upper surface of the reaction plate. Move up and down along to balance the self-weight and reaction force.

<Problems to be solved by the present invention> The following problems exist in the above-mentioned conventional laying technique.

<B> The seal around the reaction force plate is not very reliable, and the pressure inside the reaction force plate is considerably large, so that compressed air leaks from the seal and the balance between its own weight and the reaction force becomes insufficient. Prone to subsidence.

<B> At the time of submersion on the sea floor, seawater may squirt together with compressed air from the peripheral seal, causing the jack installed on the upper surface of the reaction plate to submerge, making the caisson impossible to submerge. There is.

<Object of the present invention> The present invention has been made in order to solve the above-described problems, and it is an object of the present invention to provide an open caisson laying method and a device capable of reliably preventing the caisson from sinking excessively. Aim.

<Configuration of the Present Invention> Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

In this embodiment, an open caisson frame 1 having a circular cross section will be described as an example.

<B> Reaction plate (FIGS. 1 to 3) The reaction plate 2 is a plate disposed in the open caisson frame 1 in the horizontal direction.

The shape of the reaction force plate 2 is, for example, a disk shape having an outer diameter slightly smaller than the inner diameter of the caisson frame 1, as shown in FIG.

An opening 21 is opened at the center of the reaction force plate 2, and a pipe 22 for securing a working space or the like is set up from the periphery of the opening 21 to the vicinity of the top end of the caisson frame 1. .

<B> PC steel wire for lifting (FIGS. 1 to 3) The PC steel wire for lifting 3 is arranged in the caisson frame 1 in the vertical direction.

The lower end of the pull-up PC steel wire 3 penetrates the peripheral edge of the reaction force plate 2 and is fixed by a fixing portion 31 on the lower surface of the reaction force plate 2.

On the other hand, a bracket 32 is attached near the top end of the inner peripheral surface of the caisson frame 1, and a center hole jack 33 is installed on the upper surface of the bracket 32.

The upper portion of the lifting PC steel wire 3 is gripped by the center hole jack 33.

The number of PC steel wires 3 for lifting and the number of the center hole jacks 33 to be attached are appropriately selected depending on the weight of the reaction force plate 2 so that the reaction force plate 2 can be moved up and down.

<C> PC steel wire for lowering (Figs. 1 to 3) The PC steel wire for lowering 4 is buried in the caisson frame 1 in a longitudinal direction by covering it with a sheath 41, and the lower end is a U-shaped sheath 42.
The upper part of the caisson frame 1 is exposed to the hollow part of the caisson body 1, and the upper end of the exposed part penetrates the periphery of the reaction force plate 2, and is fixed by the fixing part 43 on the upper surface of the reaction force plate 2.

Note that a reinforcing material 44 such as H steel is embedded inside the U-shaped sheath 42.

On the other hand, a center hole jack 45 is installed at the top end of the caisson body 1, and the upper part of the PC steel wire 4 for pulling down is gripped by the center hole jack 45.

The required number of PC steel wires 4 for lowering and the number of center hole jacks 45 to be attached are set so as to sufficiently withstand the reaction force when the caisson skeleton 1 is laid down.

<D> Cutting device (Fig. 4) A space pocket 5 is secured in advance around the lowering PC steel wire 4 in the caisson frame 1, and a thermite agent 51 and a charging bridge 52 are set therein. deep.

The embedding position of the thermite agent 51, that is, the scheduled cutting position is around the lower end of the PC steel wire 4 for lowering in an arbitrary range where the tension is applied, and to what extent the tension is applied to the PC steel wire 4 for lowering. Whether or not to add is determined in consideration of construction conditions and the like.

Further, an injection hole 53 for injecting a fixing agent is provided around the lowering PC steel wire immediately above the burying position of the thermite agent 51, that is, around the lower end of the portion to be cut.

<Operation of the Present Invention> Next, the operation of the present invention will be described.

<B> Ensuring the reaction force at the time of subsidence Activate the center hole jack 33 and lift the PC
The reaction plate 2 in the caisson frame 1 is positioned on the soft ground 6 via the steel wire 3.

Next, the center hole jack 45 is operated to pull the upper part of the PC steel wire 4 for pulling upward, and to press the lower surface of the reaction force plate 2 against the surface of the soft ground 6 to take a reaction force from the ground. .

Then, the reaction force taken from the ground can be transmitted to the caisson skeleton 1 via the reaction force plate 2 and the PC steel wire 4 for lowering.

As the caisson frame 1 sinks, the clamshell bucket 7 or the like discharges the sediment pushed up from the opening 21 of the reaction plate 2 and sinks it to a predetermined depth of the foundation ground layer 8.

<B> Introduction of pre-stress After the caisson skeleton 1 is sunk to a predetermined depth, the arrival bridge 52 causes the thermite 51 to generate heat and lowers it.
Cut the middle of PC steel wire 4.

Next, a fixing agent such as grout is injected from the injection hole 53,
The cut lower end of the pull-down PC steel wire 4 is fixed in the caisson frame 1.

Then, the upper portion of the pull-down PC steel wire 4 is pulled upward by the center hole jack 45 to be tensioned, so that a predetermined prestress can be introduced into the caisson frame 1.

<Effects of the Present Invention> Since the present invention has been described above, the following effects can be expected.

<A> The conventional method using a movable reaction force plate has poor reliability of the peripheral seal, and the pressure inside the reaction force plate is considerably large. And the balance between them is insufficient, and oversubsidence is likely to occur.

On the other hand, according to the present invention, the reaction force for sinking the caisson can be obtained directly from the ground by pressing the lower surface of the reaction plate against the ground.

Therefore, the weight of the caisson can be supported by the excavated ground having a large area.

Therefore, a stable reaction force can be obtained, and oversinking can be reliably prevented.

<B> With the conventional method using a movable reaction force plate, when sinking to the sea floor, seawater squirts together with compressed air from the peripheral seal part, and the jack installed on the upper surface of the reaction force plate submerges Problems may occur and caisson laying may not be possible.

In contrast, in the present invention, the center hole jack is attached to the top end of the caisson.

Therefore, the jack is not submerged, and the caisson laying operation can be favorably performed.

<C> Conventionally, compressed air intervenes between the bottom surface of the over-subsidence prevention cover and the excavation surface at the lower end of the caisson (seawater has also penetrated in the case of submarine ground subsidence). The caisson's own weight and the reaction force are balanced by adjusting the pressure of the compressed air.

Therefore, it is necessary to provide a seal on the periphery of the over-subsidence prevention lid to prevent leakage of compressed air (and ejection of seawater).

However, in the case of the present invention, compressed pressure is not interposed between the pressure plate and the excavated ground surface because the pressure plate is pressed against the excavated ground surface to directly take a reaction force.

 Therefore, there is no need to provide a seal around the pressure plate.

Further, depending on the degree of softness of the excavated ground for taking the reaction force, the reaction plate may have a simple cross-girder structure.

Therefore, the structure of the entire apparatus is simple and economical.

<D> When a large horizontal load is applied to the caisson after laying, prestress can be introduced into the caisson frame using the PC steel wire used at the time of laying.

Therefore, it is possible to construct a structure that can sufficiently withstand a large horizontal load.

[Brief description of the drawings]

 Fig. 1: Illustration of one embodiment of the present invention Fig. 2: Horizontal sectional view of caisson Fig. 3: Enlarged explanatory drawing of main part Fig. 4: Explanatory drawing of prestressing method

Claims (5)

(57) [Claims] 1. A vertically movable reaction force plate disposed horizontally in an open caisson; a lifting PC steel wire having a lower end fixed to the reaction force plate and disposed vertically in the caisson; A center hole jack installed near the top end of the caisson and a vertical hole inside the caisson skeleton.The lower end is exposed inside the caisson and folded upward. Opening characterized by a lowering PC steel wire whose upper end is fixed to a reaction force plate, and a center hole jack that holds the upper part of the lowering PC steel wire and is installed near the top end of the caisson. Caisson sinking equipment. 2. An open caisson laying device according to claim 1, wherein the reaction plate has an opening in a central portion thereof and extends from a peripheral portion of the opening to a vicinity of a caisson top end. An open caisson sinking device constructed by starting up a tube. 3. A submerging method using an open caisson submerging device according to claim 1 or 2, wherein a reaction plate in the caisson is positioned on the ground, and An open caisson squatting method in which the upper part is pulled upward by a center hole jack, and the caisson is sunk while reacting to the ground by pressing the lower surface of the reaction force plate against the ground. 4. The lowering apparatus for an open caisson according to claim 1 or 2, wherein the lowering PC steel wire is melted and cut around a part of the lowering PC steel wire in the caisson body. An open caisson laying device, wherein a melting agent is buried, and an injection hole for injecting a fixing agent is provided around a lowering PC steel wire immediately above the melt burying position. 5. A submerging method using an open caisson submerging device according to claim 4, wherein the caisson is submerged to a predetermined depth, and then the melting PC is used to cut a part of the PC steel wire for pulling down. Next, a fixing agent is injected from the injection hole, and the cut lower end of the lowering PC steel wire is fixed in the caisson body, and the upper portion of the lowering PC steel wire is pulled upward by a center hole jack to be tensioned. An open caisson sinking method that introduces prestress into the frame.