JPS637411A - Seismic reinforcement method for existing port structures - Google Patents

Abstract

PURPOSE:To prevent the liquefaction of sand in the neighborhood of a double steel shell by a method in which the double steel shell consisting of an outer shell with many small holes and an inner shell to be inserted into the outer shell with a given spacing is set near an existing caisson structure. CONSTITUTION:A double steel shell 10, consisting of an outer shell 11 with many small holes and an inner shell 12 inserted with a given spacing into the shell 11, is set in the ground near an existing caisson structure 40 by setting its lower end to the bearing ground 1 and also by positioning the intermediate part of the shell 11 in sandy ground 2. The upper end of the shell 10 is projected into sea, broken stones and soil are packed into the shell 12, and the upper part of the shell 12 is covered with concrete 14. The soil between both of the shells 12 and 11 is removed. The liquefaction of sand in the range L' near the shell 10 can thus be prevented, generating slide resistance against the land slide face.

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to a construction method for seismically reinforcing an existing port structure located on gravel ground that is likely to liquefy during an earthquake.

(b) Conventional technology It is generally known that when an external earthquake force is applied to sandy ground containing a large amount of moisture, a liquefaction phenomenon occurs in which the sandy ground behaves as if it were a liquid. This phenomenon occurs when water pressure between sand particles rapidly increases due to local shear deformation of the sandy ground, creating a water flow, which causes the sand particles to flow.

Structures constructed on sandy ground that may liquefy during such earthquakes include quay walls and seawalls 1 on beaches and the like. Figure 2 shows typical examples of conventional seismic reinforcement methods for existing port structures located on such ground.

FIG. 2 is a cross-sectional view of an example of a seawall made of a caisson structure, which is one of the port structures. On the support ground g11,
There is sandy ground 2 that may become liquid during an earthquake.

A rubble mound 3 is provided on sandy ground 2, a caisson 4 is placed on top of it, and sand, stones, etc. are packed into it, and backfill earth and sand 5 is piled up on the opposite side of the water surface to form a seawall. Ru.

Hereinafter, for convenience of explanation, the caisson 4 filled with earth and sand, the rubble mound 3, etc. will be referred to as a caisson structure 40.

In seismic reinforcement design, a "slip surface" 6 is set during an earthquake. If the sandy ground 2 has the possibility of liquefaction during an earthquake, resistance to sliding force cannot be expected, but resistance is expected only in the area of the backfill soil 5.
That alone is not enough.

Therefore, in the conventional seismic reinforcement method, in order to reinforce the caisson structure 40, crushed stone,
Improved ground 7 is provided with sand, etc.

The improved ground 7 is expected to release excess pore water pressure in the sandy ground 2 and generate aftereffect ground 8 in the event of an earthquake. If the improvement range is taken as the aftereffect range and the aftereffect range is taken as 2, then an area of L11 can resist the sliding force during an earthquake. Therefore, in the design, the range of L is determined so that the sliding force and the resistance force are equal.

However, the range of L needs to be long depending on the material used, and the range of l also has many unknown points and cannot be specified depending on the substitution method.

In addition, various proposals have been made for liquefaction prevention construction methods, but they have advantages and disadvantages in terms of construction method and economic efficiency, and the effectiveness of many of them has not been quantitatively understood.

(c) Problems to be solved by the invention The problems to be solved by the invention are that it is possible to prevent liquefaction and slippage during earthquakes for the ground that supports existing caisson structures. The objective is to obtain a simple seismic reinforcement method.

(d) Means for Solving the Problems The seismic reinforcement method of the present invention consists of a double shell consisting of an outer shell with a large number of small holes and an inner shell inserted into the outer shell at a predetermined interval. When pouring a plurality of steel plate cells into the ground near an existing port structure, the lower end of the double steel plate cell is embedded into the supporting ground, and the middle part of the cell where the small hole is provided is liquefied during an earthquake. The above-mentioned problems are solved by locating it on sandy ground where there is a possibility of erosion, and by removing the earth and sand that has entered between the outer shell and the inner shell.

(e) Examples Specific examples of the seismic reinforcement method of the present invention will be described with reference to the drawings.

The installation situation of the seawall using the caisson structure 40 shown in FIG. 1 is the same as the installation situation of the seawall shown in FIG. Accordingly, identical reference numbers refer to identical items.

In the construction method of the present invention, first, a double steel plate cell 10 as schematically shown in FIGS. 1 and 3 is prepared. The double steel plate cell 10 is made by bending a thick steel plate and then welding it. The double steel plate cell 10 is made up of an outer shell 11 provided with a large number of small holes, and an inner shell 12 inserted into the outer shell 11 at a predetermined interval. The outer shell 11 and the inner shell 12 are connected and reinforced by ribs 13. Although the shape of the small hole may be arbitrary, a circular shape is preferable from the viewpoint of stress concentration and processing difficulty.

Next, the double steel plate cell 10 is embedded in the ground near the existing caisson structure (in the illustrated embodiment, on the sea side). As shown in FIG. 4, this embedding step is performed using a conventional vibrohammer 20 or, although not shown, a method such as water jet or suction.

The lower end of the double steel plate cell 10 is embedded into the supporting ground 1, and the middle part provided with a small hole is placed in sandy ground that may liquefy during an earthquake. The upper end of the double steel plate cell 10 is made to protrude into the sea.

The inside of the inner shell 12 of the double steel plate cell 10 is filled with crushed stones, earth and sand, and the upper part is covered with concrete 14. Inner shell 1
The earth and sand between 2 and the outer shell 11 are removed to the outside by a conventional suction method.

(to) Effect The operation of the seismic reinforcement method of the present invention will be explained.

As shown in FIG. 1, the excess pore water pressure generated in the sandy ground 2 during an earthquake through the small holes provided in the outer shell 11 of the cell 10 is
It is dissipated by draining water from the top of the cell 10 into the sea. In this way, the sandy ground 2 prevents liquefaction in the area L' near the cell 10.

Furthermore, since the double steel plate cell 10 is embedded into the supporting ground 1, it generates sliding resistance against the sliding surface 6. These two effects are synergized to provide a superior reinforcing effect compared to conventional construction methods.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram of the construction method of the present invention, and FIG. 2 is a schematic explanatory diagram of the conventional construction method. FIG. 3 is a perspective view of a double steel plate cell based on the construction method of the present invention, and FIG. 4 is an explanatory diagram showing an example of a method for embedding the double steel plate cell. 1: Supporting ground 2: Sandy ground 3: Rubble mound 4: Caisson 5: Backfill earth and sand 6: Slip surface 7: Improved ground 8: Remaining ground 10: Double steel plate cell 11: Outer shell 12: Inner shell 13: Rib 14: Concrete 20: Vibrohammer (5 people outside) Figure 2

Claims (1)

[Claims] A plurality of double steel plate cells consisting of an outer shell with many small holes and an inner shell inserted into the outer shell at a predetermined interval are poured into the ground near the existing port structure, and the ground is In the reinforcing construction method, the lower end of the double steel plate cell is embedded into the supporting ground, and the middle part of the cell with a small hole is located in sandy ground that is likely to liquefy during an earthquake; A seismic reinforcement method for existing port structures that is characterized by removing earth and sand that has entered between the outer shell and the inner shell.