JPH08120661A - Device for ground under existing structure for preventing liquefaction of ground - Google Patents

Abstract

PURPOSE: To easily execute works for providing the ground under an existing structure with means that work for preventing liquefaction of the ground on the occasion of an earthquake. CONSTITUTION: A curved bore is built, starting from a starting point provided to the ground surface 4 on one side of an existing structure 1, to a depth on a stratum 3 to be improved because of its liability to liquefaction. Then, excavation holes 6 are burrowed, starting from the lower end of the curved bore, to the inside of the stratum 3 to be improved, or the underside of the stratum 3, approximately in a straight line in a length extending over the underside of a single or a plurality of existing structures, and works for providing the ground with means for preventing liquefaction are executed, using the excavation holes 6.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for preventing liquefaction of the ground beneath an existing structure. Generally, as a measure for preventing the liquefaction of the ground, the ground is compacted to increase the density. Improve the soil to a non-liquefaction particle size or inject the mixture to solidify. It lowers the groundwater level and increases the effective stress. To quickly dissipate excess pore water pressure generated during an earthquake. It is known that it is effective to form a wall in the surrounding ground to prevent the rise of excess pore water pressure directly below the structure, and to reduce the repeated shear deformation during an earthquake. Among them, in the case of targeting existing structures, there is a case where a method of once moving the structures and taking measures is adopted, but it requires a great deal of construction period and cost.
As a means for solving these problems, some proposals have been made to improve the ground directly under the existing structure.

[0002]

2. Description of the Related Art For example, the conventional structure disclosed in Japanese Patent Laid-Open No. 6-41990 has an existing structure 1 as shown in FIG.
Arc-shaped pilot pipes that reach the opposite side from the surrounding ground 4 through the direct foundation 2 of the existing structure 1 to the opposite side are installed side by side, and the solidified material is discharged from the tip of the pilot pipe while stirring with the ground with a widening bit. By defining the impermeable layer 16 on the immediate foundation of the existing structure and installing a drain hole in the inner ground to drain the water, the groundwater level above the impermeable layer is lowered to increase the pore water pressure. In addition to preventing the liquefaction, the effective stress is increased. In addition, JP-A-63-26880
No. 9 gazette discloses that the ground 4 around the structure as shown in FIG.
From the above to the lower part of the structure 1, an arc-shaped boring hole 17 is excavated by an arc propulsion method, and the boring hole is filled with crushed stone to discharge free water, or a strong material is injected to solidify the ground. Is disclosed.

[0003]

The conventional techniques of these two examples can improve the direct substrate without affecting the structure from the outside of the existing structure 1, but have the following problems. Both of them use arc-shaped propulsion pipes, so they cannot properly deal with layered ground for improvement. That is, as shown in FIG. 14, an unimproved portion 14 is generated because the ground is improved by penetrating the layered improvement target range 3 in an arc shape. In order to reduce the unimproved portion 14 as much as possible, it becomes necessary to increase the radius of curvature of the arc (R ₁ → R ₂ ) (that is, to approximate a straight line). The starting / arriving portion of the propulsion pipe is separated from the existing structure 1. (L ₁ → L ₂ ), useless propulsion must be performed. When attempting to improve the ground by traversing the ground at the bottom of a plurality of existing structures 1 with one propulsion pipe, it is necessary to increase the radius of curvature of the arc 13, and in arc propulsion using the arc pipe, especially in the upward direction. It becomes difficult to control the trajectory. Therefore, as shown in FIG. 15, it is necessary to perform the circular arc propulsion 12 downward from both sides of the existing structure 1 a plurality of times. Further, when the improvement target stratum 3 is at a deep position or even in the large-scale existing structure 1, it is necessary to perform circular arc propulsion with a large radius of curvature, and there are the same problems as described above. The present invention solves the problems of these conventional techniques and can be constructed without a shaft,
It is an object of the present invention to provide a liquefaction prevention device which can surely improve the liquefaction-prone ground layer 3 below a plurality of existing structures 1 and which is advantageous in terms of construction period and cost.

[0004]

In order to advantageously solve the above-mentioned problems, in the ground liquefaction preventing device under the existing structure of the present invention, one ground surface 4 around the existing structure 1 is used. A curved hole is provided from the starting part provided in the ground to the depth of the formation 3 to be improved, which may be liquefied at the time of an earthquake, and the lower end of the curved hole is in the formation 3 to be improved A substantially straight drill hole is bored along the length across the lower part of the structure 1, and liquefaction prevention measures are taken using this drill hole. In addition, a curved hole is provided from the starting portion provided on the ground surface 4 in the vicinity of the existing structure to the depth of the stratum 3 to be improved, which may be liquefied at the time of an earthquake. In or below the stratum 3, a substantially straight drill hole 6 is bored along the length across the ground in the vicinity of the existing structure 1 or a plurality of existing structures 1, and the drill hole 6 is used to prevent liquefaction. The above-mentioned problems can be advantageously solved by applying the above. Further, a water collecting pipe 6a is provided in the excavation hole 6, and a pumping equipment is freely inserted into and taken out from the lowermost end of the water collecting pipe 6a to prevent liquefaction by lowering the groundwater level 7 of the ground below the existing structure 1. The above-mentioned problems can be advantageously solved by taking measures. Furthermore, the above-mentioned problems can be advantageously solved by injecting a chemical or a solidifying material into the surrounding ground from the drilling hole to improve the ground in the stratum having a possibility of liquefaction.

[0005]

Next, the liquefaction prevention device of the present invention is used for the existing structure 1
A curved hole is provided without a shaft from the starting portion provided on one of the ground surfaces around the, and the drilling hole 6 is formed almost linearly along the same from the lower end of the curved hole in the stratum to be improved 3 existing in layers. Drilling, draining from the improvement target formation that has the possibility of liquefaction using this drill hole, lowering the groundwater level or injecting ground improvement liquid such as water glass or cement milk into the improvement target formation 3 Preventive measures are taken to strengthen the ground. That is, in the present invention, the excavation hole for the liquefaction prevention measure in the improvement target formation 3 is made substantially linear along the improvement target formation 3 so that an unmodified portion does not occur. This straight excavation hole is provided under the existing structure of one or more existing structures or over the required length in the adjacent ground, and is connected to the ground surface 4 only on one side to eliminate unnecessary excavation. ing. The curved hole that connects with the straight drill hole functions not only as a vertical hole but also as a conduit in the underground. As a measure against liquefaction, drainage pipes or ground improvement materials will be supplied when lowering the groundwater level.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below with reference to FIGS. 1 to 3 show the first embodiment in which the present invention is applied in the case where a foundation layer of a plurality of existing structures (large-sized cylindrical tank 1) has a stratum 3 with a possibility of liquefaction.
This is an embodiment, and the liquefaction prevention measure is to pump up groundwater by means of the water collection pipe 6 having a relatively small size. In this embodiment, as shown in FIG. 1, two large cylindrical tanks (existing structures) 1 which are already installed have a space B on one ground surface 4 where there is no obstacle as shown in the plan view of FIG. From the starting portion provided apart from each other, a circular arc-shaped tube 5 having a radius R is buried by about 1/4 round by circular arc-shaped propulsion without using a vertical shaft. A straight excavation hole 6 is provided slightly upward in the stratum 3 to be improved over a length that traverses the lower portion of the two large cylindrical tanks 1 from the outlet of the arc pipe 5 (curved hole). Many water collection holes 6b on the wall
A water collecting pipe 6 having a
That is, as shown in FIG. 3, the pumping equipment 8 is inserted into the outlet portion of the arc pipe 5, and the groundwater permeated into the water collection pipe 6 is pumped up to lower the groundwater level to prevent liquefaction. .

The arc tube 5 plays a role of a guide for linearly propelling the water collection tube 6 at a predetermined depth without a vertical shaft. The arc tube is formed into an arc shape by a jack or other propulsion device installed on the ground. It is promoted and installed. This circular arc propulsion method is disclosed in Japanese Patent Laid-Open No. 61-056756, and therefore its detailed description is omitted. The water collection pipe 6 buried in the formation 3 to be improved is a straight pipe having a large number of water collection holes 6b in the pipe wall, and is pushed through the arc pipe 5 by a propulsion device provided on the ground. At this time, although it is forcibly bent into a curved shape inside the arc tube 5, it has to be restored linearly when discharged from the lower end outlet of the arc tube 5.

Therefore, the radius of curvature R of the arc tube 5 is set so that the bending stress of the water collection tube 6 in the arc tube is within the elastic range.
Need to be defined. In this way, the water collection pipe 6 is composed of the straight line portion and the curved portion 6a in the arc pipe 5. When the thrust force of the water collecting pipe 6 is insufficient only by the pushing force of the ground propulsion device, a publicly known excavation method in which a water jet or an excavation cutter is provided at the tip is also used. When the water collection pipe 6 is used as a liquefaction prevention measure as in the first embodiment, the water collection pipe 6 is buried in the improvement target stratum 3 or below the improvement target stratum 3 and the outlet of the arc pipe 5. It is better to point slightly upward from (the position where the curve changes to a straight line).
In this way, the lowermost end of the water collection pipe 6 becomes close to the starting portion, and it becomes easy to insert the equipment 8 for pumping the groundwater collected by the water collection pipe 6.

The arc pipes 5 and the water collection pipes 6 as described above are buried in the required number of formations 3 in the lower part of the existing structure 1 at intervals B. The burying interval B of the water collection pipe 6 is determined in consideration of the subsidence of the existing structure 1, the hydraulic conductivity of the ground, and the like. That is, if a means for lowering groundwater is used as a liquefaction prevention measure as in this embodiment, some ground subsidence may occur due to the decrease in groundwater. Therefore, existing structure 1
If the water collecting pipe 6 buried below the space is too wide, or if it is placed asymmetrically, when pumping up the groundwater, the height difference of the groundwater level becomes large or flat, and the existing structure In order to cause unequal subsidence at 1, the water collecting pipes 6 of relatively small diameter are buried in narrow spaces at equal widths so that the height difference of the lowered groundwater level is minimized. Is.

Next, a second embodiment of the present invention will be described. 5 and 6 show a second embodiment,
This is an example in which the water collecting pipe 6 having a relatively large size is used, the interval B is widened, and the water collecting pipe 6 is provided in the vicinity of the ground so as to avoid immediately below the tank. In the case of the second embodiment, since it can be applied to the ground having a relatively large hydraulic conductivity and the small-scale existing structure 1,
Highly economical. In the second embodiment, since the water permeability is large, as shown in FIG. 6, even if the hole interval B is widened and a water collecting pipe is provided in the ground in the vicinity of the tank to avoid directly below the tank, the groundwater directly below the tank can be collected. Moreover, immediately below the tank, the groundwater level surface 7a, which has decreased from the original groundwater level height 7, becomes almost horizontal,
Does not cause uneven settlement in the ground below the tank. Further, in the case of the second embodiment, the number of excavations can be reduced as compared with the first embodiment, so that there is also an advantage that the construction cost can be suppressed. However, in the case of the second embodiment, it is necessary to increase the amount of pumped water per water collection pipe as compared with the first embodiment. The construction procedure and the method of preventing liquefaction by pumping up groundwater are the same as those in the first embodiment, and therefore the description thereof will be omitted. Whether to adopt the method of the first embodiment or the second embodiment is determined in consideration of various conditions such as the expected ground subsidence amount, the hydraulic conductivity, and the difficulty of excavation. Further, although the water blocking wall is not provided in the first and second embodiments, if the ground around the structure has a space, it is possible to install the water blocking wall to improve the pumping efficiency. Is.

FIGS. 7 to 10 show a third embodiment of the present invention, in which a directional excavation method is used as a means for providing a straight drill hole 6 in the formation to be improved 3 below the existing structure 1 without using a shaft. Used. If there is an obstacle in the outer periphery close to the existing structure 1, if there is an open space at a slightly distant point, or if the formation to be improved 3 is deep, a straight pipe without using the arc-shaped curved pipe as described above. It is possible to apply a directional propulsion method for propelling while controlling the desired orbital shape while directly bending. In this case, the radius of curvature becomes larger than that of the arc-shaped propulsion. For this directional propulsion method, for example, what is carried out by Nippon Steel Corporation called "Arc-cone advance method (PLAD method)" can be applied. This construction method applies the technique of slant digging for oil drilling to the laying of buried pipes. The tip 10 of the pilot pipe is gently slanted as shown in Fig. 8, and the hydraulic motor is driven by using muddy water. Controls the desired orbit while monitoring the orbit with, and can perform vertical and horizontal curves and direct propulsion.

Further, as shown in FIG.
"Flow molding method" that controls the propulsion direction by excavating a water jet with a water jet (Flow molding company)
May be used. In this embodiment, as a liquefaction prevention measure, unlike the first and second embodiments, means for strengthening the ground is shown. Therefore, it is preferable that the excavation hole 6 penetrating the improvement target formation 3 is provided in the middle of the formation to inject the soil improvement material in all directions with respect to the ground around the excavation hole 6. As the ground improvement material, a known material such as a chemical liquid such as water glass or a cement-based solidifying material may be used. As for the injection means, as shown in FIG. 10, an injection tube 11d having a double packer 11a is inserted into a tube body 11 having a hole 11c covered with a sleeve 11b, and the injection tube 11d is moved while performing limited injection. Any method can be used.

It is also possible to apply the method of solidifying the ground to the first and second embodiments as in the third embodiment, and to lower the groundwater level in the third embodiment. It is also possible to apply the method. In addition,
Injection pipe 11 or water collecting pipe 6 in the first embodiment
As shown in FIG. 11, when a slit hole 6c is provided as shown in FIG. 11, the bending rigidity can be weakened and the curved hole can be smoothly propelled. In this case, when the slit holes 6c are arranged in a zigzag pattern, the resistance against thrust is reduced less.

[0014]

According to the present invention, it is possible to easily and effectively take the measures for preventing the liquefaction of the existing structure foundation board, which has not been effective means in the past, without removing or transferring the existing structure. In addition, it is possible to construct without a vertical shaft, and it is possible to surely improve the strata with the possibility of liquefaction under multiple existing structures,
Moreover, the construction period can be shortened and the cost can be reduced. In addition, liquefaction prevention measures include a method of lowering the groundwater level by embedding a water collection pipe in the drill hole and pumping up, or strengthening or reforming the target stratum by chemical injection or injection of solidification liquid from the drill hole. You can also

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional side view showing a curved pipe applied to excavation of a curved portion in a first embodiment of the present invention.

FIG. 2 is a plan view of a portion shown in FIG.

FIG. 3 is a vertical cross-sectional side view showing a state in which pumping equipment is installed at the outlet of an arc tube.

FIG. 4 is a cross-sectional view taken along the line AA of the portion shown in FIG.

FIG. 5 is a plan view showing a second embodiment of the present invention.

6 is a cross-sectional view taken along the line CC of FIG.

FIG. 7 shows a third embodiment of the present invention and is a partially longitudinal side view showing an example in which a directional excavation method is used for excavating a curved portion.

FIG. 8 is a side view showing a state of a tip end portion of the directional excavation pilot pipe.

FIG. 9 is a side view showing a state of a tip end portion of another example of the directional excavation pilot pipe.

FIG. 10 is a partially cutaway vertical side view of an injection tube having a double packer inside a perforated tube.

FIG. 11 is a side view showing an example in which a slit hole is provided in the pipe axis direction of the injection pipe or the water collection pipe to weaken the rigidity.

FIG. 12 is a partially longitudinal side view showing an example in which measures against liquefaction of the ground are taken by the conventional technique.

FIG. 13 is a partial vertical cross-sectional side view showing an example in which measures against liquefaction of the ground are taken by a conventional technique.

FIG. 14 is a partial vertical cross-sectional side view for explaining a problem of a conventional liquefaction countermeasure example.

FIG. 15 is a partial vertical cross-sectional side view for explaining a problem of a conventional liquefaction countermeasure example.

[Explanation of symbols]

 1 Existing structure (tank) 2 Foundation ground 3 Highly liquefiable stratum 4 Ground surface 5 Curved pipe 6 Excavation hole (collection pipe or injection pipe) 6a Bent portion of water collection pipe or injection pipe 6b Water collection pipe or injection pipe Hole in the pipe wall 6c Hole in the pipe wall of the water collection pipe or the injection pipe 7 Original groundwater level surface 7a Lowered groundwater level surface 8 Pumping pump 9 Propulsion machine 10 Tip of directional pilot pilot pipe 11 Pipe 11a Double packer 11b Rubber sleeve 11c Injection hole 11d Injection pipe 12 Arc excavation hole 13 Arc excavation hole 14 Unimproved part of ground to be liquefied 15 Vertical water blocking wall 16 Impermeable layer 17 Arc-shaped boring hole

Front page continuation (72) Inventor Takeshi Tatsuhara 2-6-3 Otemachi, Chiyoda-ku, Tokyo Within Nippon Steel Corporation (72) Takuya Saito 2-3-6 Otemachi, Chiyoda-ku, Tokyo Within Nippon Steel Co., Ltd. (72) Inventor Kunio Nishi, 5-8 Kita-Aoyama, Minato-ku, Tokyo Stock company Intra-company group (72) Inventor Mikio Ohashi 2--5-8 Kita-Aoyama, Minato-ku, Tokyo Stock society Intra-company group (72) Inventor Toshiaki Kato 2-5-8 Kitaoaoyama, Minato-ku, Tokyo Stock company Inter-company group

Claims (4)

[Claims] 1. A curved hole is provided from a starting portion provided on one ground surface 4 around an existing structure 1 to a depth of a stratum 3 to be improved which may be liquefied during an earthquake, and a lower end of the curved hole is formed. A straight line excavation hole 6 in the stratum 3 to be improved or below the same over a length crossing the lower part of the existing structure 1 or a plurality of existing structures 1, and utilizing this excavation hole 6, A liquefaction prevention device for the ground below the existing structure, which is characterized by taking liquefaction prevention measures. 2. A curved hole is provided from the starting portion provided on the ground surface 4 near the periphery of the existing structure to the depth of the stratum 3 to be improved which is likely to be liquefied in the event of an earthquake. From the lower end of this curved hole In or below the stratum 3 to be improved, a substantially straight drill hole 6 is bored over a length across the ground in the vicinity of the existing structure 1 or a plurality of existing structures 1. A liquefaction prevention device for the ground below the existing structure, characterized by taking liquefaction prevention measures. 3. A water collecting pipe 6a is provided in the excavation hole 6, and a pumping equipment is freely inserted into and taken out from the lowermost end of the water collecting pipe 6a.
The liquefaction prevention device for the ground below the existing structure according to claim 1 or 2, wherein a liquefaction prevention measure for lowering the groundwater level 7 of the ground below the existing structure 1 is taken. 4. The existing structure according to claim 1 or 2, wherein a chemical or a solidifying material is injected into the surrounding ground from the excavation hole 6 to improve the ground of the stratum 3 which is likely to be liquefied. Liquefaction prevention device for the ground below.