Soil solidification material, and solidification treatment method of soil

Abstract

To provide a soil solidification material containing gypsum hemihydrate, wherein, when it is added and mixed with soil (unsolidified soil) that is a target of solidification treatment, a mixture of the soil and the soil solidification material can maintain large strength for a long time, and a solidification treatment method.SOLUTION: A soil solidification material containing semi-hydrated gypsum and condensed phosphate salts. Examples of condensed phosphate salts include sodium trimetaphosphate, sodium tetrametaphosphate, sodiumhexametaphosphate, and sodium polyphosphate. An amount of condensed phosphate salts is preferably 0.05 to 10 pts.mass per 100 pts.mass of semi-hydrated gypsum. The soil solidification treatment method includes a solidification material addition step in which the soil solidification material is added to the soil and mixed. The amount of soil solidification material is preferably 10 to 500 kg per cubic meter of soil. The moisture content of the soil is preferably 20% or more.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a soil solidifying material and a method for solidifying soil using the soil solidifying material.

Background Art

[0002] For the excavated soil generated in tunnel excavation work or the like, in order to be used as planting soil or the like, instead of a cement-based solidifying material, for example, a solidifying material containing hemihydrate gypsum as a main component may be used for solidification treatment in a neutral range. When a cement-based solidifying material is used, the excavated soil (solidified treated soil) after solidification tends to be strongly alkaline. As an example of a solidifying material containing hemihydrate gypsum, Patent Document 1, Claim 3 describes a soil solidifying material containing (A) hemihydrate gypsum, (B) a component composed of one or more of light-burned dolomite, quicklime, and slaked lime, and (C) magnesium sulfate anhydride, wherein (A) hemihydrate gypsum is contained in a proportion of 65 to 87% by mass, (B) the component is contained in a proportion of 1 to 30% by mass, and (C) magnesium sulfate anhydride is contained in a proportion of 3 to 30% by mass.

[0003] On the other hand, as a material for plate-like objects such as gypsum boards, in addition to the main components such as gypsum, it is known to use condensed phosphates such as sodium hexametaphosphate for the purpose of improving sag resistance and the like. As an example thereof, for example, Patent Document 2, Claims 1, 30, and Paragraph 0068 describe a continuous method for creating a sound-absorbing panel, including steps such as forming a mixture containing water, a foaming agent, calcined gypsum, and a promoting substance (for example, sodium hexametaphosphate for improving sag resistance).

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] When solidifying soil having a large water content ratio (for example, excavated soil) using a soil solidifying material containing hemihydrate gypsum as a main component, the solidified soil (solidified soil) has a large strength immediately after the addition and mixing of the soil solidifying material, but there is a problem that the strength greatly decreases after a long period (for example, 7 days). An object of the present invention is to provide a soil solidifying material containing hemihydrate gypsum, which can maintain a large strength for a long period (for example, 7 days or more) when added to and mixed with soil (uncured soil) which is an object of solidification treatment, and a method for solidifying soil using the soil solidifying material.

Means for Solving the Problems

[0006] As a result of intensive studies to solve the above problems, the present inventor has found that a soil solidifying material containing hemihydrate gypsum and condensed phosphate can maintain a larger strength even after a long period has passed since the solidification treatment (when adding and mixing the soil solidifying material), as compared with the case of using a soil solidifying material containing only hemihydrate gypsum, and has completed the present invention.

[0007] The present invention provides the following [1] to [6]. [1] A soil solidifying material containing hemihydrate gypsum and condensed phosphate. [2] The soil solidifying material according to [1] above, wherein the condensed phosphate is an alkali metal salt of condensed phosphoric acid. [3] The soil solidifying material according to [2] above, wherein the condensed phosphate is one or more selected from the group consisting of sodium trimetaphosphate, sodium tetrametaphosphate, sodium hexametaphosphate, and sodium polyphosphate. [4] The soil solidifying material according to any one of [1] to [3] above, wherein the amount of the condensed phosphate is 0.05 to 10 parts by mass with respect to 100 parts by mass of the hemihydrate gypsum. [5] The soil solidification material according to any one of [1] to [4] above is added to soil, and 1 m 3 A soil solidification treatment method comprising a solidification material addition step of adding and mixing a solidification material in an amount of 10 to 500 kg per soil. [6] The soil solidification method according to [5] above, wherein the soil has a water content of 20% or more. Effect of the Invention

[0008] The soil solidification material of the present invention contains condensed phosphate in addition to gypsum hemihydrate, and therefore when added to soil and mixed, it can maintain greater strength even after a long period of time (e.g., 7 days or more) has passed since addition and mixing, compared to a soil solidification material containing only gypsum hemihydrate. The soil solidification material of the present invention can be suitably used particularly for soil having a water content of 20% or more. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] The soil solidification material of the present invention contains gypsum hemihydrate and condensed phosphate. Gypsum hemihydrate is a powdered substance with the chemical formula CaSO4·1 / 2H2O (CaSO4·0.5H2O). Unlike cement, gypsum hemihydrate does not raise the pH to a strongly alkaline value after mixing with soil, so it is ideal as a material when using solidified treated soil for planting and other purposes. When used as a soil solidification material, gypsum hemihydrate reacts with the water contained in the soil to become gypsum dihydrate. In the present invention, recycled gypsum hemihydrate produced using waste gypsum board as a raw material may be used as the gypsum hemihydrate.

[0010] Condensed phosphates are salts of the dehydrated condensation product of orthophosphoric acid (H3PO4). In the present invention, as the condensed phosphate, either a cyclic compound or an acyclic (chain) compound can be used. Preferable examples of the condensed phosphate include alkali metal salts of condensed phosphoric acid. Examples of such alkali metal salts include, as salts having a cyclic chemical structure, sodium trimetaphosphate (number of phosphorus atoms: 3), sodium tetrametaphosphate (number of phosphorus atoms: 4), sodium hexametaphosphate (number of phosphorus atoms: 6), etc., and as salts having an acyclic chemical structure, sodium polyphosphate (number of phosphorus atoms: 6), etc. The lower limit of the number of phosphorus atoms contained in the chemical formula of the condensed phosphate is not particularly limited, but from the viewpoint of surely obtaining the effects of the present invention, etc., it is preferably 2 or more, more preferably 3 or more. The upper limit of the number of the phosphorus atoms is not particularly limited, but in consideration of the ease of obtaining commercially available products, etc., for example, it is 20 or less. In the present invention, the amount of the condensed phosphate is preferably 0.05 to 10 parts by mass, more preferably 0.07 to 8 parts by mass, still more preferably 0.1 to 6 parts by mass, still more preferably 0.2 to 1.0 parts by mass, still more preferably 0.3 to 0.7 parts by mass, particularly preferably 0.3 to 0.5 parts by mass with respect to 100 parts by mass of hemihydrate gypsum. When the amount is 0.05 part by mass or more, the effect of maintaining a large strength of the solidified treated soil over a long period can be further enhanced. When the amount is 10 parts by mass or less, in addition to being able to further enhance the effect of maintaining a large strength of the solidified treated soil over a long period, an increase in the material cost of the condensed phosphate can be avoided.

[0011] The soil solidifying material of the present invention can contain materials other than hemihydrate gypsum and condensed phosphate. Examples of other materials include anhydrous gypsum, limestone powder, silica powder, blast furnace slag fine powder, lightly burned magnesia, lightly burned dolomite, quicklime, etc. The amount of other materials is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, particularly preferably 5 parts by mass or less with respect to 100 parts by mass of hemihydrate gypsum. When the amount is 20 parts by mass or less, the effects of the present invention can be obtained more surely and sufficiently. The soil solidifying material of the present invention usually has a powdery form. The soil solidifying material of the present invention is used for the purpose of adding and mixing it into soil such as excavated soil generated in tunnel excavation work to obtain solidified treated soil with enhanced strength for use in planting and the like.

[0012] The method for solidifying soil of the present invention includes a solidifying material addition step of adding and mixing the above-described soil solidifying material into the soil. In the present invention, the lower limit value of the amount of the soil solidifying material, from the viewpoint of further enhancing the effect of maintaining a large strength of the solidified treated soil over a long period, per 1 m of soil 3 is preferably 10 kg or more, more preferably 20 kg or more, still more preferably 30 kg or more, still more preferably 40 kg or more, and particularly preferably 50 kg or more. The upper limit value of this amount, from the viewpoint of avoiding an increase in the material cost of the soil solidifying material, per 1 m of soil 3 is preferably 500 kg or less, more preferably 450 kg or less, still more preferably 400 kg or less, still more preferably 350 kg or less, and particularly preferably 300 kg or less.

[0013] In the present invention, the water content ratio of the soil that is the object of the solidifying treatment is preferably 20% or more, more preferably 22% or more, still more preferably 24% or more, and particularly preferably 26% or more. When this ratio is 20% or more, the above-described effects of the present invention by using condensed phosphate can be obtained more remarkably, which is preferable. In addition, the upper limit of this ratio is not particularly limited, but when the amount of water in the soil is excessive, it is necessary to increase the amount of the soil solidifying material, and the material cost of the soil solidifying material increases. Therefore, it is preferably 150% or less (more preferably 100% or less). The water content ratio of the soil refers to the percentage obtained by dividing the mass of water contained in the soil by the value obtained by subtracting the mass of the water from the mass of the soil (dry mass of the soil) ([mass of water] × 100 ÷ [mass of soil - mass of water]; unit: %).

[0014] The soil solidification treatment method of the present invention can include a solidifying material preparation step of mixing hemihydrate gypsum and condensed phosphate before the solidifying material addition step to prepare the above-mentioned soil solidifying material. In addition, the soil solidification treatment method of the present invention can include a solidified treatment soil storage step of storing the solidified treatment soil after the solidifying material addition step and before the utilization of the solidified treatment soil (for example, input as planting soil to a planting site). In this case, the storage period of the solidified treatment soil is in terms of the age of the material, preferably within 56 days, more preferably within 28 days, and particularly preferably within 14 days. The lower limit of the storage period is not particularly limited, but considering the object of the present invention of maintaining the strength of the solidified treatment soil large over a long period, it is preferably 1 hour or more, more preferably 3 hours or more, still more preferably 6 hours or more, still more preferably 12 hours or more, and particularly preferably 24 hours or more. Examples of the storage method include storage indoors and storage covered with a sheet outdoors.

Examples

[0015] Hereinafter, the present invention will be specifically described by way of examples, but the present invention is not limited to these examples. [Materials] The following materials were used. (a) No. 5 silica sand (dry soil, a material for simulated soil) (b) Tap water (water, a material for simulated soil) (c) Hemihydrate gypsum (powder form; manufactured by Fuji Machine Co., Ltd.) (d) Sodium trimetaphosphate (powder form; manufactured by Sigma-Aldrich; CAS number: 7785-84-4) (e) Sodium hexametaphosphate (powder form; manufactured by Fujifilm Wako Pure Chemical Corporation; CAS number: 10124-56-8) (f) Sodium polyphosphate (powder form; manufactured by Fujifilm Wako Pure Chemical Corporation; CAS number: 68915-31-1)

[0016] [Example 1] 100 parts by mass of hemihydrate gypsum and 0.1 part by mass of sodium trimetaphosphate were mixed to obtain a soil solidifying material. On one hand, 2,000 g of No. 5 silica sand and 540 g of tap water were mixed at a low speed (140 rpm) for 1 minute and 30 seconds using a tabletop mixer to obtain simulated soil (water content ratio: 27%; untreated soil). Next, the simulated soil and 300 kg of soil solidifying agent per 1 m 3 of the simulated soil were mixed at a low speed (140 rpm) for 1 minute and 30 seconds using a tabletop mixer to obtain solidified soil. Immediately after the preparation (mixing) of the solidified soil (material age: 0 days), the cone index of the solidified soil was calculated using "JIS A 1228:2020" (Test method for cone index of compacted soil). On the other hand, the prepared solidified soil was sealed in a synthetic resin bag, taken out at a material age of 7 days, and the cone index was calculated in the same manner as the above method.

[0017] [Examples 2 - 8] As shown in Table 1, experiments were conducted in the same manner as in Example 1 except that the type and amount of condensed phosphate were changed. [Comparative Example 1] Experiments were conducted in the same manner as in Example 1 except that untreated soil was used instead of solidified soil. [Comparative Example 2] Experiments were conducted in the same manner as in Example 1 except that a soil solidifying agent consisting only of hemihydrate gypsum was used instead of the soil solidifying agent in Example 1. The above results are shown in Table 1. In Table 1, "parts" represents parts by mass. "Penetration impossible" means that measurement is impossible (the cone index exceeds 1,500 kN / m 2 ). In Comparative Example 1, since the value of the cone index at a material age of 0 days was very small, the experiment to obtain the cone index at a material age of 7 days was not conducted.

[0018]

Table 1

[0019] From Table 1, it can be seen that in Examples 1 to 8, the cone index at 7 days of material age is larger than that in Comparative Example 2. In particular, when comparing among Examples 1 to 6 (all using sodium trimetaphosphate), in Examples 2 to 3, the cone index at 7 days of material age is "unpenetrable" (the cone index is so large that it cannot be measured), indicating that better results are obtained compared to Examples 1, 4 to 6. Also, Examples 7 to 8 are experimental examples using condensed phosphates other than sodium trimetaphosphate. Since the amount of the condensed phosphate is 0.5 parts by mass, similar to Examples 2 to 3 (amount of condensed phosphate: 0.3 to 0.5 parts by mass), the cone index at 7 days of material age is "unpenetrable", showing that better results are obtained compared to Examples 1, 4 to 6.

Claims

**Claim 1** A soil solidifying material containing hemihydrate gypsum and condensed phosphate. **Claim 2** The soil solidifying material according to Claim 1, wherein the condensed phosphate is an alkali metal salt of condensed phosphoric acid. **Claim 3** The soil solidifying material according to Claim 2, wherein the condensed phosphate consists of one or more selected from the group consisting of sodium trimetaphosphate, sodium tetrametaphosphate, sodium hexametaphosphate, and sodium polyphosphate. **Claim 4** The soil solidifying material according to Claim 1, wherein the amount of the condensed phosphate is 0.05 to 10 parts by mass with respect to 100 parts by mass of the hemihydrate gypsum. **Claim 5** A method for solidifying soil, comprising a solidifying agent addition step of adding and mixing the soil solidifying agent according to any one of claims 1 to 4 to the soil in an amount of 10 to 500 kg per 1 m of the soil. ３ ​ **Claim 6** The method for solidifying soil according to Claim 5, wherein the soil has a water content ratio of 20% or more.

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