JP2009185159A - Soil-improving material and soil-improving method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a soil-improving material which can improve a ground strength and a bearing power by adding to a soft soil, suppress a rise of soil pH due to the addition and prevent an adverse effect to an ecosystem caused by a strong alkaline soil, and to provide a soil-improving method using the same. <P>SOLUTION: The soil-improving material produced by compounding 50-100 pts.mass activated clay and 50 pts.mass or less hemihydrate gypsum to 100 pts.mass unslaked lime and/or light burnt dolomite is added in an amount of 200 kg or less to 1 m<SP>3</SP>soft soil, and blended. Thereby, the soil is solidified, the ground strength and the bearing power are improved, and the pH is suppressed low. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

The present invention relates to a soil quality improving material and a soil quality improving method using the same. Specifically, it is added to soft soil to solidify the soil to increase its strength, and suppress the increase in soil pH accompanying addition, causing the soil to become strongly alkaline, The present invention relates to a soil improvement material that prevents adverse effects and a method for improving the soil quality using the same.

In Japan, soft soils including volcanic ash clay are widely distributed. In particular, the ground required for social activities, such as the plains where many roads, houses and public buildings are installed, is composed of soft soil containing a large amount of moisture and organic matter. For the purpose of strengthening the ground of such soft soil to increase bearing capacity and to facilitate the movement and activities of construction machinery, it is often the case that soil improvement materials are added to the soil. .

Soil improvers used for this purpose are generally quick lime, light calcined dolomite or cement based soil conditioners. Its action is to absorb a large amount of water in the soil and lower the plasticity index, thereby increasing the strength of the ground and obtaining bearing capacity. Depending on the type of soil improvement material, it may work to further improve the above ground strength and bearing capacity by causing an ion exchange reaction, pozzolanic hardening reaction, or carbonation reaction in the soil. There is what is called “soil-solidifying material”. However, soil quality improving materials, including such soil-solidifying materials, generally tend to increase the pH of the soil, and sometimes the pH rises to near 12. When the pH of the soil becomes high, there is a concern that rainwater will cause strong alkaline water to flow out and adversely affect animals and plants and the ecosystems that contain them.

In recent years, with the intention of solidifying the soil to avoid increasing the pH of the soil, not only quicklime and light calcined dolomite but also dihydrate gypsum, hemihydrate gypsum, anhydrous gypsum, magnesium oxide, slag slag, fly ash A soil-solidifying material that has been made weakly alkaline by blending and the like is being developed. It is difficult to lower the pH of the soil simply by adding gypsum, magnesium oxide, etc. to quick lime or lightly burnt dolomite, so try to reduce the amount of quick lime, calcium phosphate, aluminum hydroxide, etc. It has been. Furthermore, a trial production of a weakly alkaline soil-solidifying material mainly composed of gypsum and magnesium oxide without using quick lime has been reported.

To give concrete examples recently proposed, first, 20 to 70 parts by weight of gypsum-based building waste and 30 to 80 parts by weight of quicklime are blended, and 0.4 to 1.2 of the theoretical water amount required for quicklime hydration. There is a soil treatment material composition in which double water is added and mixed (Patent Document 1). This composition is intended for effective use of waste materials, but has a high proportion of gypsum to quick lime.

Next, there is a low alkaline solidifying material composition obtained by blending magnesium oxide and aluminum hydroxide in a weight ratio of 10:90 to 80:20. With respect to 100 parts by weight, dihydrate gypsum, hemihydrate gypsum, There has also been proposed a composition in which one or more selected from anhydrous gypsum, aluminum sulfate, and iron sulfate are added at a ratio of 100 parts by weight or less (Patent Document 2). Magnesium oxide is effective in lowering the pH of the soil because its pH after hydration is low compared to that of quicklime, but the hydration reaction of magnesium oxide is less than that of quicklime, so it is reactive In order to increase the particle size, it is necessary to use finer particles (average particle size of 15 μm). Even in that case, since the pH of the soil may be increased with magnesium oxide alone, it is necessary to add aluminum hydroxide and gypsum to further ensure the effect of lowering the pH.

A soil solidifying material mainly composed of magnesium oxide having fine particles (particle diameter of 1 to 15 μm) has also been disclosed (Patent Document 3). This soil solidifying material is composed of 20 to 60% by mass of magnesium oxide, 1 to 50% by mass of magnesium sulfate, calcium and / or aluminum sulfate, and 10 to 60% by mass of calcium carbonate. On the other hand, the addition of quick lime and / or lightly burned dolomite at a ratio of 1 to 90 parts by mass has also been proposed.

Furthermore, there is a soil-solidifying material that uses magnesium oxide that is finer (average particle size is 1 to 5 μm, and that exceeds 10 μm is 10% by volume or less) and has an apparent density of 0.3 to 0.8 g / cm ³ ( Patent Document 4). This also has the composition which mix | blended said sulfate 1-50 mass% and calcium carbonate 10-60 mass% with magnesium oxide. A soil-solidifying material composed mainly of magnesium oxide is effective in increasing the strength of the ground and suppressing the increase in pH. However, the finer the particles, the more difficult it is to manufacture and handle. It is a disadvantage that the property becomes high.
JP 2003-183653 A JP2005-306939 JP2007-161838 JP2007-161839

The object of the present invention is to use quick lime and / or lightly burned dolomite as the main material, add hemihydrate gypsum if necessary, and add it to the soil to increase its ground strength and supporting capacity, and the soil pH accompanying the addition It is an object of the present invention to provide a soil quality improving material that can suppress the rise of soil and prevent the adverse effects on the ecosystem caused by the soil becoming strongly alkaline.

The basic aspect of the soil improvement material of the present invention is that 50 to 100 parts by mass of activated white clay is blended with 100 parts by mass of quicklime or lightly burned dolomite, and when added to the soil, the soil is solidified, It is a soil improvement material that can suppress an increase in pH.

A preferred modification of the soil improvement material of the present invention is that 50 to 100 parts by mass of activated clay and 50 parts by mass or less of hemihydrate gypsum are blended with 100 parts by mass of quicklime or light-burned dolomite, and added to the soil. It is a soil quality improving material that can solidify the soil and suppress an increase in its pH.

The soil quality improvement method of the present invention is performed by adding the soil improvement material of the above basic aspect or a preferable modified aspect to soft soil, usually in an amount of 200 kg or less with respect to 1 m ^{3 of} soil. It is a soil quality improvement method comprising solidifying soil to increase its ground strength and supporting force and suppressing an increase in pH.

The mechanism by which quick pH and lightly burned dolomite are added to the soil increases the pH. CaO and MgO react with the water in the soil to produce hydroxide, which dissolves in the water and calcium ions (metal cations) ( The purpose is to generate Ca ²⁺ ) and magnesium ions (Mg ²⁺ ) and hydroxy ions (OH ⁻ ) which are anions. Therefore, in the soil improvement material of the present invention, an increase in pH is suppressed by blending activated lime and / or lightly baked dolomite that can be exchanged with these metal cations to give hydrogen ions (H ⁺ ). Succeeded.

Thus, the soil improvement material of this invention can suppress the raise of the pH of soil, implement | achieving the increase in the ground strength and supporting force by quick lime and / or light-burning dolomite. Since extremely fine particles are not used, there is no problem in manufacturing and handling. Since activated clay is obtained at a relatively low cost, the production cost does not increase.

According to a preferred modification of the soil improvement material of the present invention, the addition of hemihydrate gypsum increases the ability to solidify the soil, and the gypsum is neutral and has the effect of mitigating the increase in pH. The effect intended by the invention can be further enhanced. This hemihydrate gypsum can be prepared by processing building waste materials and can be used advantageously for the treatment of waste.

Activated clay is a strongly acidic clay made by treating bentonite, a clay mineral having cation exchange properties, with sulfuric acid and changing the exchangeable cations to hydrogen ions. It is the role of the activated clay that H ^{+ in the} activated clay is exchanged with Ca ²⁺ and Mg ²⁺ present in the soil, neutralizing OH ⁻ in the soil and lowering the pH. In this way, even when quicklime or lightly burnt dolomite is added to the soil, the effect of lowering the pH of the soil is more harmful than the addition of gypsum or the addition of magnesium oxide. Can be better prevented.

As described above, the mixing ratio of the activated clay to quicklime and / or lightly burnt dolomite is 50 to 100 parts by mass of the latter with respect to 100 parts by mass of the former. If the amount is less than 50 parts by mass, the effect of lowering the pH is insufficient. On the other hand, if the amount exceeds 100 parts by mass, the effect of increasing the ground strength and bearing capacity will be insufficient. Choose the amount of addition.

In a preferred modification in which hemihydrate gypsum is added, as described above, 50 wt. The following parts are blended. In this case as well, if the amount of hemihydrate gypsum is increased, the amount of quicklime or light calcined dolomite is relatively reduced, so the effect of increasing the ground strength and bearing capacity is discounted. The effect is not so great because gypsum compensates for it to some extent by the solidification of its own hydration. However, the amount added should be within 50 parts by mass.

When soil solidification and pH suppression are performed using the soil improvement material of the present invention, an amount of 200 kg or less of the soil improvement material is added per 1 m ^{3 of} soft soil, and the mixture is sufficiently mixed and reacted. Thereby, the soil is solidified, and the ground strength and supporting force are increased, and the increase in pH is suppressed. The appropriate amount of soil amendment depends on the nature of the soil to be improved and the degree of target improvement, that is, the ground strength and bearing capacity to be achieved. If a specific construction example is given, the following numerical value (uniaxial compressive strength in an indoor addition test) is required.
Improvement work for the foundation ground of high-rise buildings: 1570kN / m ²
Road ground reinforcement work for motorway construction: 600kN / m ²
Sewerage pipe foundation ground improvement work: 68kN / m ²

If necessary to obtain the target uniaxial compressive strength as described above, the amount of quicklime or light-burned dolomite must be increased. However, when the amount to be added exceeds 200 kg per 1 m ^{3 of} soil, a cement-based solidifying material capable of giving high uniaxial compressive strength in a smaller amount is generally used. The reason for this is that adding a large amount is disadvantageous in terms of both the cost of the soil quality improving material itself and the cost of adding to and mixing with the soil, and the use of expensive cement-based solidifying material is justified. .

[Soil improvement material]
A soil improvement material was manufactured using the following materials.
・ Quicklime and light-burned dolomite: Crushed baked limestone or light-burned dolomite and used 3mm all-use product. ・ Activated white clay: Made by Nippon Active Shirato Co., Ltd. For comparison with the one prepared by pulverizing and treating the waste gypsum board, one having a composition outside the scope of the present invention was also prepared. The blending ratios (mass%) of these Examples and Comparative Examples are as shown in Table 1.

Table 1

[Target soil]
As the objects to be improved, five kinds of soils having the characteristics described in Table 2 below were selected.
Table 2

[Test method]
The sample soil to which the soil conditioner is added is packed in a cylindrical mold having an inner diameter of 50 mm and a height of 100 mm, and using a 1.5 kg rammer, the first layer 10 times, the second layer 25 times, the third layer 25 times, 4 A cylindrical specimen is made with 40 times of compaction. Each specimen was cured in air at 23 ° C. for 7 days, and then the soil improvement effect was evaluated by measuring the uniaxial compressive strength according to JIS A1216 and the pH of the soil suspension according to JGS0211.

[Comparative Examples 1-6]
For Kanto Loam A, soil improvement material No. 1 and 2 (quick lime or lightly burned dolomite alone) were added to try to improve the soil quality. The amount added is 50 kg, 100 kg or 150 kg per 1 m ^{3 of} soil. The test results are shown in Table 3 together with the amount of soil improvement material added. The data in Table 3 are shown in the graph of FIG. 1 for the uniaxial compressive strength and the graph of FIG. 2 for the pH of the soil suspension.

Table 3

In Comparative Examples 1 to 6, the uniaxial compressive strength increases as the amount added increases both when quick lime is added and when lightly burned dolomite is added, but the pH also increases accordingly. The reason is that as the amount of quicklime or lightly burned dolomite increases, the amount of hydroxy ions produced increases. When the soil improvement agent 100 kg / m ³ is added, to obtain a high uniaxial compressive strength in excess of 200 kN / m ^2, in the case of adding dolomitic 150 kg / m ^3, the very high strength realized in excess of 400 kN / m ² In all cases, however, the pH was approximately 12.

[Comparative Examples 7 to 10]
Again for Kanto Loam A, the soil improvement material No. 3 and 4 (quick lime or light calcined dolomite plus hemihydrate gypsum) were added to try to improve the soil quality. The amount added is 100 kg or 150 kg per 1 m ^{3 of} soil. The test results are shown in Table 4 together with the amount of soil improvement material added. The data of Table 4 is shown in the graph of FIG. 3 for the uniaxial compressive strength, and the graph of FIG. 4 for the pH of the soil suspension.

Table 4

In Comparative Examples 7-10, compared with Comparative Examples 1-6, the uniaxial compressive strength when the addition amount of the soil conditioner is the same is somewhat lower, but the pH is also reduced to approximately 11.

[Examples 1 to 5]
For Kanto Loam A, soil improvement material No. 1 to 5 (active lime added to quick lime or light calcined dolomite) was added to try to improve the soil quality. The amount added is 100 kg or 150 kg per 1 m ^{3 of} soil. The test results are shown in Table 5 together with the addition amount of the soil conditioner.

Table 5

In Examples 1 to 3, the uniaxial compressive strength decreases as the ratio of the activated clay to the light-burned dolomite constituting the soil improvement material increases, but the pH of the soil suspension decreases. In Example 3 to which a large amount of activated clay was added, the uniaxial compressive strength was low, but the pH was remarkably low. In Examples 4 and 5 in which the amount of the soil conditioner added is high, the uniaxial compressive strength is improved and the increase in pH is suppressed.

From the data in Table 5, the size of the ratio of [quick lime and / or light burned dolomite] to the whole soil improvement material, that is, [quick lime and / or light burned dolomite + activated white clay], uniaxial compressive strength and soil suspension Was plotted with respect to pH, and the graphs of FIGS. 5 and 6 were obtained. From the graph of FIG. 5, it can be seen that the higher the ratio of [quick lime and / or light burned dolomite] to the activated clay, the higher the uniaxial compressive strength. From the graph of FIG. 6, it can be seen that the pH cannot be lowered if the ratio of the activated clay is low.

[Examples 6 to 10]
For Kanto Loam A, soil improvement material No. 5 or No. 6 (active lime or light dolomite plus activated clay and hemihydrate gypsum) was added to try to improve the soil quality. The amount added is 100 kg or 150 kg per 1 m ^{3 of} soil. The test results are shown in Table 6 together with the amount of the soil improvement material added. The data in Table 6 is shown in the graph of FIG. 7 for the uniaxial compressive strength and the graph of FIG. 8 for the pH of the soil suspension.

Table 6

In Examples 6-9, pH has reached 10 or less. This is the effect of adding hemihydrate gypsum. Particularly in Example 9, the uniaxial compressive strength equivalent to that of Comparative Example 3 to which only quicklime was added was obtained, and the pH was successfully reduced from 12.3 to 10.6.

[Comparative Examples 11 to 18] [Examples 10 to 17]
In order to confirm the difference depending on the soil to be subjected to soil improvement, Comparative Example No. 3 (light calcined dolomite plus hemihydrate gypsum) or Comparative Example No. The soil improvement material of 4 (what added hemihydrate gypsum to quick lime) was used. In addition, Example No. 5 (light dolomite added with activated clay and hemihydrate gypsum) or Example No. Soil quality improver 6 (active lime added with activated clay and hemihydrate gypsum) was used. The amount added is 100 kg / m ³ in all cases. The results are shown in Comparative Example No. 11 to 18 are shown in Table 7, and Examples 10 to 17 are shown in Table 8.

Table 7

Table 8

In both Comparative Examples and Examples, higher uniaxial compressive strength was obtained than in the case of Kanto Loam A, but the pH was relatively high. However, the example was able to suppress the increase in pH more than the comparative example. This is the effect of adding activated clay and hemihydrate gypsum to quicklime and / or light burned dolomite according to a preferred embodiment of the present invention.

Below, a construction example on site and the above-described embodiment will be described in comparison. The uniaxial compressive strength required in various sites is as follows.
1) Temporary road for crawler crane (Tochigi Prefecture): 86kN / m ²
2) Renovation of retaining wall foundation (Ibaraki Prefecture): 140kN / m ²
3) Steep banking construction: 167 kN / m ²
4) Temporary road construction (Fukuoka): 245kN / m ²
Examples 2, 4, 6-9 and 14 listed above exceed the target strength of construction example 1), Examples 7-9 exceed the target strength of construction examples 1) -3), and Example 9 is a construction example. Since it exceeds the target strength of 4), it can be applied to the actual construction. It goes without saying that the load on the environment is reduced because the pH of the soil is kept low as compared with the case of using the quick-lime or light-burned dolomite alone, in addition to the improvement in strength.

It is data of the comparative example of this invention, Comprising: The graph which shows the relationship between the uniaxial compressive strength of the test body of Comparative Examples 1-6, and the addition amount of a soil improvement material. It is data of the comparative example of this invention, Comprising: The graph which shows the relationship between pH of the soil suspension of the test body of Comparative Examples 1-6, and the addition amount of a soil improvement material. It is data of the comparative example of this invention, Comprising: The graph which shows the relationship between the uniaxial compressive strength of the specimen of comparative examples 7-10, and the addition amount of a soil improvement material. It is data of the comparative example of this invention, Comprising: The graph which shows the relationship between pH of the soil suspension of the test body of Comparative Examples 7-10, and the addition amount of a soil improvement material. It is data of the Example of this invention, Comprising: The graph which shows the influence of the composition of a soil improvement material given to the uniaxial compressive strength of the test body of Examples 1-5. It is data of the Example of this invention, Comprising: The graph which shows the influence of the composition of a soil improvement material which gives to the pH of the soil suspension of the test body of Examples 1-5. It is data of the Example of this invention, Comprising: The graph which shows the relationship between the uniaxial compressive strength of the specimen of Examples 6-9, and the addition amount of a soil improvement material. It is data of the Example of this invention, Comprising: The graph which shows the relationship between pH of the soil suspension of the test body of Examples 6-9, and the addition amount of a soil improvement material.

Claims (4)

A soil improvement material comprising 50 to 100 parts by weight of activated clay with respect to 100 parts by weight of quicklime or lightly burnt dolomite, and when added to the soil, solidifies the soil and suppresses an increase in pH. 50 to 100 parts by weight of active clay and 50 parts by weight or less of hemihydrate gypsum are blended with 100 parts by weight of quicklime or lightly burned dolomite, and when added to the soil, the soil is solidified and its pH is increased. Soil improvement material that can be suppressed. By adding an amount of 200 kg or less per 1 m ³ of soil quality improving material according to claim 1 or 2 to soft soil, the soil is solidified to increase its ground strength and supporting capacity, and the pH of the soil is improved. A soil quality improvement method consisting of suppressing the rise. The soil quality improving method according to claim 3, wherein the soft soil is a soil of the Kanto Loam layer.

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