JP2003082348A - System for conditioning weak soil in neutral region into soil capable of giving strength - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve such a problem that there is a fear for an adverse effect on the environment by the soil conditioning technique for recycling because of the alkalinity of the soil thereby conditioned, while requirements for the recycling of an industrial waste comprising e.g. a sludge of high water content or a surplus soil in construction are rapidly increasing nowadays and most of the measures to meet the requirements comprise treatment with a cement-base soil conditioner. SOLUTION: This system comprises mixing under stirring a weak soil with a soil conditioner consisting of two or more of hemihydrate gypsum, magnesium oxide, and a polymeric water absorbent or flocculant. This conditioning allows a weak soil to be granulated and hardened in a neutral region to produce a conditioned soil capable of giving a strength comparable to that of general soil. The conditioned soil can be effectively used similarly as general soil, thus realizing the recycling of a weak soil.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for improving soft soil.

[0002]

2. Description of the Related Art At present, various soft soil treatment technologies such as firing treatment, slurry treatment, highly stable treatment, stabilization treatment, dehydration treatment, advanced dehydration treatment and drying treatment are adopted. In the treatment, a soil improving material having a hardening ability by hydration is widely used.

Gypsum is known to undergo a hardening reaction due to hydration, and is used in medical casts and the like.

Magnesium oxide is known to undergo a hardening reaction by hydration and is used as a concrete material.

Polymeric water-absorbing agents or flocculants, for example, have a natural polymer (guar gum) as a main component and are used as civil admixtures, stabilizers, civil engineering materials such as pouring materials, and the like.

[0006]

At present, a soil improving material containing cement as a main component is widely used for highly stable treatment of soft soil. However, with this type of soil improving material, while sufficient strength can be obtained in the improved soil, the soil becomes alkaline due to the calcium content in the cement, so there is a concern that it may affect plants and animals.

[0007]

By the highly stable treatment of soft soil according to the present invention, almost the same strength development as in the case of performing the same treatment with a conventional cement-based soil improving material is recognized, and at the same time, It is possible to complete the treatment in the sex range.

First, the water in the soil is absorbed by a polymer water absorbing agent or a flocculant. The polymer water-absorbing agent or coagulant absorbs water to solidify (granulate) the soil.

Next, hemihydrate gypsum is hardened by hydration (chemical formula 1) and magnesium oxide (chemical formula 2). (Chemical Formula 1) CaSO ₄・ 1 / 2H ₂ O + 3 / 2H ₂ O → CaSO ₄・ 2H ₂ O (Chemical Formula 2) MgO + (n + 2) H ₂ O → Mg (OH) ₂・ nH ₂ O

Further, the magnesium hydroxide hydrate formed by the hydration reaction of magnesium oxide reacts with phosphoric acid in the soil or carbon dioxide gas in the air to become magnesium phosphate or basic magnesium carbonate, and its strength is increased. Do
(Chemical formula 3). (Chemical formula 3) 5Mg (OH) ₂ · (n-4) H ₂ O + 4CO ₂ → 4MgCO ₃ · Mg (OH) ₂ · nH ₂ O

By a series of operations, the appearance is reformed into particulate soil, and the strength is increased to the same extent as when the conventional cement-based soil improving material is used, for example, to the extent that it is used as a roadbed material.

Further, when the cement-based soil improving material is used, the treated soil exhibits an alkalinity, while the soil improving system of the present invention can perform a series of improvements in the neutral region and the treated soil can be neutralized. Therefore, various advantages such as avoiding the influence of alkaline soil on plants and animals, improving safety during work, and effectively using it as vegetation soil can be obtained.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Here, for the purpose of showing an embodiment of the invention, a strength test and a pH change test conducted in connection with the present invention will be shown.

510 parts by weight of dehydrated cake from a water purification plant having a specific gravity of 1.30 and a water content of 186%, and 50 parts by weight of light-baked magnesia (mainly containing magnesium oxide; hereinafter abbreviated) 50 parts by weight of hemihydrate gypsum A soil conditioner containing 2 parts by weight was mixed and stirred with a pan mixer. As a result, the cone index of the modified soil is 706kN / m ^2, 3D in 1112kN / m ^2, both the 7D and 28D 1200kN / m ² or more intensity obtained in 1D.

340 parts by weight of dehydrated cake from the water purification plant, 50 parts by weight of lightly baked magnesia, 50 parts by weight of hemihydrate gypsum, and polymeric water-absorbing agent 2
A soil conditioner containing 1 part by weight was mixed and stirred with a pan-type mixer. As a result, the cone index of this improved soil is 1.
In all cases of D, 3D, 7D and 28D, a strength of 1200 kN / m ² or more was obtained.

[0016] 510 parts by weight of the water purification plant dehydrated cake, 20 parts by weight of light-baked magnesia, 80 parts by weight of gypsum hemihydrate, water absorbent polymer 2
A soil conditioner containing 1 part by weight was mixed and stirred with a pan-type mixer. As a result, the cone index of this improved soil is 1D
392kN / m ² , 3D 424kN / m ² , 7D 438kN / m ² , 28D 456kN / m ² .
A strength of / m ² was obtained.

510 parts by weight of dehydrated cake from the water purification plant, 30 parts by weight of light-baked magnesia, 70 parts by weight of hemihydrate gypsum, and water absorbent polymer 2
A soil conditioner containing 1 part by weight was mixed and stirred with a pan-type mixer. As a result, the cone index of this improved soil is 1D
460kN in at 529kN / m ^2, 3D at 515kN / m ^2, 7D at 661kN / m ^2, 28D
A strength of / m ² was obtained.

[0018] Hemihydrate gypsum is light burned magnesia for 10 parts by weight
90 parts by weight, 20 parts by weight of hemihydrate gypsum 80
By changing the mixing ratio by 10 parts by weight, such as parts by weight,
Add up to 100 parts by weight in total, and further mix and stir the soil conditioner with 2 parts by weight of the polymeric water-absorbing agent and 510 parts by weight of the water treatment plant dehydrated cake exhibiting pH 6.4,
I examined the change of. The result is shown below. The test results show that in all cases the soil pH is in the neutral range for 28 days.

[0019]

EXAMPLE A highly stable sludge treatment facility for high water content sludge, which has an agitator with a capacity of about 0.5 m ³ and a device for adding high water content sludge and the soil conditioner of the present invention, is prepared.

First, gravel or the like having a size that does not match the capacity of the stirrer is removed in advance, and a certain amount of other high water content sludge is put into the stirrer.

To this, an amount of the present soil improver estimated in advance from the physical properties of the high water content sludge is added, and the mixture is stirred until they are sufficiently mixed. During this time, in the stirrer, 0006-001
The high water content sludge is granulated and hardened by the mechanism shown in 2.
Improve the soil in the neutral range to obtain sufficient strength.

Since this improved soil has a neutral pH, it does not have an adverse effect on the environment and is a valuable material that is not much different from ordinary soil in terms of soil quality, so it can be effectively used for various purposes.

[0023]

[Effects of the Invention] Construction sludge, which is an industrial waste, is generated in large quantities during excavation work and the like, but at present, recycling is carried out only about 10% of this. In addition, it is difficult to secure more landfill sites for landfills due to opposition from residents and nature conservation groups, and it is necessary to establish a recycling system at an early stage.

Under these circumstances, highly stable treatment of highly hydrous sludge is one of the most promising technologies in terms of treatment speed and stability of treated soil, but at the same time, the treated soil becomes alkaline due to its alkaline nature. There is concern about the impact of.

The soft soil improvement system of the present invention can be used in the present age when recycling is required, and can further eliminate the harmful effect of alkali, which is a disadvantage of the highly stable treatment using conventional cement-based soil improving materials. In other words, since the treated soil can be treated like ordinary neutral soil, it can be used for a wide range of purposes and can be widely recycled.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Seiji Miura             Copis 2-10-17 Nakata, Taihaku-ku, Sendai City, Miyagi Prefecture             South Sendai 103 (72) Inventor Naoya Takahashi             4-29-13-203 General Manager Izumi-ku, Sendai City, Miyagi Prefecture F-term (reference) 2D040 AB07 AC05 CA03 CA10 CC05                       CD07                 4H026 CA04 CB03 CB08 CC06

Claims (2)

[Claims] 1. A soil conditioner containing two or more of hemihydrate gypsum, magnesium oxide, a polymeric water-absorbing agent or a flocculant. 2. A soft soil improvement plant equipped with a stirrer and a chemical addition device, wherein the soil improver according to claim 2 is used in an amount of 30 to 250 kg per 1000 kg of soil to mix and stir with the soft soil, and then to a neutral region. A soft soil improvement system for improving soil strength.