JP2001355230A - Ground improving method by mixing and stirring - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the strength of an improved ground while avoiding the deterioration of workability. SOLUTION: A ground improving device 32 provided with a stirring shaft 30 having a stirring/mixing vane 28 on the tip side is used in improving the ground 10 by a deep layer mixing process method. When the stirring shaft 30 reaches an improvement depth, the intrusion of the stirring shaft 30 is finished, and its extraction is started. When the stirring shaft 30 is extracted, the slurry including a solidifying agent such as cement is injected into the ground 10 while the stirring/mixing vane 28 is rotated, and ground sediment and the slurry are mixed and stirred. When the solidifying agent mixed and stirred with the ground sediment is solidified as time elapses, the columnar improved body 20 solidified with the ground sediment is created. The slurry including the cement mixed and stirred with the ground sediment has the water- cement ratio below 60%, and it is added with a viscosity reducing agent and the solidifying agent of 4 KN or above per unit volume of the slurry.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for improving ground by mixing and stirring such as a deep mixing method.

[0002]

2. Description of the Related Art Various methods for improving soft ground have been developed and put to practical use. As one type of such ground improvement, a cement-based solidifying material such as cement or lime is supplied as slurry to the ground to be improved, and the ground soil and the solidified material are mechanically mixed and stirred in situ with a stirring blade or the like. There is known a deep mixing method in which soft soil is solidified to form an improved body having a predetermined shape in the ground.

[0003] In such a ground improvement method, it is also known that the strength characteristics of an improved body formed in the ground greatly depend on the soil properties of the ground. Generally, there is a tendency for the strength to decrease in the order of sand, sandy silt, silt, clay, Kanto loam, and organic soil.

[0004] The strength of the improved body formed by the deep mixing method greatly differs depending on the difference in soil quality, and is one-fifth that of the high-pressure jet stirring method for discharging and replacing the in-situ soil.
The value is as low as about 1/10, and there is a technical problem as described below when trying to further increase the strength.

[0005]

In order to achieve high strength in sand, silt, clay and Kanto loam excluding organic soil such as humus by the deep mixing method, for example, cement or cement-based solidification is required. It is conceivable to increase the addition amount of the material, but if the amount of the solidifying material is increased, the viscosity of the slurry increases, and the workability deteriorates,
In some cases, mixing and agitation become difficult or predetermined kneading cannot be performed, which causes another problem that strength is insufficiently developed and becomes non-uniform.

For this reason, in the conventional deep mixing method, the amount of the solidified material to be used is set to 1.0 KN to 3.0 KN / m.
³ , and the water-cement ratio was set to about 60 to 120% in order to secure workability.

SUMMARY OF THE INVENTION The present invention has been made in view of such conventional problems, and an object of the present invention is to provide a conventional low strength improvement effect while avoiding a decrease in workability. It is an object of the present invention to provide a ground improvement method by mixing and stirring, which can ensure a sufficient improvement effect on a damaged formation.

[0008]

In order to achieve the above object, the present invention provides a method for mixing and stirring a soil containing soil and a slurry containing a solidifying material such as cement at a current position and mixing the soil in the ground. In a ground improvement method for solidifying earth and sand with the slurry to form an improved body having a predetermined shape, the slurry has a water cement ratio of less than 60%, a viscosity reducing agent is added, and the solidified material is removed. 4 KN or more was added per unit volume. According to the ground improvement method by mixing and stirring configured as described above, the water-cement ratio of the slurry is less than 60% and the solidified material is added at 4 KN or more per unit volume, so that the improved body formed in the ground Is higher than that of the high-pressure jet stirring method.
In this case, if the water-cement ratio of the slurry is less than 60%, the viscosity of the slurry is increased, and there is a concern that the workability may be reduced. However, in the present invention, since the viscosity reducing material is added to the slurry, the solidified material increases. As a result, a decrease in workability due to an increase in viscosity can be avoided. More specifically, the water-cement ratio of the slurry can be set to 40%, which is less than 60%. As shown in FIG. 4 described below, the amount of the viscosity reducing agent can be set so that the viscosity of the slurry becomes 2000 CP or less when the standing time is about 1 hour. According to this configuration, even if the water cement ratio of the slurry is about 40%, the workability equivalent to the conventional construction method in which the water cement ratio is 60% or more can be secured.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG.
Shows an embodiment of the ground improvement method by mixing and stirring according to the present invention.

The ground improvement method shown in FIG. 1 illustrates a case where the present invention is applied to a deep mixing treatment method. When the ground 10 is improved by the deep mixing method, a ground improvement device 32 having a stirring shaft 30 provided with a stirring and mixing blade 28 at the tip end is used.

The stirring shaft 30 is mounted on a drive mechanism 36 which is vertically movably supported by a reader 34, and has a supply passage for slurry containing cement therein. When constructing the improved body 20, first, FIG.
As shown in (A), the positioning of the stirring shaft 30 is performed.

When the stirring shaft 30 is positioned and its verticality is confirmed, the stirring shaft 30 is rotated while the stirring shaft 30 is rotated.
0 is penetrated to the depth where the ground improvement is required (see FIG. 1 (B)).

When the agitating shaft 30 penetrates, the solidifying material is not injected, but compressed air is injected from the injection port provided in the stirring and mixing blade 28 to prevent the injection port from being clogged. Then, when the stirring shaft 30 reaches the improved depth, the penetration of the stirring shaft 30 is finished, and the stirring shaft 30 starts to be pulled out (FIG. 1).
(See (C) and (D)).

When the stirring shaft 30 is pulled out, a slurry containing a solidifying material such as cement is injected and supplied into the ground 10 while the stirring and mixing blades 28 are rotated, and the soil and the soil at the site are mixed and stirred. .

Then, when the solidified material contained in the slurry mixed and stirred with the on-site soil is solidified with the passage of time, a columnar improved body 20 which solidifies the on-site soil is created (FIG. 1 (D)). )reference).

In the deep mixing method, a stirring shaft 30 is used.
There are a type in which the solidified material is injected at the time of penetration and a type in which the material is injected at the time of lifting. In the present embodiment, the latter is exemplified, but the former type does not pose any problem.

The basic structure of the above-described deep mixing processing method is the same as that of the conventional method of this type. However, the method of this embodiment has the following remarkable features. That is, in the case of the present embodiment, the slurry containing a solidifying material such as cement mixed and stirred with on-site soil and sand has a water-cement ratio of less than 60%, a viscosity reducing agent is added, and the solidification is performed. The material is added at 4KN or more per unit volume.

When the slurry having such a structure is used, the water-cement ratio is reduced to less than 60%. Therefore, if the water content is the same, the amount of added cement or cement-based solidifying material increases, and as a result, The strength of the improved body 20 formed therein increases.

In this case, the water-cement ratio of the slurry is 60
%, There is a concern that the viscosity of the slurry will increase and the workability will decrease. However, in this embodiment, since the viscosity reducing agent is added to the slurry, the decrease in the workability due to the increase in viscosity is avoided. be able to.

The amount of the viscosity reducing agent can be set, for example, so that the viscosity of the slurry becomes 2000 CP or less after about one hour of standing time. This is equivalent to the workability equivalent to that of the conventional method of setting up to 120%.

FIGS. 2 to 4 show the results of experiments conducted to confirm the effects of the present invention. 2 and 3 show the results of a strength test of the improved body using a slurry having a water-cement ratio of 40% or less according to the present invention. FIG. 2 shows a material age of 28 days, and FIG. It is a measurement result of 90 days old uniaxial compressive strength.

In the strength test of the improved body,
. JIS R5210 ordinary Portland cement (N
),. JIS R5211 blast furnace cement type B (referred to as BB),. Cement-based solidifying material 1 (manufactured by Sumitomo Osaka Cement Co., Ltd., Tough Lock B, trade name, referred to as TLB),. Cement-based solidifying material 2 (manufactured by Taiheiyo Cement Corporation, Geoset 23, trade name, referred to as GS23),. Cement-based solidifying material 3 (manufactured by Taiheiyo Cement Corporation, Geoset new, trade name, GS new),.
Cement-based solidifying material 4 (manufactured by Ube Mitsubishi Cement Co., Ltd., Eustavir 30, trade name, US30);
Cement-based solidifying material 5 (manufactured by Taiheiyo Cement Corporation, Geoset A, trade name, referred to as GSA); Cement-based solidifying material 6 (manufactured by Taiheiyo Cement Corporation, Geoset B,
Eight types were prepared.

In this embodiment, what is referred to as a cement-based solidifying material is a general term for a mixture of cement, a pozzolanic substance such as slag and fly ash, and an inorganic compound such as sulfuric acid and calcium chloride. It is.

The soil material corresponding to the on-site soil is:.
sand,. Silt,. clay,. Four types of ROHM were prepared.

The addition amount of each solidifying material was 5.0 KN / m ³ , and the water cement ratio was 40%. Then, a slurry of 18N viscosity reducing agent (proto powder,
(Trade name, manufactured by Mitsubishi Rayon Co., Ltd.).

The preparation of the specimen is in accordance with JGS T821 “Method of preparing specimen without compaction of stabilized soil”, and the strength test is based on JIS A1216 “Uniaxial compression test method of soil”.
Performed in accordance with

As is clear from the strength test results shown in FIGS. 2 and 3, the soil to be improved except for the loam, and by selecting a solidifying material for each of sand, silt, and clay, 10N / It was confirmed that a uniaxial compressive strength of not less than mm ² was obtained.

In the conventional deep mixing method, the magnitude of the uniaxial compressive strength is 0.1 to 0.4 N / mm in onshore construction.
^2, a value of more than 2 times the design strength, which has been a 0.5~2.5N / mm ² at sea construction, also, the design strength criteria for high-pressure injection mixing method, the sandy soil 1.0 ~ 3.0 N / m
It was confirmed that both values were larger than m ² and 1.0 N / mm ² of the cohesive soil.

FIG. 4 shows a measurement result obtained by measuring a temporal change in viscosity when a viscosity reducing agent is added to a slurry containing a solidifying material such as cement of the present invention. In this viscosity test, proto powder (trade name, manufactured by Mitsubishi Rayon Co., Ltd.) was used as a viscosity reducing agent.

Normal Portland cement was used as a solidifying material for the slurry, and the water cement ratio was set to 40%. The addition amount of the viscosity reducing agent was set as shown in the following table.
In this viscosity test, the viscosity of the slurry to which the viscosity reducing agent was not added was also measured for comparison.

[0031]

[Table 1]

Each slurry was prepared using a cement mixer with the composition shown in Table 1, and the stirring time was 3 minutes. Then, the viscosity was measured with a B-type viscometer over time.

FIG. 4 shows the results of a viscosity test when proto powder is used as the viscosity reducing agent. As is clear from the results shown in FIG.
The addition in the range of ~0.10KN / m ^3, even water-cement ratio be 40% in 1 hour before and after standing time,
It was found that the viscosity of the slurry was about 2000 CP.

The viscosity of about 2000 CP is such that the water-cement ratio without adding the viscosity reducing agent shown in FIG.
Is equivalent to the slurry in the standard specification of the indoor mixing test of the conventional deep mixing method, and the water-cement ratio is 60 to 120.
%, And it was confirmed that when the viscosity was about 2,000 CP, the workability equivalent to that when the water cement ratio was 60% could be secured.

In the above-described embodiment, the case where the columnar improved body 20 is formed in the ground 10 has been exemplified. However, the present invention is not limited to this.
It can also be applied to a ground improvement method of forming an improved body of another shape such as a wall shape, a lattice shape, a block shape, or the like by forming adjacently.

[0036]

As described above in detail in the embodiments,
According to the ground improvement method by mixing and stirring according to the present invention,
While avoiding a decrease in workability, a sufficient improvement effect can be ensured even for a stratum in which only a low-strength improvement effect can be ensured conventionally.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a construction step showing one embodiment of a ground improvement method by mixing and stirring according to the present invention.

FIG. 2 is a graph showing measured values of uniaxial compressive strength at a material age of 28 days when a slurry used in the soil improvement method according to the present invention is applied to various types of soil.

FIG. 3 is a graph showing measured values of uniaxial compressive strength at 90 days of age when a slurry used in the soil improvement method according to the present invention is applied to various types of soil.

FIG. 4 is a graph showing a measured value of a change over time in viscosity when a viscosity reducing agent is added to a slurry used in the ground improvement method according to the present invention.

[Explanation of symbols]

 10 ground 20 improved body 32 ground improvement device

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Hiroshi Wada 2-15-2 Konan, Minato-ku, Tokyo Obayashi Gumi head office (72) Inventor Nobunaga Ino 2-2-15-2 Konan, Minato-ku, Tokyo Obayashi Gumi head office (72) Inventor Noriaki Tanaka 2-1-2-2 Konan, Minato-ku, Tokyo Obayashi Gumi head office (72) Inventor Fumiyuki Yokomizo 2-15-2 Konan, Minato-ku, Tokyo Obayashi head office (72) Inventor Hiroyuki Nishigami 2- 15-2 Konan, Minato-ku, Tokyo Obayashi Gumi Corporation (72) Inventor Yoshimi Hosoya 2- 15-2 Konan, Minato-ku, Tokyo Obayashi Gumi Corporation (72 Inventor Tatsuyuki Matsuo 4-640 Shimoseito, Kiyose-shi, Tokyo F-term in Obayashi Corporation Technical Research Institute, Inc. (Reference) 2D040 AA01 AB05 AC02 AC04 BB01 BD05 CA01 CA03 CB03

Claims (3)

[Claims] 1. An on-site soil and a slurry containing a solidifying material such as cement are mixed and stirred at a current position to solidify the on-site soil with the slurry in the ground to form an improved body having a predetermined shape. In the soil improvement method, the slurry has a water cement ratio of less than 60%,
A ground improvement method by mixing and stirring, wherein a viscosity reducing agent is added and the solidified material is added in an amount of 4 KN or more per unit volume. 2. The slurry has a water-cement ratio of 40%.
The ground improvement method by mixing and stirring according to claim 1, characterized in that: 3. The method for improving ground by mixing and stirring according to claim 1, wherein the amount of the viscosity reducing agent is set so that the viscosity of the slurry is 2000 CP or less.