JP2976390B2 - Method for preventing liquefaction of the foundation directly under the existing structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a building constructed on the ground where liquefaction may occur during an earthquake,
Alternatively, the present invention relates to a method for suppressing liquefaction of an existing structure, such as a seawall structure, in a direct foundation.

[0002]

2. Description of the Related Art Liquefaction countermeasures are roughly divided into two types: a method for preventing liquefaction from occurring due to ground improvement solidification, and a method for laying various artificial drain materials on a target ground where liquefaction may occur. There is a method that suppresses the rise of excess pore water pressure and suppresses liquefaction by dissipating excess pore water pressure in the target ground through an artificial drain material during an earthquake, but all construction methods are vertically downward from the ground It is based on the construction of.

As the latter artificial drain material for liquefaction countermeasures, a crushed stone drain composed of crushed stone columns formed using a casing in the ground (for example, Japanese Patent Application Laid-Open No.
100919), a resin-made perforated pipe installed in the ground using a casing (for example,
-11990), a perforated steel pipe with a filter (for example, see Japanese Patent Publication No. 4-59405), and the width and thickness of a resin paper drain conventionally used for consolidation of the ground are increased to prevent liquefaction. There is known a plate-shaped drain material (for example, one having a width of 150 mm, a plate thickness of about 10 to 15 mm, and a filter provided around it).

[0004]

The liquefaction countermeasure by ground improvement solidification can be a fundamental countermeasure in the absence of a structure, but on the other hand, it requires a large amount of work, and it is generally difficult to improve an existing structure directly under the ground. It is.

In the liquefaction countermeasure method using various artificial drain materials, when an existing structure exists directly above the ground requiring a liquefaction countermeasure or is used as a work yard or the like, the ground is left as it is. Liquefaction countermeasures cannot be constructed from the surface.

In the case of an artificial drain material made of resin or metal, it is possible to work diagonally downward from the ground around the structure toward the center of the structure. For, a range where no liquefaction countermeasures can be taken remains.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problem, and has a liquid state capable of effectively suppressing liquefaction of a foundation directly under the structure without affecting existing structures on the ground. The purpose is to provide a method for deterring humanization.

[0008]

According to a first aspect of the present invention, there is provided a method for suppressing liquefaction of a foundation directly under an existing structure, comprising constructing a tunnel under the existing structure under the ground and suppressing liquefaction from within the tunnel. The artificial drain material is radially installed in the foundation directly under the existing structure, and the excess pore water pressure at the time of the earthquake is dissipated through the artificial drain material and the tunnel to suppress the liquefaction of the target ground.

The construction method of the tunnel crossing the existing structure is not particularly limited, and various shield methods and other various tunnel methods may be selected according to the construction conditions.

However, since the purpose is to suppress liquefaction, the construction is usually performed on a loose sandy ground with a high groundwater level or in the vicinity thereof, or the space (artificial drainage material can be constructed from inside the tunnel) ( For example, in the case of making a perforation for installing an artificial drain material using a boring machine from inside a tunnel, it is desirable to have a tunnel inner diameter of 2 to 3 m or more.) Deemed desirable.

In general, the tunnel itself is constructed in the ground where liquefaction is to be suppressed. However, depending on the construction of the target ground where the liquefaction is likely to be shallow or other construction conditions, It may be not in the ground but in the vicinity.

As the artificial drain material, various existing artificial drain materials used for suppressing liquefaction as described in the section of the prior art can be used.

[0013] Of these, the resin-made plate-shaped drain material is also suitable for construction from a relatively narrow space in a tunnel because of its flexibility, and by reducing the diameter of the tunnel, the overall diameter is reduced. Construction costs can also be reduced.

Further, in the case of an artificial drain material of a type in which a number of small holes are formed in a resin pipe or steel material and a drainage channel is formed in combination with a filter, it takes time and effort to add these in the construction from inside the tunnel. On the other hand, since the drainage efficiency is good, a sufficient liquefaction suppression effect can be expected even with a small pitch and a large pitch compared to the plate-shaped drain material.

In addition, it is possible to use a resin in which a drainage space is formed by knitting a resin into a pipe shape, a drainage member having a three-dimensional net-like structure made of various fiber materials, and the like.

[0016] Claim 2 restricts the method of installing the artificial drain material in the liquefaction suppressing method according to claim 1,
In this case, a boring machine is used to penetrate the tunnel wall from the inside of the tunnel to the target ground, and an artificial drain material is installed in the hole.

As a boring machine, for example, there is a hydraulic percussion drill conventionally used for anchoring work, drilling a ground injection hole, tunneling work, etc., and drilling a required length while adding a rod. Can be.

When the artificial drain material is made of steel and has strength itself, only the tunnel wall is pierced, and the artificial drain material is pressed into the target ground while extending the artificial drain material through the hole formed in the tunnel wall. You can also go.

In excavation of a tunnel, it is usually necessary to stop water in the perforated portion in order to prevent water leakage from the outer periphery of the perforated portion into the tunnel.

In addition, it is also possible to form a hole with a lid in advance in the segment constituting the lining of the shield tunnel in accordance with the installation pitch of the artificial drain material.

In a third aspect of the present invention, in the method for preventing liquefaction of an existing structure, the water collected in a tunnel through an artificial drain material is drained from a shaft.

Normally, since the tunnel is located below the groundwater level, the inside of the tunnel is always filled with water collected through the artificial drain material.

In the event of an earthquake, excessive pore water pressure increases in the ground subject to liquefaction suppression, but the pressure can be dissipated through artificial drain materials and tunnels, and the rise in excess pore water pressure is suppressed. Thus, liquefaction in the target ground is suppressed.

In this case, the deterrent effect can be enhanced by securing a drainage path from inside the tunnel. Claim 3 describes the water collected in the tunnel,
The outside of the tunnel is drained through a shaft constructed during the construction of the tunnel.

The drainage destination may be on the ground or a separately provided drainage channel. Further, for example, it is possible to forcibly drain the water by using a pump that operates upon detecting an earthquake.

[0026]

1 and 2 show an embodiment in which the present invention is applied to a caisson-type quay straight foundation board which is an existing structure. In the drawing,
The dimensional relationship is different from the actual one.

In FIG. 1, a caisson as an existing structure 1 constituting a quay is installed on a foundation rubble 2 and the caisson is filled with sand 3. A backfill 4 is provided on the back of the caisson.

Under these circumstances, the existing structure 1
Is a loose and loose sandy ground below the groundwater level, and is a liquefaction-preventing ground 5 that may be liquefied.

As a countermeasure, in this example, a shield tunnel starting shaft is constructed in a yard having no obstacles (restrictions) on the ground surface (not shown), and a shield machine is started from the starting shaft, and the existing structure 1 is started. A shield tunnel 6 that crosses below (in this example, inside the liquefaction suppression target ground 5) is constructed.

Subsequently, a hole is made radially in the liquefaction suppression ground 5 using a boring machine or the like from inside the shield tunnel 6, and an artificial drain material 7 such as a plate drain material made of resin is laid. Of course, the artificial drain material is not limited to the plate-shaped drain material, and various existing drain materials can be used. However, the crushed stone drain is difficult to construct except at the bottom and has low water permeability, and therefore is not suitable for the present invention.

In this example, artificial drain members 7 are radially arranged in a direction perpendicular to the tunnel with respect to a point on the central axis of the tunnel of the shield tunnel 6, and at a predetermined interval in the tunnel axial direction as shown in FIG. An artificial drain material 7 is arranged.

The pitch in the tunnel axis direction is 50 to 50 in the case of the ordinary plate-shaped drain described in the section of the prior art.
It is considered that about 100 cm is appropriate, and the same applies to the direction perpendicular to the tunnel. However, the appropriate pitch of the artificial drain material 7 varies depending on the ground conditions and the type of the drain material.

[0033]

According to the present invention, measures for preventing liquefaction of the foundation directly under the existing structure, which have been considered impossible to construct, can be performed without affecting the ground portion.

The water collected by the artificial drain is drained through a shield tunnel to suppress an excessive rise in pore water pressure during an earthquake and prevent liquefaction.

[Brief description of the drawings]

FIG. 1 is a vertical sectional view of a shield tunnel for drainage and a direction perpendicular to the direction, showing one embodiment of the present invention.

FIG. 2 is a horizontal sectional view at a shield tunnel position.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Existing structure, 2 ... Foundation rubble, 3 ... Filling sand, 4 ... Backfill soil, 5 ... Liquefaction suppression ground, 6 ... Tunnel, 7 ... Artificial drain material

──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yujiro Izumoi 1-1-13 Yamashita, Okayama City, Okayama Prefecture Inside Omotogumi Co., Ltd. (72) Inventor Akiyuki Yamamoto 1-1-1, Yamashita, Okayama City, Okayama Prefecture No. 13 Omotogumi Co., Ltd. (56) References JP-A-9-189025 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) E02D 27/34 E02D 3/10 103

Claims (3)

(57) [Claims] 1. A building a tunnel across the lower existing structures in the ground, install the artificial drain material radially to the existing structures just below the soil to be liquefaction deterrence from the tunnel, during an earthquake A method for suppressing liquefaction of an existing structure directly under ground, wherein excess pore water pressure is dissipated through the artificial drain material and the tunnel. 2. The method according to claim 1, wherein the artificial drain material is installed in a hole drilled into a target ground through a tunnel wall using a boring machine. . 3. The method according to claim 1, wherein water collected in the tunnel through the artificial drain material is drained from a shaft.