JP2001115444A - Ground improvement method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ground improvement method which is most effective to both a liquefaction ground on a surface layer part and a soft ground therebelow. SOLUTION: The liquefaction ground 1 is improved to a degree that generation of liquefaction can be suppressed, and the soft ground 2 below the liquefaction ground 1 is improved to a degree that the settlement is suppressed, and the load from the liquefaction ground 1 can be sustained. In particular, for the improvement of the soft ground 1, a solidification body 5 of high strength is prepared in a wall continuous in two directions (in a plane-lattice). In addition, a solidification slab 6 is prepared in a boundary part between the liquefaction ground 1 and the soft ground 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a soil improvement method, and more particularly to a liquid ground in a surface layer where sand or volcanic ash is liable to liquefy and a soft ground where a clay or silt is liable to sink below. It is done for.

[0002]

2. Description of the Related Art Generally, in order to use a soft ground such as a sandy ground which is likely to be liquefied or a viscous ground which is inevitable for a long-term consolidation settlement as a foundation ground for a structure, it is necessary to improve the ground to a stable ground in advance. is there.

Heretofore, as this kind of ground improvement method, for example, a deep layer mixing method in which a scientific stabilizer such as lime or cement is added to the ground to a deep portion and forcibly mixed with excavated soil is used. Using a compaction method, impact or vibration to consolidate the entire ground, placing sand piles in the ground, and compacting the soft ground with a sand compaction pile that creates a group of well-sealed sand piles The compaction method and the drain method, which installs multiple drains made of sand piles etc. in the ground to shorten the drainage distance of soil water and promote consolidation and improve bearing capacity, are widely known. I have.

[0004]

However, the consolidation method is
Although the most reliable construction can be expected, it consumes a large amount of stabilizers such as cement and needs to be performed over a wide range.

Although the compaction method has a low construction cost, it cannot completely suppress the occurrence of liquefaction at the time of a large earthquake such as a level 2 earthquake, and when a large amount of natural sand is used as a compaction material. It is not desirable for preserving the natural environment.

[0006] In the drain method, when the target ground is a low-permeability cohesive soil layer or the like, there is naturally a limit in short-term acceleration of settlement and improvement in bearing capacity, and a considerable period is required until the ground becomes stable. Cost. In addition, high costs and long construction periods are inevitable.

Further, in the case of Japan, especially in the landfill area in the coastal area or in the inland area, the surface layer is a ground where sand and volcanic ash such as volcanic ash are likely to be liquefied, and the deeper layer below the ground is made of clayey soil or silt. It is often formed on soft ground that cannot escape consolidation settlement for a long time.

[0008] Even if the ground improvement is performed on such ground by the above-described single method, even if it is effective for one ground, it is not necessarily effective for the other ground. There was a problem that it was impossible to make reliable and reliable ground improvement.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and provides a ground improvement method which is particularly effective for liquefied ground in the surface portion and soft ground below which unconsolidation has not been completed. Is the subject.

[0010]

According to a first aspect of the present invention, there is provided a soil improvement method for a liquefied ground and a soft ground below the liquefied ground. In the construction method, liquefied ground is improved to a level that can suppress the occurrence of liquefaction, and subsidence can be suppressed for soft ground below liquefied ground, or from liquefied ground. Improve the ground to a strength that can support the load.

According to a second aspect, in the ground improvement method of the first aspect, a plurality of high-strength solidified bodies scattered in a wall shape or a column shape continuous in one or two directions are formed as a soil improvement for a soft ground.

According to a third aspect of the present invention, in the ground improvement method according to the second aspect, the high-strength solidified material is removed from the liquefied ground with respect to the supporting ground below the soft ground or both the supporting ground and the liquefied ground. Continuously forming to a predetermined depth.

According to a fourth aspect, in the ground improvement method of the first, second or third aspect, a high-strength solidified ground is formed at a boundary between the liquefied ground and the soft ground. According to a fifth aspect, in the ground improvement method according to the first, second, third, or fourth aspect, the solidified milk and the excavated soil are applied to the liquefied ground and the soft ground by high-pressure injection of the solidified milk and rotation of the stirring rod. And improve the ground by mixing and mixing.

[0014]

1 to 6 show an example of the present invention. In the drawings, the ground for which the ground is to be improved is ground which is liable to cause liquefaction of sand, volcanic ash, etc. (hereinafter referred to as "liquefied ground"). 1), and a deep portion below the liquefied ground 1 has a ground (hereinafter referred to as a “soft ground 2”) that cannot escape long-term consolidation such as a viscous soil or silt. There is a supporting ground 3 below.

The liquefied ground 1 has such a strength that the occurrence of liquefaction can be suppressed.
At about 80665 × 10 ⁴ Pa), the ground improvement is performed on the entire liquefied ground 1. The ground obtained by improving the liquefied ground 1 in this manner is referred to as a low-strength solidified ground 4.

On the other hand, with respect to the soft ground 2, strength enough to prevent long-term consolidation settlement, strength enough to withstand the load transmitted from the low-strength solidified ground 4, or long-term consolidation settlement is suppressed and low. The ground is improved so as to have a strength that can withstand the load transmitted from the hardened ground 4.

Also, for example, a wall shape continuous in one direction (see FIGS. 3 and 4), a wall shape continuous in two directions (planar lattice shape) (see FIG. 1), or evenly over the whole The ground is partially improved in the form of columns (see FIGS. 5 and 6) scattered in the area.

A predetermined depth (see FIGS. 3, 4, 5) until the lower ground 3 is securely reached (see FIGS. 1 and 2) or continuously from the soft ground 2 with respect to the support ground 3. Alternatively, the ground improvement section of the soft ground 2 (referred to as a later-described high-strength section) may be continuously improved by a predetermined depth (see FIG. 6) from the soft ground 2 to both the support ground 3 and the low-strength solidified ground 4. Strength solidified body 5) and supporting ground 3 or supporting ground 3
And integration with the low-strength solidified ground 4. Thus,
A part obtained by improving a part of the soft ground 2 is referred to as a high-strength solidified body 5.

The strength, thickness, diameter,
The form such as the interval is determined by examining the geological condition of the soft ground 2 and the like. For example, FIG. 1 and FIG.
FIG. 3 and FIG. 4 show an example in which a plurality of high-strength solidified bodies 5 are continuously formed in a plane lattice-like wall shape. And support ground 3
2 shows an example in which the ground is continuously formed from the soft ground 2 to a predetermined depth.

FIG. 5 shows an example in which the high-strength solidified bodies 5 are uniformly scattered in a columnar shape as a whole, and are continuously formed from the soft ground 2 to the support ground 3 to a predetermined depth. It is shown.

FIG. 6 shows that the high-strength solidified body 5 is uniformly scattered in a columnar shape as a whole, and the supporting ground 3 and the low-strength solidified ground 4
2 shows an example in which both of the grounds are continuously formed from the soft ground 2 to a predetermined depth.

In any of the examples, a connection solidified body (not shown) for integrally connecting a plurality of high-strength solidified bodies 5 adjacent to an intermediate portion of the high-strength solidified body 5 is in the form of a plate, beam, or brace. May be provided.

Further, if necessary, a high-strength solidified plate 6 for uniformly distributing and transmitting a load from the low-strength solidified ground 4 to the high-strength solidified body 5 at the boundary between the liquefied ground 1 and the soft ground 2.
Is formed integrally with the low-strength solidified ground 4 and the high-strength solidified body 5. The high-strength solidified plate 6 is formed to have a strength equal to or higher than that of the high-strength solidified body 5. FIG.
(A) and (b) show an example thereof.

It should be noted that the liquefied ground 1 is
A method for improving a part of the soft ground 2 into a high-strength solidified body 5 and forming a high-strength solidified bed 6 at a boundary between the liquefied ground 1 and the soft ground 2 includes a high-pressure injection method,
In addition to the high-pressure injection / mechanical stirring method, the deep mixing method, and the like, there is a chemical liquid injection method of solidifying the formation by injecting (grouting) a chemical liquid such as cement milk or water glass into the ground.

At this time, when the deep mixing method is used,
The amount of additive (solidifying material) such as cement is appropriately changed so that the strength can be improved to a predetermined value for each appearance depth. In addition, the ground improvement is repeatedly performed while appropriately wrapping the columnar improvement.

In particular, in the case of performing the method by a combination of high-pressure injection and mechanical stirring, for example, as shown in FIGS. 7A to 7E, the pressure, discharge amount, compounding,
By changing the casting speed, or by manipulating the position, angle, etc., of the cement milk discharge port of the high-pressure injection unit and the mechanical injection unit, and by appropriately changing the mixing of the cement milk, When improving soft ground, the diameter and strength of the improved soil can be arbitrarily changed by one casting, and low-cost construction is possible.

For example, in the example shown in FIG. 7A, a high-strength improved mechanical stirrer 5a is formed on the soft ground 2 by mechanical stirring, and high-pressure injection is performed outside the high-strength improved mechanical stirrer 5a. The high-strength improved high-pressure injection part 5b is formed.

For the liquefied ground 1, a low-strength improved mechanical stirrer 4a is formed continuously from the high-strength improved mechanical stirrer 5a by mechanical stirring, and a low-strength improved high-pressure jet is applied to the outside thereof by high-pressure injection. The portion 4b is formed.

Further, a high-strength mechanical stirrer 5c is formed continuously from the high-strength mechanical stirrer 5a to a predetermined depth with respect to the liquefied ground 1. In this way, the high-strength improved mechanical stirrers 5a and 5c and the high-strength high-pressure jetting unit 5b are formed one or several times and integrally formed in the lateral direction, thereby forming a columnar high-strength solidified body 5 having a predetermined diameter. Also, by being formed continuously in the horizontal direction, the high-strength solidified body 5 having a wall shape having a predetermined thickness is obtained.

Further, the low-strength solidifying plate 4 is formed by continuously forming the low-strength improving mechanical stirrer 4a and the low-strength improving high-pressure jetting unit 4b in four directions. In the example illustrated in FIG. 7B, only the high-strength mechanical stirrer 5 a is formed on the soft ground 2 by mechanical stirring, and the low-strength mechanical stirrer 4 a is formed on the liquefied ground 1. The high-strength high-pressure injection unit 4b is formed, and the high-strength improved mechanical stirring unit 4c is formed to a predetermined depth with respect to the liquefied ground 1.

Further, in the example shown in FIGS. 7 (d) and 7 (e), a high-strength improved high-pressure jetting section 6a is formed at the boundary between the liquefied ground 1 and the soft ground 2 by high-pressure jetting to obtain high strength. The high-strength solidified plate 6 is obtained by continuously forming the improved high-pressure injection portions 6a in all directions.

[0032]

As described above, the present invention suppresses subsidence and liquefaction at a low cost without fail because the shape and strength of the stratum are suppressed to the minimum necessary for each ground. Especially superior to the consolidation method.

The liquefied ground on the surface layer is completely consolidated with the minimum necessary strength, so that liquefaction can be reliably suppressed. In addition, since the ground after improvement consists of low-strength ground on the surface layer and high-strength ground below it, it sinks into the liquefied ground due to the settlement of soft ground that occurs after construction or the structure built on it There is no need to worry about this, and it is better than the compaction method.

[0034] Further, the ground is improved by stirring and mixing the solidified milk and the excavated soil by high-pressure injection of the solidified milk and rotation of the stirring rod. By changing the discharge rate, blending, casting speed, etc., and changing the strength appropriately to continuously improve,
The construction cycle is short, the construction period can be shortened, and economic construction is possible. In this regard, it is superior to the drain construction method.

Further, after a predetermined curing period (about one to four weeks) until the improved ground is hardened after construction,
It can be used and can be used for a short period of time. Furthermore, by providing improved soil at the boundary between the liquefied ground and the soft ground, it is possible to reliably block the rise in excess pore water pressure from the soft ground, and to reliably prevent liquefaction of the low-strength ground, Not only can the ground be stabilized, but a plurality of high-strength members are integrally and rigidly joined via the plate-shaped soft ground, so that it is possible to provide a base ground having extremely high support strength.

In particular, as in the landfill area of Japan's coastal area,
It is suitable for ground improvement of a liquefied ground which is liable to liquefy sand or volcanic ash on the surface layer, and a soft ground which is prone to long-term consolidation such as clay or silt beneath.

[Brief description of the drawings]

FIG. 1 shows a ground improved by the present method, (a) is a longitudinal sectional view, and (b) is a sectional view taken along the line II in (a).

FIGS. 2A and 2B show a ground improved by the present method, in which FIG. 2A is a longitudinal sectional view and FIG. 2B is a sectional view taken along the line II in FIG.

FIGS. 3A and 3B show a ground improved by this method, in which FIG. 3A is a longitudinal sectional view, and FIG. 3B is a sectional view taken along the line II in FIG. 3A.

4A and 4B show a ground improved by the present method, in which FIG. 4A is a longitudinal sectional view, and FIG. 4B is a sectional view taken along the line II in FIG.

FIGS. 5A and 5B show a ground improved by the present method, in which FIG. 5A is a longitudinal sectional view and FIG. 5B is a sectional view taken along the line II-II of FIG.

FIGS. 6A and 6B show a ground improved by the present method, in which FIG. 6A is a longitudinal sectional view and FIG. 6B is a sectional view taken along the line II-II in FIG.

FIGS. 7A to 7E are longitudinal sectional views showing a construction method.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Liquefied ground (ground which tends to cause liquefaction) 2 Soft ground (ground which cannot escape compaction) 3 Supporting ground 4 Low-strength solidified ground (ground formed by improving liquefied ground) 4a Low-strength mechanical stirrer 4b Low-strength improved high-pressure injection unit 5 High-strength solidified body (part formed by improving part of soft ground) 5a High-strength improved mechanical stir unit 5b High-strength improved high-pressure injection unit 5c High-strength improved mechanical stir unit 6 High-strength solidified Plate 6a High-strength improved high-pressure injection unit

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Katsuo Kamada, Inventor 1-14-6 Kudankita, Chiyoda-ku, Tokyo Inside the Urban Infrastructure Development Corporation (72) Inventor Mitsuko Iwata 1-2-7 Moto-Akasaka, Minato-ku, Tokyo Kashima Construction Co., Ltd. (72) Inventor Eizuka Fukasawa 2-9-1-1, Tobita-Shi, Chofu-shi, Tokyo Kashima Construction Co., Ltd. (72) Inventor Hiroshi Hayashi 2-191-1, Tobita-Shi, Chofu-shi, Tokyo Kashima Within the Technical Research Institute of Construction Co., Ltd. (72) Michio Fujita 4-51, Otacho, Naka-ku, Yokohama-shi, Kanagawa Prefecture Within Kashima Construction Co., Ltd.Yokohama Branch (72) Inventor Hiroyuki Yamanaka 1-2-7 Moto-Akasaka, Minato-ku, Tokyo No. Kashima Construction Co., Ltd. (72) Inventor Takemine Yamada 2-9-1-1, Tobita-Shi, Chofu-shi, Tokyo Kashima Construction Co., Ltd. 2D040 AA00 AB05 AC02 AC04 AC05 BD02 BD03 BD05 CA01 CA02 CB03

Claims (5)

[Claims] 1. A soil improvement method for a liquefied ground and a soft ground below the liquefied ground, wherein the liquefied ground is improved to a strength sufficient to prevent liquefaction from occurring, and A soil improvement method characterized in that the soil is improved to a degree that can suppress settlement or support the load from the liquefied ground. 2. The soil improvement method according to claim 1, wherein as the soil improvement for the soft ground, a plurality of high-strength solidified bodies scattered in a wall shape or a column shape continuous in one or two directions are formed. . 3. The method according to claim 1, wherein a high-strength solidified body is continuously formed from the liquefied ground to a predetermined depth on the support ground below the soft ground, or on both the support ground and the liquefied ground. The ground improvement method according to claim 2, wherein 4. The soil improvement method according to claim 1, wherein a high-strength solidified ground is formed at a boundary between the liquefied ground and the soft ground. 5. A soil improvement in which the solidified milk and the excavated soil are agitated and mixed with the liquefied ground and the soft ground by high-pressure injection of the solidified milk and rotation of the stirring rod. The ground improvement method according to claim 1, 2, 3, or 4.