JPH01142118A - Improving work of low-strength regulating ground - Google Patents

Abstract

PURPOSE:To lessen the variation of strength by a method in which an improved ground is formed by mixing the ground soil with a stabilizer containing calcium carbonate with stirring. CONSTITUTION:The ground soil is mixed with a stabilizer prepared by adding calcium carbonate to ordinary Portland cement to form improved ground. The improved ground is formed for securing the stability of sheathing 30. The low- strength improved ground suitable for excavation can thus be stably obtained with lesser variation of strength.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a low-strength adjustment ground improvement method, and particularly to a ground improvement method in which the improved ground becomes a low-strength ground suitable for excavation, etc.

(Prior Art) As is well known, deep mixing methods, pre-mixing methods, etc. are well known as methods for improving soft ground.

In this type of ground improvement method, for example, a cement-based stabilizer and ground soil to be improved are mixed and stirred to improve the strength of the ground.

By the way, recently, excavation of the ground for earth retaining excavation, the ground below the caisson tip when the caisson is sunk into the ground, the ground near the starting shaft of a shield excavator, and the trench hole for a continuous underground wall has been excavated. These grounds are used to facilitate excavation, prevent caissons from settling, safely launch shield excavators, and prevent the walls of trenches from collapsing. may be improved.

Ground improvement performed for such purposes must not only stabilize the ground, but also have sufficient strength to facilitate excavation.

This strength is 5-10 kg f/c in unconfined compressive strength
It is empirically known that - degree is preferable.

Therefore, in the past, in such cases - boat fishing, the strength was reduced by keeping the amount of stabilizer to a small amount, or by adding water or bentonite, but such methods are explained below. There was a problem.

(Problems to be Solved by the Invention) In other words, in the method described above, even if the amount added to obtain the desired strength is determined in an indoor mixing test, it is difficult to improve the low strength without variation in the actual field. It is difficult to determine the amount of addition needed to obtain the soil, and if the amount of addition is outside the appropriate range, the strength of the improved soil may become extremely low, or conversely, the long-term strength may become too high, resulting in the improvement of the soil. There was a problem that the quality of the products varied widely.

This invention was made in view of these conventional problems, and its purpose is to provide long-term stable, low-strength improved soil in the field, in the same manner as the conventional high-strength improvement construction method. The purpose is to provide a low-strength adjustment ground improvement method that can be easily managed by construction method.

(Means for Solving the Problems) In order to achieve the above object, the present invention provides a ground improvement method for preparing improved ground by mixing and stirring ground soil and a stabilizing material, in which the stabilizing material is made of ordinary Portland cement. In particular, excavation is planned after ground improvement, such as earthwork excavation ground, ground under the mouth of a caisson, ground near a shield starting shaft, and continuous underground wall excavation. By adding the calcium carbonate to the ordinary Portland cement to the ground, stable ground suitable for excavation can be maintained for a long period of time.

Practical formulations when applied to this type of improved ground include, for example, in the deep agitation mixing method, the water-cement ratio is 0.6 to 1.5, and the injection rate is 15 to 1.5 per unit volume of ground soil. It is desirable to set it in the range of ~30%.

In this case, when the water-cement ratio is 1.5 or more, the quality of the improved soil is high and compressible, and when the injection rate is 15% or less, the quality of the improved ground tends to vary.

On the other hand, if the water-cement ratio is less than 0.6 and the injection rate is more than 30%, the strength of the improved ground will be more than 10 kgf/cj, or variations will become large, making excavation difficult.

(Example) Hereinafter, an experimental example conducted to confirm the effects of the present invention will be described.

FIG. 1 is an explanatory diagram of the experimental equipment used in this experiment, and the experiment was conducted assuming a deep stirring mixing method.

The experimental device prepares a container 10 with an open top 6, stores ground soil 12 to be improved in this container 10, and arranges a pair of plate-shaped stirring blades 14, 14 at a predetermined interval. In addition, a two-shaft type stirring device is used in which a hollow vibration-shaped stirring shaft 18 with an elliptical stirring blade 16 arranged between these stirring blades 14 is connected with a connecting member 17, and the interval between the stirring shafts 18.18 is set to 26.
The area to be improved by each stirring device is 320.
They were set so that they partially overlapped each other as m+s.

The stabilizing material is supplied to the ground soil 12 through a through hole 19 located approximately in the center of the portion of the stirring shaft to which the elliptical stirring blade 16 is fixed.
was drilled.

FIG. 2 shows the cross-sectional area of the solidified body 20 formed when the ground is improved using the two-shaft stirring device configured as described above.
In the experimental example, sampling was performed at a total of 5a1 locations (■ to ■) at the center position of each stirring shaft 18 and its outer circumference, and the uniaxial compressive strength in the depth direction of each was measured.

Figures 3 and 4 are graphical representations of the compressive strengths of the measured samples ① to ②.

Note that all the unconfined compressive strengths shown in the figure are values after 14 days of age.

FIG. 3(a) is a diagram to which the method of the present invention is applied,
Types A and B shown in the stabilizer column in the same figure use a mixture of ordinary Portland cement and calcium carbonate as the stabilizer, with type A having a mixture ratio of 50:50, and type B using a mixture of ordinary Portland cement and calcium carbonate. The mixing ratio was 70:30, and the water/A and B ratios were each 1 when slurrying these mixtures.

In addition, the injection rate of stabilizer into the ground soil 12 is 2, respectively.
0% and 30% 21W class.

FIG. 4(b) shows the results of measuring the compressive strength of the consolidated body 20 in ground improvement using the conventional method, which was conducted for comparison with the method of the present invention. Using the same equipment and the same sampling positions as above, sampling was carried out at five locations ■' to ■'.

As a stabilizer, only ordinary Portland cement was used, the water/cement ratio was 1, and the injection rate was 7%, 10%,
There were five types: 15%, 20%, and 30%.

As is clear from FIGS. 3(a) and 4(a), lowering the injection rate of the stabilizer reduces the strength of the solid body 20, and conversely, increasing the injection rate increases the strength. ing.

Furthermore, when comparing the center and outer circumference of the stirring shaft 18, it is recognized that the outer circumference is generally smaller than the center, but the difference is due to the difference in the magnitude of the developed strength. Difficult to compare absolute values.

Therefore, in order to clarify the difference, the ratio between the strength at the center and the strength at the outer periphery was determined at each injection rate.

FIG. 3(b) and FIG. 4(b) show this.

As is clear from the results in this figure, in the conventional method shown in FIG. 4(b), the improved strength decreases as the injection rate decreases, but the strength ratio between the center and outer periphery of the solid body 20 decreases. The variation becomes larger.

Conversely, if the injection rate is increased, the variation in strength ratio will be reduced, but the improved strength will become too large, making it unsuitable for subsequent excavation.

On the other hand, in the method of the present invention in which calcium carbonate is mixed as a stabilizer, the variation in strength ratio is small when the injection rate is in the range of 20 to 30%, and the strength does not become too large as in the conventional method.

FIG. 6 shows examples of various types of construction work to which the method of the present invention can actually be applied. In order to ensure stability, this is a method in which the excavated ground within the shoring 30 is improved in advance so that it has low strength using a deep mixing method.

In addition, the same figure (b) shows a method of improving the ground under the cutting edge of the caisson 32 to have low strength by the method of the present invention, and the same figure (c) shows the starting shaft 36 of the shield excavator 34, and the shield excavator 34 is started. This shows what is applied when improving the ground in areas where

Furthermore, FIG. 6(d) shows a method of improving the excavated ground using the method of the present invention before excavation when forming a trench hole 38 by excavating collapsible ground using the continuous underground wall construction method. .

Furthermore, FIG. 6(e) shows that, while the application example described above is a method in which the present invention is applied to a deep no-mixing method, in this example, the present invention is applied to a pre-mixing method; is used to launch a shield tunneling machine, but in order to launch the tunneling machine diagonally from the starting shaft 36 toward the submarine ground 40, earth and sand and calcium carbonate are placed in advance on the submarine ground 40 near the starting shaft 36. This is a method in which an embankment material 42 is prepared by mixing a stabilizer and a stabilizer, and this is placed on the ground 40.

In addition, in the method shown in FIG. 6(e), a caking agent for reducing separation may be added to the stabilizer.

Further, in the above embodiments, the stabilizer is used in the form of a slurry, but for example, in the premixing method, a powder can also be used.

(Effects of the Invention) As explained in detail above, in the low-strength adjustment ground improvement method according to the present invention, a stabilizing material containing calcium carbonate is used for the ground to be improved, so that the low-strength improved ground suitable for excavation is created. , it can be obtained in a stable state with little variation in strength.

In addition, improved ground having such homogeneous strength can be obtained without making any changes to conventional construction methods.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the experimental equipment used to confirm the effects of the method of the present invention, Figure 2 is an explanatory diagram of the solids obtained with the same experimental equipment, and Figure 3 is an explanatory diagram of the solids obtained in the experiment of the method of the present invention. Figure 4 shows the measurement results of the compressive strength of the solidified body obtained through experiments using the conventional method. A diagram showing the strength measurement results and a diagram showing the strength ratio between the center and the outer periphery of the same measurement results, 5th
Figures (a) to (e) are explanatory diagrams showing examples of construction methods to which the method of the present invention can be applied. Patent applicant Obayashi Co., Ltd. Agent
Person Patent Attorney - Kensuke Shiro
Same as Masatoshi Matsumoto Figure 1 Figure 3 (b) t<4 JL'P-'< 114HA@n14SakiLQ strong "'A,... ($uc: medium ICU strength, 3up: circle mW strength) +
injection! Ji = 20 @ / @ O-a Kai Shin = 204 Shi + - La m = 30z Sea (・ い = 304 Figure 4 (b) 0 - - - 0 Quick entry fbe = 7% Rollo - Be = 10 % Δ−−Δ ・ d=15% ◇−−−〇 ・ Be=20% ☆−−−☆ ・ Ward=304 (C) Figure 5 (b) (d)

Claims (4)

[Claims] (1) A ground improvement method for preparing improved ground by mixing and stirring ground soil and a stabilizing material, characterized in that a mixture of ordinary Portland cement and calcium carbonate is used as the stabilizing material. . (2) The stabilizer according to claim 1, wherein the stabilizer is made of slurry or powder and is added in a volume ratio of 15 to 30% to the ground soil. Strength adjustment ground improvement method. (3) The low strength adjustment ground improvement method according to claim 1 or 2, wherein the stabilizer is directly injected into the improved ground. (4) The low-strength adjustment ground improvement method according to claim 1 or 2, wherein the stabilizer is mixed with the improved ground in advance and then backfilled.