JP2000248527A - Seismic retrofitting of existing structures - Google Patents

Abstract

(57) [Summary] [PROBLEMS] To provide a seismic retrofitting method for an existing structure capable of performing stable ground improvement for a Gulf structure such as a caisson quay already constructed. SOLUTION: A large amount of foundation rubble is spread under a caisson quay 2 and a solidifying material is discharged to a foundation rubble layer 1 formed to form a foundation rubble solidification layer. Perform ground improvement on the ground. At that time, the rod 11 for injection and agitation was erected on the lower ground of the solidified rubble layer,
By gradually pulling up the injection / stirring rod 11 while injecting the solidified material from the tip thereof, the ground improvement is performed on the ground below the solidified solid foundation layer.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a seismic retrofitting method for an existing structure, and more particularly to a seismic retrofitting method for an existing structure which is carried out on a harbor structure such as a caisson quay.

[0002]

2. Description of the Related Art Gulf structures such as caisson quays generally receive large horizontal external forces such as earth pressure and water pressure as the water depth increases. Many deep port structures are
For example, as shown in FIG. 3, after a concrete box (hereinafter referred to as a “caisson”) 20 called a concrete caisson is installed on the seabed, sand 21 is filled in the caisson 20 and concrete is placed on the sand 21. It is constructed by the caisson method of completing with a lid 22 made of steel.

If the seabed is relatively soft, a large amount of basic rubble (such as crushed stone or crushed stone) is laid to form a trapezoidal basic rubble layer 23, which is constructed thereon. Furthermore, if necessary, the ground below the foundation rubble layer 23 is replaced with good-quality soil (replacement sand) to improve the ground.

By the way, most of the damage of this kind of harbor structure due to the earthquake is caused by so-called liquefaction of the ground, and it is often difficult to recover once a great damage is caused during the earthquake.

[0005] The Great Hanshin Earthquake, which has just been severely damaged, demands early development of a seismic retrofitting method especially for already constructed harbor structures such as caisson quays. Until now, various methods have been developed as seismic reinforcement methods for existing structures such as port structures. For example, a liquefaction prevention method in which a perforated sheet pile is driven into the surrounding ground layer (replacement sand) of an existing structure to reduce excess pore water pressure to reduce pore water pressure, or a perforated hollow through a structure A method of driving a pile into the supporting ground to prevent slippage and liquefaction during an earthquake, and also drilling a structure and liquefying it by improving the ground directly underneath the sand or the replacement sand part that has penetrated the base rubble layer There are known construction methods for preventing such problems.

[0006]

However, any of the above-mentioned construction methods may adversely affect the surrounding ground at the time of construction. For example, the foundation which forms the foundation rubble layer due to loosening of the ground at the time of construction. There are problems such as the possibility of dropping of rubble and variation of the improved compact.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems. In particular, the present invention relates to an existing structure capable of performing a stable ground improvement with respect to a gulf structure such as a caisson quay already constructed. The purpose is to provide a seismic retrofitting method.

[0008]

As a means for solving the above-mentioned problems, a method for seismic reinforcement of an existing structure according to the present invention is characterized in that a large amount of foundation rubble is provided below the existing structure. The solidified material is discharged into the basic rubble layer formed by laying to form a basic rubble solidified layer, and then the ground below the ground rubble solidified layer is improved.

According to a second aspect of the present invention, in the seismic retrofitting method for an existing structure according to the first aspect, a jetting / stirring rod is erected on the ground under the rubble solidified layer, and the jetting / stirring rod is attached to the ground from its tip. The ground is gradually improved by injecting the solidified material into the ground and gradually raising it, thereby improving the ground below the ground solidified layer.

[0010]

1 (a) and 1 (b) show an example of a caisson-type bay shore structure and its seismic retrofitting method. In the figure, a large amount of rubbish such as crushed stone or crushed stone is spread on the sea floor. A trapezoidal basic rubble layer 1 is formed, and a caisson quay 2 is constructed on the basic rubble layer 1 as a caisson-type bay shore structure.

The caisson quay 2 is prepared by submerging a concrete box (hereinafter referred to as “caisson”) 3 made on the ground on the foundation rubble layer 1 and then filling the caisson 3 with a large amount of sand 4. And a concrete lid 5 on the caisson 3
Is built.

Further, the lower ground 6 of the foundation rubble layer 1 is replaced with good-quality soil (sand) over a certain range to improve the ground. The back of the caisson 3 is filled with backfilling stones 7 in large quantities, and the back of the backfilling stones 7 is filled with backfilling soil 8.

Next, the seismic retrofitting method for the caisson-type bay shore structure thus constructed will be described in order (FIG. 2).
(See (a) to (f)). First, a hole is drilled from the upper part or the inside (for example, the ground or the inside of the caisson 3) of the caisson-type shore structure 2 to the lower end of the foundation rubble layer 1. For drilling, the hole wall is covered with casing 9.
The drilling is performed by the drill bit 10 while keeping the pressure. If necessary, an ultra-high-speed jet may be used in order to increase the drilling efficiency. Next, the drill bit 10 is pulled out, and then the casing 9 is removed.
The solidified material is discharged from the front end of the casing 9 into the basic rubble layer 1 while gradually lifting up.

At this time, for example, underwater inseparable concrete is used as the solidifying material, and the amount of the solidifying material is appropriately determined according to the porosity and filling range of the basic rubble layer 1. Basic rubble layer 1
When the solidified material discharged into the inside is solidified, the basic rubble layer 1
Are integrated like a bedrock to form a hard rock cover (basic rubble solidified layer). Next, while the hole wall is held in the casing 9 again, the casing is dug up to the lower end (the lower surface of the liquefaction target layer) of the improved soil formed below the foundation rubble layer 1 by the drill bit 10. Next, the drill bit 10 and the casing 9 are pulled out,
Thereafter, the injection / stirring rod 11 is installed. Next, the injection / stirring rod 11 is gradually pulled up while injecting the solidified material into the improved soil from its tip, so that the improved soil and the solidified material are stirred and mixed to the lower end of the basic rubble layer 1. The solidified body 12 to be formed is formed.

At this time, the solidified material is directly jetted into the ground at an ultra-high speed so that the adjacent solidified improved bodies 12 are surely integrated by the blast effect, and the close contact between the preceding solidified improved body and the following solidified improved body is improved. Shall be considered.

The above operation is repeatedly performed within a predetermined plane range to form a plurality of solidified improved bodies 12 under the basic rubble layer 1. At this time, since the basic rubble layer 1 is integrated like a bedrock to form a hard rock cover (basic rubble solidified layer), the drop of the basic rubble layer 1 forming the basic rubble layer 1 due to loosening during ground improvement. And the variation of the solidification improvement body 12 can be reliably prevented, and extremely reliable ground improvement can be performed.

The method for improving the ground below the foundation rubble layer 1 does not necessarily have to be the above-mentioned method. In short, the ground below the foundation rubble layer 1 is converted into a hard and stable ground. A known method may be used as long as the method can be improved.

[0018]

The present invention has the above-described construction, and particularly by solidifying the foundation rubble layer, it is possible to reliably prevent the fall of the foundation rubble due to the loosening at the time of ground improvement and the dispersion of the solidified improved body. Stable ground improvement can be performed.

In addition, since the solidified rubble layer works as an upper cover (lock cover) during ground improvement work,
The formation of the improved solidified body can be reliably performed. further,
There is no void in the basic rubble layer, and slime outflow and seawater pollution can be prevented.

[Brief description of the drawings]

FIGS. 1A and 1B are cross-sectional views illustrating a caisson quay and its seismic reinforcement method.

FIGS. 2A to 2F are construction diagrams showing an example of a ground improvement method performed for the purpose of seismic reinforcement in a supporting ground of a caisson quay.

FIG. 3 is a sectional view showing an example of a caisson quay.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 foundation rubble layer 2 caisson quay 3 caisson 4 sand 5 concrete lid 6 ground 7 backfill split stone 8 backfill soil 9 casing 10 drill bit 11 injection / stirring rod 12 solidified improved body

Claims (2)

[Claims] Claims: 1. In a seismic retrofitting method for an existing structure constructed on a foundation rubble layer formed by laying a large amount of foundation rubble stone, a solidifying material is discharged into the foundation rubble layer to form the foundation rubble solidification layer. Forming, and then performing ground improvement on the ground below the solidified rubble solidification layer, a seismic retrofitting method for existing structures. 2. An injection / stirring rod is erected on the lower ground of the base rubble solidification layer, and the injection / stirring rod is gradually pulled up while injecting the solidification material from the tip thereof, so that the basic rubble solidification layer is formed. 2. The method of claim 1, wherein the ground is improved on the lower ground.