JP4058551B2 - Seismic reinforcement method for existing structures - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a seismic strengthening method for existing structures, and more particularly to a seismic strengthening method for existing structures performed on already constructed harbor structures such as caisson quay.
[0002]
[Prior art]
The caisson quay and other bay structures generally receive large horizontal external forces such as earth pressure and water pressure as the water depth increases, so the weight required for the wall also increases rapidly. In many cases, for example, as shown in FIG. 3, a concrete box (hereinafter referred to as a “caisson”) 20 called a concrete caisson 20 is installed on the seabed, and then the caisson 20 is filled with sand 21 and It is constructed by a caisson method which is completed with a concrete lid 22 on top.
[0003]
In addition, when the seabed is relatively soft, a trapezoidal foundation rubble layer 23 is formed by laying a large amount of foundation rubble (such as crushed stone and crushed stone) and built on it. Furthermore, if necessary, the ground improvement is performed by replacing the lower ground 24 of the foundation rubble layer 23 with high-quality soil (replacement sand).
[0004]
By the way, most of the damage caused by the earthquake of this type of port structure is due to the so-called liquefaction of the ground.
[0005]
The Great Hanshin Earthquake has just suffered great damage, and early development of seismic reinforcement methods for harbor structures such as the caisson quay that has already been built is desired.
Up to now, various methods have been developed as seismic reinforcement methods for existing structures such as harbor structures. For example, a liquefaction prevention method that reduces the pore water pressure by driving a perforated sheet pile into the surrounding ground layer (replacement sand) of an existing structure to release excess pore water, or a perforated hollow that penetrates the structure A method of driving piles to the support ground to prevent slipping and liquefaction during an earthquake, as well as drilling through the structure and liquefying the sand directly below or the replacement sand part penetrating the foundation rubble layer The construction method etc. which prevent are known.
[0006]
[Problems to be solved by the invention]
However, any of the above methods may adversely affect the surrounding ground during construction.For example, the foundation rubble that forms the foundation rubble layer due to loose ground during construction or variations in the improved structure There is a problem that there is a possibility of inviting.
[0007]
The present invention was made to solve the above-described problems, and in particular, an earthquake-proof reinforcement method for an existing structure that enables stable ground improvement to a bay structure such as a caisson quay already constructed. The purpose is to provide.
[0008]
[Means for Solving the Problems]
The seismic reinforcement method for an existing structure according to claim 1 is a seismic reinforcement method for an existing structure constructed on a foundation rubble layer constructed by laying a large amount of foundation rubble on the seabed ground, A step of drilling from the upper part of the existing structure to the lower end of the foundation rubble layer with a drilling bit while holding the wall in the casing, and pulling out the drilling bit from the tip of the casing into the foundation rubble layer A basic rubble solidified layer is formed by a process of gradually raising the casing while injecting a solidified material, and then the basic rubble solidified layer is used as an upper lock cover, while holding the hole wall with the casing by a drill bit. Drilling from the upper part of the existing structure to the seabed ground below the foundation rubble solidification layer, and pulling out the casing and the drilling bit to solidify the foundation rubble A step of installing a jetting / stirring rod in the lower seabed ground, and jetting the solidifying material from the tip of the rod into the seabed ground below the foundation rubble solidified layer from the tip of the rod The solidified improved body is formed in the seabed ground below the foundation rubble solidified layer by a step of gradually lifting.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
1 (a) and 1 (b) show an example of a caisson-type gulf structure and its seismic reinforcement method. In the figure, a large number of rubble and crushed stones are laid on the seabed to form a trapezoidal crushed stone layer 1 The caisson quay 2 is constructed on the foundation rubble layer 1 as a caisson-type gulf structure.
[0011]
The caisson quay 2, after sinking a concrete box (hereinafter referred to as “caisson”) 3 made on the ground onto the foundation rubble layer 1, the caisson 3 is filled with a large amount of sand 4 and the caisson 3 It is constructed with a concrete lid 5 on top.
[0012]
Moreover, the submarine ground 6 below the foundation rubble layer 1 is replaced with high-quality soil (sand) over a certain range, and the ground is improved. In addition, a large amount of backfilling spar 7 is filled behind the caisson 3, and a backfilling soil 8 is filled behind the backfilling stone 7.
[0013]
Next, the seismic reinforcement method for the caisson-type gulf structure thus constructed will be described in order (see FIGS. 2A to 2F).
(1) First, a hole is drilled from the upper part or the inside of the caisson-type gulf structure 2 (for example, the ground or the inside of the caisson 3) to the lower end of the foundation rubble layer 1. Drilling is performed by the drill bit 10 without holding the hole wall with the casing 9. Moreover, you may use a super-high-speed jet together in order to improve drilling efficiency as needed.
(2) Next, the drill bit 10 is pulled out, and then the solidified material is discharged from the tip of the casing 9 into the basic rubble layer 1 while gradually lifting the casing 9.
[0014]
At that time, for example, underwater non-separable concrete is used as the solidifying material, and the amount of the solidifying material is appropriately determined according to the porosity and the filling range of the basic rubble layer 1. By solidifying the solidified material discharged into the foundation rubble layer 1, the foundation rubble layer 1 is integrated like a rock mass to form a hard rock cover (base rubble solidification layer).
Next, while holding the hole wall in the casing 9 again, the casing is dug up to the lower end of the improved soil (the lower surface of the layer to be liquefied) formed in the seabed ground below the foundation rubble layer 1 by the drill bit 10. .
Next, the drill bit 10 and the casing 9 are pulled out, and then the injection / stirring rod 11 is installed.
Next, by gradually lifting the injection / stirring rod 11 while injecting the solidified material into the improved soil from the tip, the improved soil and the solidified material are stirred and mixed up to the lower end of the foundation rubble layer 1. The solidified improvement body 12 to be formed is created.
[0015]
At that time, the solidified material is directly integrated into the ground by ultra-high speed jet to reliably integrate the adjacent solidified improvement bodies 12 by the blast effect, and to achieve close contact between the preceding solidification improved body and the subsequent solidification improved body. To do.
[0016]
The above operations are repeated within a predetermined plane range to create a plurality of solidified bodies 12 in the seabed ground below the foundation rubble layer 1 . At that time, since the foundation rubble layer 1 is integrated like a rock and forms a hard rock cover (foundation rubble solidified layer), the fall of the foundation rubble that forms the foundation rubble layer 1 due to loosening during ground improvement In addition, it is possible to reliably prevent variations and the like of the solidified improvement body 12 and to perform extremely reliable ground improvement.
[0017]
In addition, as a method of improving the ground of the seabed below the foundation rubble layer 1 , it is not always necessary to use the method as described above. In short , the seabed ground below the foundation rubble layer 1 is improved to a hard and stable ground. Any known method may be used as long as it can be performed.
[0018]
【The invention's effect】
The present invention has the above-described configuration. In particular, by solidifying the foundation rubble layer, it is possible to reliably prevent the foundation rubble from dropping due to loosening during ground improvement and the variation of the solidified improvement body. It can be carried out.
[0019]
Moreover, since the solidified body of the foundation rubble layer acts as an upper cover (lock cover) during the ground improvement construction, the solidified improved body can be reliably formed.
Furthermore, there is no gap in the basic rubble layer, and it is possible to prevent the outflow of slime and the pollution of seawater.
[Brief description of the drawings]
FIGS. 1A and 1B are cross-sectional views showing 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 support ground of a caisson quay.
FIG. 3 is a cross-sectional view showing an example of a caisson quay.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Foundation rubble layer 2 Caisson quay 3 Caisson 4 Sand 5 Concrete lid 6 Ground 7 Backfill quarry stone 8 Backfill soil 9 Casing 10 Drilling bit 11 Injection / stirring rod 12 Solidification improvement body

Claims (1)

A seismic reinforcement method for an existing structure built on a foundation rubble layer created by laying a large number of foundation rubble on the seabed ground, wherein the existing structure is formed by a drill bit while holding the hole wall with a casing. Drilling from the top of the object to the lower end of the foundation rubble layer, and pulling out the drill bit and gradually pulling up the casing while injecting solidified material into the foundation rubble layer from the tip of the casing Form the foundation rubble solidified layer, then use the foundation rubble solidified layer as the upper lock cover, hold the hole wall with the casing and drill the drill bit from the upper part of the existing structure below the foundation rubble solidified layer a step of boring to seabed in the casing and pull the drilling bit, said injection the basal riprap solidified layer during seabed below and stirring rod Tatekomu process and, seabed below said base riprap solidified layer by a process to increase slowly solidified material is jetting the injection and stirring rod below the seabed in the ground from said base riprap solidified layer from the tip of the rod A seismic reinforcement method for existing structures, characterized in that a solidified improvement body is created in the ground .

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