Method for solidifying soil-based material

Abstract

To provide a method for effectively solidifying a soil-based material.SOLUTION: A method for solidifying a soil-based material includes: a solidifying agent preparation step for preparing a solidifying agent containing casein, calcium ions, carbonate ions, urea, and urease; and a soil-based material solidification step for contacting the solidifying agent with the soil-based material to solidify the soil-based material.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a method for solidifying soil material such as sand, a method for producing a solidified soil material, and a soil material solidifying agent for solidifying soil material. [Background technology]

[0002] In recent years, in coastal development, CSG (Cemented Sand and Gravel) that was built as a seawall has been covered with embankments and sand to create slopes, with consideration given to the landscape of the sand dunes and the protection of precious flora and fauna. However, if the slopes of these seawalls are left as they are, the embankments and sand will be eroded by wind and other factors, and blown sand will be generated, which will have an impact on the surrounding residential environment. In addition, erosion of the beach cliffs formed by the erosion of coastal sand dunes and beaches by waves and other factors is progressing, raising concerns about the retreat of the coastline. To solve these problems, methods of improving soil quality and solidifying soil materials have been proposed.

[0003] As such a method, for example, a soil improvement method has been proposed in which a first solution, which is an aqueous solution of urease, and a second solution, which is an aqueous solution of urea and a calcium salt, are each injected into the ground, or the first solution and the second solution are mixed and then injected into the ground immediately (see Patent Document 1). However, this method is not necessarily satisfactory in terms of solidification strength, etc. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5599032 Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a method for effectively solidifying soil material. [Means for solving the problem]

[0006] As a result of intensive research into solving the above-mentioned problems, the inventors discovered that when a solution containing micelles of casein and calcium ions is mixed with soil material, the calcium ions in the micelles react with carbonate ions, causing calcium carbonate to precipitate in a manner that connects the soil material, thereby firmly solidifying the soil material, and thus completed the present invention.

[0007] That is, the present invention is as follows. [1] A method for solidifying soil material, comprising: a solidifying agent preparation step of preparing a solidifying agent containing casein, calcium ions, carbonate ions, urea, and urease; and a soil material solidification step of contacting the solidifying agent with the soil material to solidify the soil material. [2] A method for producing a solidified soil material, comprising: a solidification agent preparation step of preparing a solidification agent containing casein, calcium ions, carbonate ions, urea, and urease; and a soil material solidification step of contacting the solidification agent with a soil material to solidify the soil material.

[0008] [3] The method according to [1] or [2] above, wherein the casein and calcium ions of the solidifying agent form micelles. [4] The method according to any one of [1] to [3] above, wherein the solidifying agent preparation step comprises mixing a solution A containing casein, carbonate ions, and urease, a solution B containing urea, and a solution C containing a calcium salt to prepare the solidifying agent. [5] The method according to [4] above, wherein solution A contains a culture medium of a urease-producing bacterium cultured in a medium containing casein and urea. [6] The method according to [4] or [5] above, wherein the calcium salt in solution C is calcium chloride, calcium acetate or calcium nitrate.

[0009] [7] The method according to any one of [1] to [6] above, characterized in that the soil material solidification step comprises a soil material slurry preparation step of mixing the solidifying agent with soil material to prepare a soil material slurry, and a soil material slurry injection step of injecting the soil material slurry into a predetermined location. [8] The method according to any one of [1] to [6], characterized in that the soil material solidification process includes a solidification agent injection process of injecting the solidification agent into the ground. [9] The method according to any one of the above [1] to [8], wherein in the soil material solidification step, the solidification agent forms vaterite crystals of calcium carbonate to solidify the soil material.

[0010]

[10] A soil material solidification agent comprising casein, calcium ions, carbonate ions, urea, and urease.

[11] The soil solidification agent according to

[10] above, characterized in that the casein and calcium ions form micelles.

[12] The soil material solidification agent according to

[10] or

[11] above, comprising: solution A containing casein, carbonate ions and urease; solution B containing urea; and solution C containing a calcium salt.

[13] The soil solidification agent according to

[12] above, wherein solution A contains a culture medium of a urease-producing bacterium cultured in a medium containing casein and urea.

[14] The soil solidification agent for soil material according to

[12] or

[13] above, characterized in that the calcium salt of solution C is calcium chloride, calcium acetate or calcium nitrate. Effect of the Invention

[0011] According to the method of the present invention, soil material can be effectively solidified. [Brief description of the drawings]

[0012] [Figure 1]FIG. 1 shows the relationship between axial stress and axial strain, and the relationship between volumetric strain and axial strain in the “Soil Consolidation-Drainage (CD) Triaxial Compression Test (Geotechnical Society Standard JGS 0524-2009)” of the test specimens, where (a) is the solidified test specimen of Example 1, and (b) is the untreated test specimen of the comparative example. [Diagram 2] FIG. 1 shows the deformation of the specimens immediately after the CD test was terminated, where (a) is the solidified specimen of Example 1 (effective confining pressure 100 kPa) and (b) is the untreated specimen of the comparative example (effective confining pressure 50 kPa). [Diagram 3] The upper figure is an SEM image of a sand particle of the solidified specimen of Example 1. The middle figure is an enlarged SEM image of the sand particle, and the lower figure is a diagram showing element mapping (calcium, silicon) by EDX. [Figure 4] 1 shows X-ray diffraction patterns of crystals precipitated in a test specimen, with the upper diagram showing the crystalline substance precipitated by adding casein peptone and using urease-positive bacteria (Example 1), the middle diagram showing the crystalline substance precipitated by adding casein peptone and using a urease enzyme reagent (Example 2), and the lower diagram showing the crystalline substance precipitated by using a urease enzyme reagent without adding casein peptone (Comparative Example). [Diagram 5] FIG. 1 shows the results of crystal observation using a digital microscope of a solidified specimen of Example 1 in which casein peptone was added and urease-positive bacteria were used. [Figure 6] FIG. 13 shows the results of crystal observation using a digital microscope of a test specimen as a comparative example in which a urease enzyme reagent was used without the addition of casein peptone. [Figure 7] FIG. 1 is a diagram showing the relationship between the mean effective stress and the principal stress difference 1 / 2 at the maximum axial difference stress for the solidified specimen of Example 1 and the untreated specimen of the comparative example. [Figure 8] FIG. 1 shows the relationship between the principal stress difference and axial strain in a CD test (effective confining pressure 50 kPa) of the solidified specimen (dune sand) in Example 1, and the relationship between the volumetric strain and axial strain (comparison based on initial relative density). [Figure 9]Photographs of solidified specimens in the examples. The left photograph is a photograph of a solidified specimen solidified using urease (Example 2), and the right photograph is a photograph of a solidified specimen solidified using urease-producing bacteria (Example 1). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] [Method for solidifying soil material and method for manufacturing solidified soil material] The method for solidifying soil material and the method for producing solidified soil material of the present invention are characterized by comprising a solidifying agent preparation step of preparing a solidifying agent containing casein, calcium ions, carbonate ions, urea, and urease, and a soil material solidification step of contacting the solidifying agent with the soil material to solidify the soil material.

[0014] Here, the soil material to be solidified in the method of the present invention is a soil material in the engineering classification system of soil materials, and is preferably sandy soil (major classification). The method of solidifying soil material of the present invention can effectively solidify even sandy soil, which is difficult to solidify.

[0015] The casein of the present invention includes casein peptone in addition to casein as a protein.

[0016] In addition, the calcium ions of the present invention can be present in the solidifying agent by adding a calcium salt. Examples of calcium salts include calcium chloride, calcium acetate, and calcium nitrate. It is preferable to use calcium chloride from the standpoint of adjusting the pH of the solution, etc.

[0017] Carbonate ions are produced by the decomposition reaction of urea by urease, as shown in the following formula. (NH2)2CO+2H2O(+Urease) → 2NH3+H2CO3 NH3+H2O ← →NH4 + +OH - H2CO3← → HCO3 - +H + ← →CO3 2- +2H+

[0018] The urease of the present invention also includes urease-producing bacteria that produce urease. When using urease-producing bacteria, it is preferable to use urease-producing bacteria obtained from the soil material to be solidified (the soil material at the site to be solidified). This makes it possible to more effectively solidify the soil material.

[0019] In the following, the casein, calcium ions, carbonate ions, urea, and urease contained in the solidifying agent may be referred to as essential components of the solidifying agent.

[0020] The method for solidifying soil material and the method for producing solidified soil material of the present invention include a method in which a solidifying agent containing all essential components is prepared in advance, and then the solidifying agent is brought into contact with the soil material to solidify the soil material (pre-mixing method), as well as a method in which solutions containing one or more essential components of the solidifying agent are added sequentially to the soil material so that all essential components are mixed in the presence of the soil material, that is, a method in which the solidifying agent preparation step and the soil material solidification step are carried out simultaneously (in-soil material mixing method). In the present invention, the former pre-mixing method is preferred because it can solidify the soil material more effectively.

[0021] Specifically, the pre-blending method includes a solidification agent preparation step of preparing a solidification agent containing casein, calcium ions, carbonate ions, urea, and urease, and a soil material solidification step of contacting the solidification agent obtained in the solidification agent preparation step with a soil material to solidify the soil material. In the solidification agent, micelles of casein and calcium ions are formed, and the formation of these micelles is an important point of the present invention. In addition, the pH of the solidification agent is preferably 8 to 11, more preferably 8.5 to 10.5, and even more preferably 9.0 to 10.0, from the viewpoint of promoting the production of calcium carbonate. In addition, after the preparation of the solidification agent, it is preferable to contact the soil material within 1 hour, more preferably within 30 minutes, and even more preferably within 10 minutes.

[0022] On the other hand, in the case of the in-soil material blending method, for example, a solution containing casein and calcium ions may be added to the soil material, and a solution containing urea and a solution containing urease may be added sequentially or simultaneously in any order. The order in which these solutions are added and the pre-blending of the solutions (for example, a solution containing urea and urease) may be appropriately determined, but as described above, the important point of the present invention is that a solution containing casein and calcium ions is used in the method of the present invention, and micelles of casein and calcium ions are formed.

[0023] In the present invention, it is preferable to use solution A containing casein, carbonate ions and urease as one of the solidifying agent preparation solutions, and specifically, it is particularly preferable to use solution A containing a culture solution of a urease-producing bacterium cultured in a medium containing casein and urea. This solution A contains casein, carbonate ions and urease, which are essential components of the present invention, and usually also contains undecomposed urea. By using solution A, it is possible to more effectively solidify the soil material.

[0024] When solution A is used, in addition to solution A, solution B containing urea and solution C containing a calcium salt are used as solutions containing essential components to prepare the solidifying agent.

[0025] In the pre-blending method, solution A, solution B, and solution C are blended to prepare a solidifying agent, but the present invention also includes an embodiment in which solution A is blended with solution BC containing urea and a calcium salt.

[0026] In the soil material blending method, it is important to mix solutions A and C in advance to form micelles of casein and calcium ions. In other words, it is important to use a mixed solution of solutions A and C, and solution B, but there is no particular restriction on the order in which they are added to the soil material.

[0027] The soil material fixing step in the soil material solidification method of the present invention may include a soil material slurry preparation step of mixing a solidifying agent with the soil material to prepare a soil material slurry, and a soil material slurry injection step of injecting the soil material slurry into a predetermined location. Also, the method may include a solidifying agent injection step of injecting a solidifying agent into the ground.

[0028] In addition, the soil material fixation process in the manufacturing method for solidified soil material of the present invention can be an embodiment that includes a soil material slurry preparation process in which a solidifying agent and soil material are mixed to prepare a soil material slurry, and a forming process in which the soil material slurry is formed into a predetermined shape and cured.

[0029] In the present invention, when the soil material and the solid agent are mixed, the following phenomenon occurs, and it is believed that the soil material is effectively solidified. That is, calcium ions contained in the casein micelles in the solidifying agent react with carbonate ions generated by the hydrolysis reaction of urea by urease, and calcium carbonate is generated between the particles of the soil material as a binder, and the soil material is solidified. The generated calcium carbonate contains a large amount of vaterite crystals (see FIG. 5), and it is considered that the vaterite crystals contribute greatly to the solidification of the soil material. Although some calcite crystals are observed in the generated calcium carbonate, it is preferable that the vaterite crystals are contained in a larger amount. The content ratio of vaterite crystals and calcite crystals can be semi-quantitatively estimated from the intensity ratio of the strongest lines of XRD. For example, the ratio (Iv / Ic) of the intensity of the strongest line of the vaterite crystals (Iv) to the intensity of the strongest line of the calcite crystals (Ic) is preferably 0.05 or more, more preferably 0.1 or more, even more preferably 0.2 or more, and particularly preferably 0.25 or more. In addition, since the main peak of calcite is around d = 3.03 Å (2θ = 29.4°) and the main peak of vaterite is around d = 3.30 Å (2θ = 27.0°), the intensities of these peaks are compared. In addition, the pre-mixing method results in a state in which a small amount of calcium carbonate precipitates in the solidifying agent, which further promotes the subsequent production of calcium carbonate and more effectively solidifies the soil material.

[0030] Furthermore, as described above, when using solution A containing a culture medium of urease-producing bacteria cultured in a medium containing casein and urea, it is believed that the negatively charged urease-producing bacteria adhere to positively charged casein micelles (containing calcium ions and / or calcium carbonate), and the attached urease-producing bacteria hydrolyze urea, causing the carbonate ions around the micelles to become supersaturated, thereby further promoting the formation of calcium carbonate crystals.

[0031] [Soil material solidification agent] The soil material solidification agent of the present invention is characterized by containing casein, calcium ions, carbonate ions, urea, and urease. The soil material solidification agent of the present invention is similar to the solidification agent described in the above-mentioned soil material solidification method and solidified soil material manufacturing method, so detailed description will be omitted. The soil material solidification agent of the present invention may be a combination of all essential components, or a combination of components in which some or all of the essential components are contained separately. Specifically, one preferred embodiment includes a solution A containing casein, carbonate ions, and urease, a solution B containing urea, and a solution C containing a calcium salt (including a solution BC containing urea and a calcium salt). Solution A is preferably a solution containing a culture solution of a urease-producing bacterium cultured in a medium containing casein and urea. EXAMPLES

[0032] The present invention will be described in detail below based on examples, but the scope of the present invention is not limited to these examples.

[0033] [Example 1 (Using urease-producing bacteria)] <Sand sample> Sand collected from Nakatajima Sand Dune in Hamamatsu City, Shizuoka Prefecture (hereinafter referred to as dune sand), sand collected from Asaba Beach in Fukuroi City, Shizuoka Prefecture (hereinafter referred to as beach sand), and Toyoura sand purchased from Toyoura Silica Industry Co., Ltd. were used as experimental samples. The dune sand and coastal sand were collected from two locations, one on the sea side, which is affected by seawater, and one on the land side, which is not affected by seawater. Toyoura sand is often used as standard sand for testing and research in geotechnical engineering.

[0034] Geomaterials are classified mainly based on grain size tests (JIS A 1204) (JGS0051 "Engineering Classification of Geomaterials"). According to this classification, all samples in this example are classified as "sand" with 5% or less fine particles (grain size 0.075mm or less) and 5% or less gravel (grain size 2mm to 75mm). Dune sand and coastal sand are mainly medium sand with an average grain size of 0.33-0.44mm, and Toyoura sand is mainly fine sand with an average grain size of 0.23mm.

[0035] <Preparation of Solution A (Microbial Culture Solution)> (Preparation of urea liquid medium) 30 g of SCD bouillon (Tryptosoya bouillon for general bacteria "Nissui", Nissui Pharmaceutical) was dissolved in 1000 ml of ultrapure water and sterilized in an autoclave at 121 °C for 15 minutes to prepare a liquid medium. The composition of SCD bouillon 30 g / L is 17.0 g / L casein peptone, 3.0 g / L soybean peptone, 5.0 g / L NaCl, 2.5 g / L glucose, and 2.5 g / L sodium dihydrogen phosphate (pH = 7.3 ± 0.2). This liquid medium was mixed with 0.66 mol / L urea solution (special grade, Kanto Chemical) sterilized with a filter (0.2 μm) in a volume ratio of 1:1 to prepare a 0.33 mol / L urea liquid medium (containing 15 g / L SCD bouillon).

[0036] (Preparation of urea agar medium) A mixture of 40 g of autoclave-sterilized SCD agar medium (Tryptosoya agar medium for general bacteria "Nissui", Nissui Pharmaceutical) and 900 ml of ultrapure water was mixed with 100 ml of filter-sterilized 0.33 mol / L urea solution, and an appropriate amount of this was immediately poured into a petri dish and allowed to solidify to prepare urea agar medium.

[0037] (Preparation of isolation culture of microorganisms (urease-producing bacteria culture)) 50 g of sand sample and 100 ml of urea liquid medium were placed in a sterile sample bag (Fisher Scientific), sealed with a sealer, and statically cultured in a 37°C incubator for 24 hours. The sand mixed medium was then centrifuged (4000 rpm, 5 min), and 0.5 ml of the supernatant and 50 ml of the newly prepared urea liquid medium were placed in a new sample bag, sealed with a sealer, and statically cultured again in a 37°C incubator for 24 hours. The same procedure was repeated once more, and the resulting supernatant was spread on a urea agar medium and statically cultured in a 37°C incubator for 24 hours. One independent colony that appeared on the agar medium was seeded in a urea liquid medium and statically cultured in a 37°C incubator for 24 hours. The microbial culture solution (urease-producing bacteria culture solution) thus obtained was used as "Solution A" in the subsequent solidification experiments. Two types of sand samples were used: dune sand and beach sand.

[0038] To confirm that the isolated bacteria were urease positive, one colony obtained on the agar was inoculated into 50 ml of urea liquid medium, and the ammonium ion concentration and pH in the liquid medium were measured after 0, 2, 5, 8.5, and 24 hours. As a result, the ammonium ion concentration and pH increased in all media, indicating promotion of urea hydrolysis. In addition, when the number of microbial cells in the culture solution after 5 and 24 hours was measured, cell proliferation was observed in all media. These results confirmed that the isolated bacteria were urease positive.

[0039] In addition, DNA sequence analysis and molecular phylogenetic analysis (16S rDNA-Full) of the isolated bacteria that tested positive for urease were conducted, and the taxonomic group to which each sample belonged was estimated to belong for both the land and sea sides of the dune sand to the genus Sporosarcina (related species: Sporosarcina pasteurii, Sporosarcina luteola, Sporosarcina soli), while for the seaside and landside beach sand to the genus Virgibacillus (related species: Virgibacillus proomii) and Lederbergia (related species: Lederbergia lenta) (analysis commissioned to Techno Suruga Lab Co., Ltd.).

[0040] <Preparation of solution B and solution C (solution BC)> A mixed solution of 1.00 mol / L calcium chloride (special grade, Kanto Chemical) and 0.66 mol / L urea (special grade, Kanto Chemical) was prepared as "Solution BC."

[0041] <Preparation of solidifying agent> The above-prepared "Solution A" and "Solution BC" were mixed in a volume ratio of 1:1 to produce a white dispersible mixture of casein micelles and calcium carbonate (CaCO3) in the solution, thereby preparing the solidifying agent.

[0042] <Solidification of soil material (sand)> Following preparation of the solidification agent, a specified amount of sand sample was mixed with it to create a mixed slurry of sand and solidification agent.

[0043] Next, the mixed slurry was poured into a plastic mold with a diameter of 50 mm and a height of 100 mm so as to obtain a predetermined relative density, and the mold was left standing upright at a constant temperature of 37°C for 24 to 48 hours. The mixing ratio of the solution and sand sample when preparing the mixed slurry was determined according to the initial relative density of the specimen.

[0044] After the curing period, the solidified specimens were removed from the mold and submerged in approximately 1 L of distilled water per specimen. After leaving them for a certain period of time, the water was replaced and the specimens were submerged again three times to wash away excess salts from the specimens. <Strength evaluation> (test) A triaxial test (JGS 0524-2009 "Consolidation and drainage (CD) triaxial compression test of soil") was conducted to evaluate the strength of the solidified sand samples (hereafter referred to as "solidified specimens"). The solidified specimens were washed with water and then subjected to a CD test while still wet. The specimens were placed in a triaxial cell and then fully saturated by passing deaerated water through them. The saturated specimens were isotropically consolidated at effective confining pressures of 30, 50, and 100 kPa, and then axially compressed at a strain rate of 0.1% / min. The axial compressive force was measured with a load cell and the drainage volume was measured with a differential pressure gauge, to evaluate the relationship between the axial stress and volumetric strain relative to the axial strain.

[0045] (result) Using this solidification method, solidification was confirmed in three samples: beach sand, dune sand, and Toyoura sand. Figure 1 shows the relationship between the principal stress difference (=axial stress difference) and axial strain, and between the volumetric strain and axial strain for the CD test results for untreated and solidified dune sand specimens at effective confining pressures of 30, 50, and 100 kPa. The legend for Figure 1 also shows the relative density Dr. Dr is an index that indicates the state of compaction of the soil in question, between its densest and loosest conditions. Fujita (1968) defined D as r ≦35% loose sand, 35% <D r <65% medium-dense sand, D r Sand with a density of 65% or more is classified as dense. The test results in Figure 1 are a comparison of medium-density sand specimens with Dr = 40-56%.

[0046] For the solidified specimens, the principal stress difference rose sharply immediately after the axial stress loading under all effective confining pressures, reaching a peak at small strains (0.28-0.59%) (Figure 1 (a) upper panel). This sudden change in stress at small strains can be attributed to solidification (=cementation) by calcium carbonate. The volumetric deformation associated with shear showed a slight tendency to shrink at the beginning of the shearing process, and then showed positive dilatancy (behavior in which the volume changes (expands or shrinks) when subjected to shear force) as the specimens softened (Figure 1 (a) lower panel). Comparing the test results for the untreated and solidified specimens, the maximum principal stress difference increased with solidification at all effective confining pressures, becoming 4.1 times larger at an effective confining pressure of 30 kPa, 2.7 times larger at 50 kPa, and 1.8 times larger at 100 kPa. The increase in the maximum principal stress difference decreased with increasing confining pressure, suggesting the possibility of partial collapse of precipitated calcium carbonate crystals due to confining pressure. The volumetric strain showed positive dilatancy regardless of whether the specimens were solidified or not, but the degree of dilatancy was reduced in the solidified specimens compared to the untreated specimens.

[0047] Furthermore, when the specimens were observed at the end of the shear stress, the pattern of volumetric deformation was different between the solidified and untreated specimens (Fig. 2). Generally, triaxial tests on sand show a "barrel-shaped deformation" as seen in untreated specimens (Fig. 2(b)), whereas the solidified specimens did not change significantly from their initial shape and showed shear failure with a slip surface (Fig. 2(a)).

[0048] In addition, from the SEM-EDX (SU3500, Hitachi High-Technologies) images of the solidified sand specimen, it was observed that spherical crystalline material (50-100μm) uniformly covered the soil particle surface (Fig. 3). Furthermore, only the spherical crystalline material was extracted and mineral analysis was performed by XRD (RINT2100, Rigaku) ​​(top of Fig. 4) and crystal observation was performed by digital microscope (RH-2000, MXB2500REZ, HiROX) (Fig. 5). It was found that the crystalline material precipitated by this method is a composite material of vaterite and calcite (both are homogeneous heteromorphs of CaCO3). It is considered that the granular crystals are vaterite and the non-granular crystals are calcite.

[0049] As a comparative example, when an experiment similar to that in Example 1 was carried out without adding casein peptone (SCD bouillon), the only calcium carbonate crystals that precipitated due to the precipitation of carbonate ions and calcium ions were calcite, and no granular (vaterite) crystals were observed (lower diagram in Figure 4), and the soil material did not solidify (Figure 6).

[0050] In addition, from the relationship between the mean effective stress at the maximum axial stress and half of the principal stress difference, the strength constant (internal friction angle φ d and adhesive strength c d ) was calculated, and the solidification d The expression of was confirmed (Figure 7, Table 1).

[0051] [Table 1]

[0052] φ of solidified specimen d The internal friction angle φ of the untreated specimen after correction was smaller than that of the untreated specimen, but the stress-dilatancy equation (Equation (1)) of Rowe (1962) was applied. f is φ f = 27.15°, and the φ of the solidified specimen d = 27.17°, which is very close to the value.

[0053]

number

[0054] where σ'1 / σ'3 is the principal stress ratio, 1-dε v / dε1 is the principal strain increment ratio (volumetric strain ε v (The compression side is positive.) In addition, in equation (1), c d = 0, it cannot be directly applied to solidified specimens.

[0055] To compare the manifestation of the solidification effect depending on the initial relative density Dr of the specimen, the principal stress difference-axial strain and volumetric strain-axial strain (0-3%) of the triaxial test results at an effective confining pressure of 50 kPa for untreated and solidified specimens are shown in Fig. 8. As shown in the figure legend, five solidified specimens with extremely loose to medium density Dr = -12-40% were compared. Regardless of the relative density Dr, the principal stress difference increased sharply at small strains of axial strains of 1% or less, and then decreased (Fig. 8 (a)). On the other hand, dilatancy was affected by Dr regardless of whether it was untreated or solidified, and tended to shrink in volume at Dr = 21% or less and expand in volume at Dr = 34% or more due to strain softening (Fig. 8 (b)). A positive correlation was observed between Dr and the maximum principal stress difference, and a large improvement in strength due to solidification was observed even in the loosely packed specimens.

[0056] [Example 2 (Urease used)] A "urease solution" was used instead of the "urease-producing bacteria culture solution" in Example 1. The "urease solution" was prepared so as to have a solute composition similar to that of the "urease-producing bacteria culture solution."

[0057] (Preparation of urease solution) 0.15 g / 100 ml of enzyme (urease) was dissolved in a mixed solution (pH = 10.3 ± 0.2) of 0.33 mol / L sodium bicarbonate (special grade, Kanto Chemical) and 15 g / L SCD bouillon (Nissui). 1 M NaOH aqueous solution was used to adjust the pH. The enzyme was mixed into the urease solution just before use. The enzyme used was 5000 U / g urease (derived from jack bean, Kanto Chemical).

[0058] (Solution BC) The same solution as Solution BC in Example 1 was used.

[0059] When the above solutions A and BC were mixed in a 1:1 ratio, white micelles were produced as in Example 1. 30 ml of this micelle mixture was added to 5.0±0.04 g of dune sand in a cylindrical plastic container, stirred, and allowed to stand at 37° C. for 24 hours.

[0060] Figure 9 (left) shows the state of the sand sample after it was removed from the solution after 24 hours and washed with water. Figure 9 (right) shows the case where a culture solution of urease-producing bacteria was used. When urease was used, the solidification of the soil material was also confirmed. Furthermore, when only the crystalline material was extracted and mineral analysis was performed by XRD (RINT2100, Rigaku) ​​(center of Figure 4), it was found that the crystalline material was a composite material of vaterite and calcite (both are homogeneous and heteromorphic species of CaCO3).

[0061] [Study on the content ratio of vaterite and calcite in precipitated calcium carbonate crystals] From the intensity ratio of the strongest XRD lines of the target minerals, it is possible to semi-quantitatively estimate the relative content of the minerals mixed. For example, in a sample consisting of two polymorphic phases a and b, the proportion of phase a, Fa, can be quantitatively expressed by the following equation:

[0062] Fa = 1 / {1+ K (I b / I a )}

[0063] This value is the intensity ratio of the two phases (I b / Ia ) and obtain the value of the constant K, which is the absolute intensity ratio I oa / I ob and is determined by measuring standard samples.

[0064] Here, for calcium carbonate precipitated in Example 1 (casein + microorganisms), calcium carbonate precipitated in Example 2 (casein + enzyme reagent), and calcium carbonate precipitated in Comparative Example (enzyme reagent only), the strongest line intensities of calcite and vaterite in XRD are shown in Table 2. It is known that the main peak of calcite in X-ray diffraction appears near d = 3.03 Å (2θ = 29.4°), and the main peak of vaterite appears near d = 3.30 Å (2θ = 27.0°).

[0065] [Table 2]

[0066] In the X-ray diffraction, only the peaks specific to calcite appeared in the crystalline substance precipitated using only the enzyme of the comparative example. On the other hand, in the crystalline substances of Examples 1 and 2, peaks specific to vaterite appeared in addition to calcite. Assuming that the precipitated crystalline substance contains only two types of minerals, calcite and vaterite, the intensity ratio of vaterite to calcite (Iv / Ic) is larger in Example 1 using a microorganism than in Example 2 using an enzyme reagent, and it can be determined that the proportion of vaterite in the precipitated crystals is high. [Industrial Applicability]

[0067] The method of the present invention can be used for protecting the slopes of seawalls, etc., and is therefore industrially useful.

Claims

1. a solidifying agent preparation step of preparing a solidifying agent containing casein, calcium ions, carbonate ions, urea, and urease; a soil material solidification step of contacting the solidification agent with the soil material to solidify the soil material; 1. A method for solidifying soil material, comprising:

2. a solidifying agent preparation step of preparing a solidifying agent containing casein, calcium ions, carbonate ions, urea, and urease; a soil material solidification step of contacting the solidification agent with the soil material to solidify the soil material; 1. A method for producing a solidified soil material comprising the steps of:

3. 3. The method according to claim 1, wherein the solidifying agent, casein, and calcium ions form micelles.

4. The solidifying agent preparation step comprises:

3. The method according to claim 1 or 2, characterized in that the solidifying agent is prepared by mixing solution A containing casein, carbonate ions and urease, solution B containing urea, and solution C containing a calcium salt.

5. 5. The method according to claim 4, wherein said solution A contains a culture medium of a urease-producing bacterium cultured in a medium containing casein and urea.

6. 5. The method of claim 4, wherein the calcium salt of solution C is calcium chloride, calcium acetate or calcium nitrate.

7. The soil material solidification step includes: a soil material slurry preparation step of mixing the solidifying agent and soil material to prepare a soil material slurry; A soil material slurry injection process of injecting the soil material slurry into a predetermined location; 2. The method of claim 1, further comprising:

8. The soil material solidification step includes:

2. The method according to claim 1, further comprising a step of injecting the solidification agent into the ground.

9. 3. The method according to claim 1, wherein in the soil solidification step, the solidification agent forms vaterite crystals of calcium carbonate to solidify the soil.

10. A soil material solidification agent comprising casein, calcium ions, carbonate ions, urea, and urease.

11. 11. The soil solidification agent according to claim 10, wherein the casein and calcium ions form micelles.

12. 11. The soil solidification agent according to claim 10, comprising: solution A containing casein, carbonate ions and urease; solution B containing urea; and solution C containing a calcium salt.

13. 13. The soil solidifying agent according to claim 12, wherein the solution A contains a culture solution of a urease-producing bacterium cultured in a medium containing casein and urea.

14. 14. The soil solidification agent according to claim 12 or 13, characterized in that the calcium salt of said solution C is calcium chloride, calcium acetate or calcium nitrate.

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