JPH0853668A - Method and hardener for treating soft ground by deep mixing - Google Patents

Abstract

PURPOSE:To provide a deep mixing method for treating a soft ground whereby the setting time of an improved soil after mixing a soft soil with a hardener is long. the development of the initial strengths is inhibited, and the long-term strengths of a ground is obtained and to provide a hardener added to a soft soil in the above method by specifying the amts. of alite and belite contained in the hardener. CONSTITUTION:A soft ground is stabilized by a deep mixing method using a cement-base hardener which satisfies the conditions that the binder used contains up to 1wt.% free lime and that 100 pts.wt. soft soil is mixed under stirring with 0-3 pts.wt. alite (3CaO.SiO2), 4-20 pts.wt. belite (2CaO.SiO2), and 0-18 pts.wt. water-granulated blast-furnace slag provided the sum of the amts. of alite, belite, and the slag is 7 pts.wt. or higher.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a hardening material for deep-mixing soft ground.

[0002]

2. Description of the Related Art Along with economic and industrial development, urban development has progressed, resulting in a shortage of land, and the use of soft land, which has not been used, has become increasingly important. Although soft soil is widely distributed in various areas, many soft alluvium is deposited especially on the seabed of each port area. In order to construct a structure on such soft ground, it is necessary to strengthen the soft ground, and various improvement methods have been proposed and attempted.

[0003] In recent years, harbor structures have been gradually increased in size, the depth of improvement of soft ground requiring deep-layer mixing processing has been deepened, and the ground blocks to be improved and integrated have also become larger. For this reason, it has become necessary to take a long time to mix the soft soil and the hardening material.

[0004] In particular, when improving a wide range of soft ground, it is necessary to partially improve it in a wall shape or a cross-girder shape (lattice shape) without making a full improvement in order to improve the efficiency and economy of construction. Has been proposed. In such a case, splicing points will occur, so it is necessary to stir the part of the improved soil layer that has been mixed once, or to mix it across the improved soil layer that intersects vertically and horizontally. There is.

[0005]

However, in the conventional deep mixing process, quick lime, ordinary Portland cement, or blast furnace cement is simply mixed into the soft soil as a hardening material, so that the setting time of the improved soil is reduced. In the mixing process, the improved soil loses its fluidity, causing severe wear and damage to the mixing machine.

[0006] In the case of further jointing, the previously improved mixed soil layer has already started to harden,
This part to be spliced must be excavated with excavation blades. When such a joint is performed, the burden on the mixing machine is large, the mixing efficiency is reduced, and not only the mechanical damage is increased, but also the strength difference between the improved soil and the unimproved soil is large. The penetrating direction is bent, and the unimproved portion is left at the joined portion, thereby causing an unjoined surface, or the adhesion of the joined surface between the already improved soil and the new improved soil is deteriorated, so that the integration of the improved ground is greatly impaired.

As a countermeasure against this, it is conceivable to reduce the amount of the hardening material to be mixed, but in such a case, sufficient strength as the ground cannot be obtained. Although addition of a set retarder is also proposed, its effect is insufficient in soft soil, and a complete set has not been obtained due to the fact that it contains components that are not preferable for environmental protection.

When performing a deep mixing treatment on a soft ground, since a hardening material is mixed with soft soil by stirring, the longer the fluidity of the improved soil after mixing is maintained, that is, the longer the setting time is, the larger the depth is, Preferred for a wide range of treatments. When a normal hardening material is used, the setting time of the improved soil is several hours.
It is desired to be more than time.

[0009] Further, the strength is required to be 20 kgf / cm ² or more in order to secure the necessary supporting force as the ground, and this strength is obtained within three months after the construction due to the setup of construction work. It is hoped that it will be.

According to the present invention, the setting time of the improved soil after the mixing treatment of the soft soil and the hardening material is performed by defining the hardening material to be added in the deep mixing processing of the soft ground by the amount of arit and berit. Is long, the development of initial strength is suppressed,
Moreover, it is an object to provide a deep layer mixing treatment method capable of exhibiting long-term strength as the ground.

[0011]

The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems. As a result, the setting time of the improved soil is sharply shortened when the mixing amount of the arit is increased. In the presence of a small amount of free lime, increasing the blending amount of berit has almost no effect, and the compressive strength at 91 days of age is almost the same value if the combined amount of mixed arit, belit, or slag is equal. This is based on the finding that it can be obtained.

That is, as the first invention, when the cement-based hardening material is mixed with the soft ground to improve the ground, the free lime of the binder used is 1% by weight or less,
And, per 100 parts by weight of the soft soil, arit (3CaO
・ SiO ₂ ) 0-3 parts by weight, Berit (2CaO ・ Si
O ₂ ) 4 to 20 parts by weight, and 0 to 18 parts by weight of granulated blast furnace slag, and added so that the total amount of arit, berit, and granulated blast furnace slag is 7 parts by weight or more, and mixed by stirring. It is a method of deep-mixing soft ground.

As a second invention, based on the above findings,
Free lime is less than 1% by weight, and arit (3CaO ・ Si
O ₂ ) and berit (2CaO · SiO ₂ ) as main components,
3/7 of the amount of arit to the total amount of arit and berit
A hardening material containing the following as a main component of cement is provided.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The soft ground to which the present invention can be applied is composed of alluvial sediment deposited on the seabed or lakes and marshes.
This is different from what is called a sludge layer mainly composed of organic substances that are artificially discharged and deposited.

The components are composed of seawater or freshwater having a water content to solid content in the range of 90 to 150%, as well as gravel, sand, silt, and clay.

In the case of adding arit, if it exceeds 3 parts by weight, the setting of the improved soil is promoted.
A long setting time (end) of 4 hours or more cannot be obtained.
Further, if the total amount of arit, berit and slag or berit alone is added in an amount of less than 7 parts by weight, it is impossible to obtain a compressive strength of 20 kgf / cm ² or more, which is the target strength in the 91-day age. The upper limit of the added amount is not particularly limited from the viewpoint of characteristics, but is naturally determined for economic reasons.

As the slag, a slag having latent hydraulic property is used. In the narrow sense, the latent hydraulic slag referred to here means blast furnace slag slag in the steelmaking industry, but any slag having latent hydraulic properties may be used.

The blast furnace slag slag is quenched into granules (water granulation) by injecting pressurized water into a high-temperature molten state slag generated in the blast furnace.
However, the structure becomes vitreous and is not crystallized, and it does not include arit and berit that are generated when crystallized.

The amount of slag is limited to 90% of berit. Replacing berit with slag in excess of 90% Ca (OH) ₂ released by hydration of berit
And the potential hydraulic property of the slag cannot be sufficiently stimulated.
20 kgf / cm ² or more per day).

The present invention is established only under the condition that the amount of free lime is very small. If the free lime exceeds 1% by weight, it becomes a stimulant of berit and the setting time may be shorter than 24 hours, so that the object of the present invention cannot be achieved. From this, 1% by weight is the limit that does not serve as a stimulant. Further, other cement components such as SO ₃ , Al ₂ O ₃ and Fe ₂ O ₃ are not particularly problematic as long as they are within the range of Portland cement.

When the soft ground is subjected to the deep mixing treatment according to the present invention, the setting time of the improved soil becomes 24 hours or more, the development of the initial strength is suppressed, and the strength at the 91-day age is 20 kgf / cm ² or more. Therefore, there are the following advantages. (1) The working time for mixing the soft soil can be lengthened. (2) Since the improved soil does not congeal or start to harden in the mixing process, the agitator is less worn and damaged, and the working efficiency is good. (3) Since the improved soil layer remains unhardened for a long time at the splicing point, the improved ground at a large depth and a wide area can be integrated. (4) Since the required strength of the ground can be obtained with the 91st timber order, there is no hindrance to the construction process. (5) Since it is not necessary to use a setting retarder in particular, it is easy to adjust the properties of the improved soil, and there is no fear of damaging the environment.

When the present invention is used as a hardening material, free lime is 1% by weight or less and alit (3CaO.Si)
O ₂ ) and berit (2CaO · SiO ₂ ) as main components,
3/7 of the amount of arit to the total amount of arit and berit
The following is the main component of cement, and the blended amount of granulated blast furnace slag is 90% of the amount of berit (2CaO · SiO ₂ ).
Can be replaced with granulated blast furnace slag.

[0023]

EXAMPLES The present invention will be described with reference to experimental examples and examples.

EXPERIMENTAL EXAMPLE Arit was synthesized according to a conventional method by mixing limestone and silica stone so that the molar ratio of CaO and SiO ₂ was 3, and then mixing and pulverizing the mixture in a ball mill into granules. The mixture was fired in a box-type electric furnace at 1500 ° C. for 1 hour to obtain a clinker. The synthesis of berit is limestone, silica stone Ca
O and SiO ₂ are blended so that the molar ratio becomes 2, and B ₂ O ₃ is further added to 1.0, pulverized by a ball mill, pelletized, and baked at 1450 ° C. for 1 hour in a box-type electric furnace to produce a clinker. And

Each of these clinker was crushed by a ball mill to prepare powder having a Blaine value of about 3200 cm ² / g, which was used as an arit and a berit for experiments. These alit and belit were confirmed by X-ray diffraction and microscopic observation.
% Or more was contained.

The free lime of alit and belit was determined by the glycerin alcohol method to be 0.3 and 0.1%, respectively.

The soft soil used was a typical alluvial marine sediment collected from 3 m below the sea floor near the Daikoku Pier in Yokohama Port. The physical properties are shown in Table 1. Clay minerals were confirmed to be montmorillonite, illite, and chlorite by X-ray diffraction, differential thermal analysis and electron microscope observation. It was also confirmed that allophane was present. The experimental sample used was a sieve with a 5 mm net sieve in a naturally hydrated state to remove shells and diatoms.

[0028]

[Table 1]

A setting test was carried out in accordance with JIS R5201 for a mixture of alit and berit alone or in a mixture having a content of 5, 10 and 15 parts by weight per 100 parts by weight of soft soil. A compression strength test was performed according to JIS A1216. Mix arit and berit into soft soil by adding tap water so that the weight ratio of water and the mixture to the arit and berit mixture becomes 0.6, put soft soil into the slurry, and add Hobart. Mixing was performed for 10 minutes with a mixer. Kneading, curing and physical property measurement are all 2
The test was performed in a constant temperature room at 0 ° C.

The setting time (termination) of the obtained improved soil and the compressive strength at 91 days age are shown in FIG. 1 in relation to the admixture amount of arit and berit (added weight part per 100 parts by weight of soft soil). As is clear from the figure, the setting time of the improved soil decreases sharply as the mixing amount of arit increases, while the setting time of the berit hardly affects the setting time. Since the setting time required for the deep mixing process is 24 hours or more, if the equal setting time line that sets the setting time to 24 hours is obtained by the interpolation method, the line shown by the solid line in the figure is obtained.

Therefore, it can be seen that the setting time of the improved soil can be set to 24 hours or more by mixing the arit with 0 to 3 parts by weight with respect to 100 parts by weight of the soft soil. Also, it can be seen that the compressive strength of the 91-day-age is almost the same if the total amount of the mixed arit and berit is equal.

In order to achieve this strength, the clay minerals (eg, allophane) and the amorphous silicate material in the soft soil are formed by the hydration of arit and berit.
(OH) ₂ reacts with calcium aluminosilicate hydrate (2CaO ·
Al ₂ O ₃ · SiO ₂ nH ₂ O) and calcium aluminate hydrate (4CaO · Al ₂ O ₃ · 13H ₂ O, 2CaO ·
Al ₂ O ₃ .8H ₂ O) is generated, and it is judged that the strength development resulting therefrom also contributes synergistically.

Since the strength of the 91-day material age required for the improved ground is set to 20 kgf / cm ² ,
A solid line in FIG. 1 is obtained when the amount of admixture of alit and berit with a compressive strength of / cm ² is obtained by an interpolation method. Therefore, in order to secure the strength of 20 kgf / cm ² or more as the improved soil, it is sufficient that the total amount of arit and berit is 7 parts by weight or more based on 100 parts by weight of the soft soil.

From the above results, when the cement-based hardening material is mixed with the soft ground to perform the ground improvement, the free lime of the binder used is 1% by weight or less, and 100 parts by weight of the soft soil, Alit (3CaO · SiO ₂₎ 0 to 3 parts by weight, Berit (2CaO · SiO ₂₎ 20 parts by weight or less, and Alit, was added as the total amount of Berit (2CaO · SiO ₂₎ is more than 7 parts by weight By stirring and mixing, the setting time and compressive strength necessary for improving soft soil can be obtained.

On the line N in FIG. 1 in which the arit and the berit are mixed in the same proportion as the arit and the berit contained in the ordinary portland cement generally used as the hardening material, even if the mixing amount of the hardening material is changed. The setting time and compressive strength required for the improved soil cannot be satisfied.

Examples 1 to 7, Comparative Examples 1 to 3, Limestone, clay, silica and copper karami having the compositions shown in Table 2 were blended as shown in Table 3 and mixed and pulverized. The raw material was fired in a test rotary kiln according to the experimental example at a firing temperature (1450 ° C. to 1500).
After calcination at ℃) to obtain clinker according to the experimental example, 4% of phosphoric acid by-product gypsum was added to each clinker and crushed with a ball mill to obtain a Blaine value of about 3100 cm ² /
g of cement (cements A, B, C and D)
Each was used as a curing material.

Table 4 shows the chemical analysis values of the obtained cements and the mineral compositions obtained from the Borg equation. The formation of arit and berit was confirmed by X-ray diffraction. The free lime was determined by the glycerin alcohol method according to the experimental examples, and was 0.1 to 0.3%, respectively.

These cements were added to and mixed with the seabed soft soil having physical properties shown in Table 1 collected from the vicinity of the Daikoku Pier in Yokohama Port, and the resulting improved soil was JIS R5201.
According to JIS A1216, a uniaxial compressive strength test was conducted according to JIS A1216.

[0039]

[Table 2]

[0040]

[Table 3]

In addition, the cement is mixed with the soft soil by mixing the cement and seawater (Tokyo Bay) in advance with a cement slurry (seawater / water).
Cement = 0.6) was added to the soft soil, and the mixture was kneaded with a Hobart mixer for 10 minutes. The test specimen for the compressive strength test was molded into a 5φ × 10 cm iron mold, sealed with a polyethylene sheet, and cured in a moist air. Each test was performed in a constant temperature room at 20 ° C.

For comparison, a similar test was conducted using ordinary Portland cement as a hardening material. Table 4 shows the chemical analysis values and mineral composition of this cement. Table 5 shows the results.

[0043]

[Table 4]

[0044]

[Table 5]

As can be seen, according to the present invention, an improved soil having a setting time of at least 24 hours and a strength of 91 days old reaching at least 20 kgf / cm ² can be obtained, while the hardened material of the comparative example can be obtained. Only improved soil of 12 hours was obtained with a long setting time. Further, it can be seen that berit shows an excellent effect even by itself in the presence of a slight amount of free lime.

Examples 8 to 10 and Comparative Examples 4 and 5 Using the respective hardening materials obtained by mixing the cement A used in Example 1 and the ordinary Portland cement used in Comparative Example 1 as shown in Table 6. A softness curing test was performed according to Examples 1-4. Table 6 shows the results.

[0047]

[Table 6]

From the above results, it is possible to prepare a mixture of ordinary Portland cement and cement containing mainly berit so that the contents of arit and berit to soft soil are limited by the present invention, and to perform deep mixing treatment. For example, it was required to obtain an improved soil satisfying both the setting time and the 91-day age strength.

Examples 11 to 16 Cement A used in Example 1, ordinary Portland cement used in Comparative Example 1 and blast furnace water slag (SiO ₂ 3)
4.4%, Al ₂ O ₃ 15.8%, CaO 40.8%)
Were mixed as shown in Table 7 to obtain a cured material. Using each of the hardening materials, a soft soil improvement test was performed according to Example 1. The results are shown in Table 7.

[0050]

[Table 7]

It was confirmed that there was no significant difference in the setting and strength properties of the improved soil even when the slag was replaced by 90% in place of the cement A containing berit as the main constituent. From these results, if the content of alit, berit, and slag is adjusted as in the present invention under the condition that the free lime is 1% by weight or less and the deep layer mixing treatment is performed, both the setting time and the 91-day age strength are satisfied. It was sought to obtain improved soil.

[Brief description of drawings]

FIG. 1 is a diagram showing a 24-hour setting time and a 20 kgf / cm ² intensity line of a tertiary component of soft soil-berrit-allit.

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Claims (3)

[Claims] 1. When mixing cement-based hardening material into soft ground to improve the ground, the binder used has a free lime content of 1% by weight or less, and per 100 parts by weight of the soft soil, Arit (3CaO · SiO ₂ ) 0-3 parts by weight,
Berit (2CaO · SiO ₂ ) 4 to 20 parts by weight or less,
And 0-18 parts by weight of granulated blast furnace slag, and alit,
A method in which berit and granulated blast furnace slag are added so that the total amount is 7 parts by weight or more, and the mixture is stirred and mixed to perform a deep mixing treatment on the soft ground. 2. Free lime is 1 wt% or less, and alit (3CaO.SiO ₂ ), berit (2CaO.Si)
A hardener containing O ₂ ) as a main component and having an arit amount of 3/7 or less relative to the total amount of arit and berit as a main component of cement. 3. The hardened material according to claim 2, wherein 90% or less of the berit amount is replaced by slag.