Method for producing a modified material for expansive soil, and method for modifying expansive soil.

Abstract

The present invention is a modifier for expansive soil that contains at least one selected from salts, cements, and limes in expansive soil.　In addition, the present invention is a modified expansive soil that contains at least expansive soil and a modifier for expansive soil.　In addition, the present invention is a method for producing a modified expansive soil in which the modifier for expansive soil is added to and mixed with expansive soil and a modified expansive soil is produced, preferably a method for producing a modified expansive soil in which 0-10 mass parts of salts, 0-30 mass parts of cements, and 0-20 mass parts of limes are added and mixed per 100 mass parts of expansive soil as a modifier for expansive soil, and a modified expansive soil is produced (provided that the sum of the amounts of salts, cements, and limes added is not 0 mass parts).

Description

Technical Field

[0001] The present invention relates to a modifier for expansive soil that increases the compressive strength of expansive soil and suppresses the swelling and shrinkage properties of expansive soil, a modified product of expansive soil modified using the modifier for expansive soil, and a method for manufacturing the modified product of expansive soil. In the specification of the present application, expansive soil refers to earth and sand that swells due to moisture absorption and water absorption and shrinks due to drying.

Background Art

[0002] The above-mentioned expansive soils include bentonite and black cotton soil (black peat soil, Black Cotton Soil, hereinafter referred to as "BCS"). Among these, BCS is widely present in tropical and subtropical regions and is a soil containing swelling clay minerals such as montmorillonite. This BCS swells and becomes muddy when it contains moisture and shrinks when it dries. As a result, when a road is laid on the ground leaving BCS, the BCS repeats shrinkage and swelling due to the change in dryness and wetness between the dry season and the rainy season, causing cracks in the road and the road to collapse (see Non-Patent Document 1).

[0003] Currently, the main countermeasure against road collapse caused by BCS is to replace the surface layer of the ground containing BCS with high-quality earth and sand. For example, Non-Patent Document 1 proposes a method of arranging high-quality replacement soil with a thickness of 1 m directly under the road planned to be laid and arranging it with a depth of 3 m on both sides of the road to suppress the change in the water content (i.e., the change in volume) of the remaining BCS (see the BCS countermeasure work adopted in the project of Fig.-4).

[0004] In addition, Non-Patent Document 2 proposes the following methods a) to g) as means for suppressing the occurrence of cracks in structures built on BCS in India. a) A method of removing the expansive soil and installing non-expansive soil in the foundation of the structure b) A method of minimizing differential settlement by using a reinforced and highly rigid foundation c) A method of increasing the flexibility of the structure to allow large differential settlement d) A method of pre-moistening expansive soil to minimize subsequent changes in water content. e) A method of applying a large stress to the foundation to balance it with the expansion pressure. f) A method of placing a suitable non-stick layer between the expansive soil and the foundation. g) Foundation and ground improvement methods using piers, piles, and beams Furthermore, in India, the under-reamed pile method and the multi-under-reamed pile method for larger structures are widely used (see Figure 11, Construction Sequence of Multi-Under-Reamed Piles).

[0005] However, I believe the above method has the following problems. i) Replacing with high-quality soil requires the transport of replacement soil and the removal of the replaced BCS. Furthermore, in road construction projects in urban areas, it is necessary to secure a place to store the removed BCS. ii) The underreamed pile method is uneconomical for small-scale structures, therefore, a simpler and cheaper method for constructing foundations is needed (see "8. Conclusion" on page 51 of Non-Patent Document 2). [Prior art documents] [Non-patent literature]

[0006] [Non-Patent Document 1] Okita et al., "A Study on Countermeasures for Expanding Soil in Ethiopia," Proceedings of the 69th Annual Scientific Conference of the Japan Society of Civil Engineers (September 2014), pp. 1331-1332. [Non-Patent Document 2] D. Mohan et al., "Black Cotton Soil of India," Soil and Foundation, 26-11(248), November, 1978, pp. 47-51. [Overview of the project] [Problems that the invention aims to solve]

[0007] Therefore, the present invention aims to provide a method for modifying expansive soil to suppress its swelling and shrinkage, and to produce a modified expansive soil that is strong and resistant to collapse. [Means for solving the problem]

[0008] Therefore, the present inventors diligently studied to achieve the above objectives and found that an expandable soil modifier, an expandable soil modifier, and a method for producing an expandable soil modifier having the following configuration can achieve the above objectives, and thus completed the present invention described below.

[0009] [1] A method for producing an expandable soil modifier, comprising at least the following steps (A) to (D) and the divided addition of the following expandable soil modifier to produce the following expandable soil modifier. (A) Expanding soil 100 parts by mass In contrast, Of the following, 0 to 10 parts by mass of table salt or seawater (in terms of salinity), 0 to 30 parts by mass of Portland cement, and 0 to 20 parts by mass of slaked lime, (A-1) An expansive soil modifier comprising at least one selected from seawater, Portland cement, and slaked lime. or, (A-2) Expandable soil modifier containing at least two ingredients selected from table salt and Portland cement or slaked lime. The process of preparing a primary mixture involves adding and mixing the ingredients to produce a primary mixture. (B) After curing the primary mixture, the primary mixture is crushed to produce a crushed product, which is the process for producing a crushed product of the primary mixture. (C) The above-mentioned crushed material 100 parts by mass of expandable soil inside In contrast, Contains at least 0 to 30 parts by mass of Portland cement and 0 to 20 parts by mass of slaked lime. Expandable soil modifier , the above-mentioned crushed material The process of preparing a secondary mixture involves adding and mixing secondary ingredients to create a secondary mixture. (D) Compact the above secondary mixture To obtain a modified material for expansive soil The compaction process of the secondary mixture. [2] A method for producing an expandable soil modifier according to [1] above, further comprising (A) a compaction step of compacting the primary mixture prepared in the primary mixture preparation step. [3] A method for producing an expandable soil modifier according to [1] above, wherein the amount of the above-mentioned modifier added in stages is 0.01 to 20 parts by mass for primary addition and 1 to 20 parts by mass for secondary addition, per 100 parts by mass of expandable soil. [4] The method for producing a modified expansive soil according to [1] above, wherein the curing period of the above primary mixture is 7 days to 1 year. [5] The method for producing a modified expansive soil according to [1] above, wherein the particle size of the above crushed material is 200 mm or less. [6] The method for producing a modified expansive soil according to [1] above, wherein water is added at the time of the first addition of the above modifier in the case of (a) below, and water is added at the time of the second addition of the above modifier in the case of (b) below. (a) When it is difficult or impossible to stir and mix the modifier due to the high viscosity of the expansive soil (b) When the compressive strength of the secondary mixture after the above curing is 0.5 N / mm 2 or more in the case of crushing [7] The method for producing a modified expansive soil according to any one of [1] to [6] above, wherein the above expansive soil is black cotton soil. [8] A method for modifying an expansive soil, which modifies the following expansive soil by adding the following modifier for expansive soil in portions through at least the following steps (A) to (D). (A) Expansive soil 100 parts by mass To which Of the following, 0 to 10 parts by mass of table salt or seawater (in terms of salinity), 0 to 30 parts by mass of Portland cement, and 0 to 20 parts by mass of slaked lime, (A-1) An expansive soil modifier comprising at least one selected from seawater, Portland cement, and slaked lime. or, (A-2) Expandable soil modifier containing at least two ingredients selected from table salt and Portland cement or slaked lime. is added in the first addition and mixed to produce a primary mixture, a step of producing a primary mixture (B) After curing the above primary mixture, the primary mixture is crushed to produce a crushed material, a step of producing a crushed material of the primary mixture (C) To the above crushed material 100 parts by mass of expandable soil inside To which Contains at least 0 to 30 parts by mass of Portland cement and 0 to 20 parts by mass of slaked lime. A modifier for expansive soil is , the above-mentioned crushed material added in the second addition and mixed to produce a secondary mixture, a step of producing a secondary mixture (D) Compact the above secondary mixture To obtain a modified material for expansive soil A step of compacting the secondary mixture [9] Further, the method for modifying an expansive soil according to [8] above, including a compacting step of compacting the primary mixture produced in the step of producing the primary mixture.

[10] The method for modifying expansive soil according to [8] above, wherein the amount of the above-mentioned modifier added in stages is 0.01 to 20 parts by mass for primary addition and 1 to 20 parts by mass for secondary addition, per 100 parts by mass of expansive soil.

[11] The method for modifying expansive soil as described in [8] above, wherein the curing period for the primary mixture is 7 days to 1 year. [Effects of the Invention]

[0010] In the present invention, the method for producing a modified product of expansive soil using the above-mentioned modifier can modify the expansive soil to suppress swelling and shrinkage of the soil and produce a modified product with high strength. [Modes for carrying out the invention]

[0011] As described above, the present invention relates to an expandable soil modifier, an expandable soil modifier, and a method for producing an expandable soil modifier. The present invention will be described in detail below.

[0012] 1. Expandable soil modifier The above-mentioned expansive soil modifier contains at least one selected from salts, cements, and limes. The above-mentioned expansive soil is a type of soil mainly containing montmorillonite that expands when it absorbs water and contracts when it dries. In the present invention, an example of the expansive soil is black cotton soil. For example, black cotton soil has a liquid limit (W L ) is 46-97%, and the plasticity index (I P With a liquid-to-plastic limit of 21-63%, this soil has relatively high liquid and plastic limits. Furthermore, the above-mentioned salts are one or more selected from alkali metal salts and alkaline earth metal salts, specifically one or more selected from sodium chloride, table salt, potassium chloride, calcium chloride, magnesium chloride, sodium carbonate, and potassium carbonate, etc. Furthermore, the present invention also allows the use of seawater and wood ash containing these salts. For example, if road construction is along the coast, seawater can be used, and if it is in a grassland, forest, or granary area, wood ash produced by burning vegetation can be used.

[0013] The amount of salts added is preferably 0 to 10 parts by mass per 100 parts by mass of expandable soil. If the amount of salts added is within the above range excluding 0 parts by mass, the liquid limit of the expanded soil after modification will decrease and the dry density will increase, thereby suppressing shrinkage and swelling. Furthermore, if there is no need to modify the liquid limit and / or dry density of the expanded soil, the addition of salts is unnecessary (i.e., 0 parts by mass). The amount of salts added is more preferably 1 to 8 parts by mass per 100 parts by mass of expanded soil.

[0014] Furthermore, the above-mentioned cements include one or more selected from blast furnace cement type A, blast furnace cement type B, blast furnace cement type C, Portland cement, silica cement, fly ash cement, eco-cement, and cement-based solidifying agents. Here, cement-based solidifying agents are composite materials with cement as the base material. Other solidifying components and their proportions are determined according to the difficulty of solidification, such as for general soft soil, special soil (general-purpose type), and high-organic soil, as well as the conditions of the solidification site. For example, commercially available cement-based solidifying agents include GeoSet (registered trademark, manufactured by Taiheiyo Cement Corporation) 200 for general-purpose use and GeoSet (registered trademark, manufactured by Taiheiyo Cement Corporation) 225 for high-organic soil use. Among the cements mentioned above, blast furnace cement type B, Portland cement, and cement-based solidifying agents are suitable as modifiers for expansive soils due to their low cost and high solidifying performance.

[0015] The amount of cement added is preferably 0 to 30 parts by mass per 100 parts by mass of the expansive soil. If the amount of cement added is within the above range excluding 0 parts by mass, the strength development is high and the swelling and shrinkage rates are low. More preferably, the amount of cement added is 10 to 20 parts by mass per 100 parts by mass of the expansive soil.

[0016] Furthermore, the above-mentioned limes are one or more selected from slaked lime, quicklime, calcium hydroxide, calcium oxide, gypsum, and calcium sulfate. Of these limes, slaked lime or calcium hydroxide are preferred because they exhibit high strength development and are easy to handle. The amount of lime added is preferably 0 to 20 parts by mass per 100 parts by mass of expansive soil. If the amount of lime added is within the above range excluding 0 parts by mass, the strength development is high and the swelling rate and shrinkage rate are low. The amount of lime added is more preferably 5 to 15 parts by mass per 100 parts by mass of expansive soil.

[0017] 2. Method for producing a modified material for expansive soil The present invention provides two methods for producing a modified material for expansive soil: a method in which the modifier is added all at once (all-at-once addition method), and a method in which the modifier is added in two parts (partial addition method). Generally, if the amount of modifier added is the same, the modified material produced by the partial addition method has higher strength and lower swelling and shrinkage than the modified material produced by the all-at-once addition method. The all-at-once addition method is a commonly used addition method and does not require explanation. Therefore, only the partial addition method will be explained.

[0018] The method for adding the modifier in stages includes at least (A) a step of preparing a primary mixture, (B) a step of preparing a crushed product of the primary mixture, (C) a step of preparing a secondary mixture, and (D) a step of compacting the secondary mixture. Each of the above steps will be described below.

[0019] (A) Preparation of the primary mixture The process involves adding the modifier to the expandable soil and mixing to produce a primary mixture. The primary addition ratio of the modifier is preferably 0.01 to 20 parts by mass per 100 parts by mass of expandable soil. When the primary addition ratio of the modifier is within this range, the liquid limit of the expanded soil modification is reduced, the dry density is increased, the strength of the modification is improved, and swelling and shrinkage of the modification are suppressed. More preferably, the primary addition ratio of the modifier is 5 to 15 parts by mass per 100 parts by mass of expandable soil. The equipment used to mix the expansive soil with the primary or secondary additive modifier is not particularly limited and is generally a mixer used for mixing concrete or mortar, such as a tiltable mixer, forced mixer, drum mixer, gravity mixer, and hand mixer. On-site mixing equipment may include a backhoe, bucket mixer, and a batch or continuous mixer specifically for soil cement. Furthermore, the process of preparing the primary mixture may optionally include a step of compacting the primary mixture. The compaction method used in the present invention is not particularly limited, and examples include compaction using a vibratory roller or a vibratory damper. Also, if the strength of the modifier is insufficient, it is advisable to add more modifier to the crushed material and compact it in this step.

[0020] (B) Process for preparing the pulverized primary mixture The process involves curing the primary mixture and then crushing it to produce crushed material. While the curing method is not particularly limited, air-drying is preferred because it facilitates curing large road areas. The curing period is preferably 7 days to 1 year, depending on the type and amount of modifying agent added. If the curing period falls within this range, the cured primary mixture will have sufficient strength to be crushed. Furthermore, the compressive strength of the primary mixture after the curing process is preferably 0.2 to 4.0 N / mm². 2 The compressive strength is 0.2 N / mm². 2 Below 1.2 N / mm², the strength of the above secondary mixture may not reach a level that allows for crushing (it may turn into mud when pressurized). 2 If the compressive strength exceeds this value, crushing may become difficult, or compaction after crushing may become difficult. The compressive strength is preferably 0.4 to 1.0 N / mm². 2 That is the case. Furthermore, the particle size of the crushed material is preferably 200 mm or less. If the particle size exceeds 200 mm, compaction becomes difficult. The particle size is preferably 150 mm or less. Furthermore, the crushing method is not particularly limited, but examples include crushing the primary mixture after the curing process using the bucket or tracks of a backhoe, or crushing it using a special crusher equipped with a sieve.

[0021] (C) Process for preparing the secondary mixture This step involves adding the above-mentioned modifying agent to the above-mentioned crushed material and mixing it to produce a secondary mixture. The secondary addition ratio of the above-mentioned modifier is 1 to 20 parts by mass per 100 parts by mass of the above-mentioned expansive soil. If the secondary addition ratio of the above-mentioned modifier is within the above range, the dry density of the modified material of the expansive soil will increase, as in the case of the primary addition, the strength of the modified material will improve, and swelling and shrinkage will be suppressed. The secondary addition ratio of the above-mentioned modifier is preferably 5 to 15 parts by mass per 100 parts by mass of the expansive soil.

[0022] (D) Compaction process of the secondary mixture This step involves compacting the above-mentioned secondary mixture. Furthermore, in this step, it is preferable to cure the mixture after compaction to prevent freezing in winter and drying in summer. Examples of such curing include the use of curing sheets or mats, and the combined use of these curing methods with watering or heat curing, or air drying.

[0023] In this invention, if it is necessary to adjust the viscosity of the expansive soil and the strength of the modified material, water may be added during the primary addition of the modifier and / or during the secondary addition of the modifier. The conditions for adding water are as follows: in case (a) below, water is added during the primary addition, and in case (b) below, water is added during the secondary addition. (a) When the viscosity of the expansive soil is high, making it difficult or impossible to mix the modifier. (b) The compressive strength of the secondary mixture after the curing process is 0.5 N / mm² at the time of crushing. 2 In the above cases Here, the case where stirring and mixing of the modifier is difficult or impossible due to the high viscosity of the expansive soil cannot be expressed in a single, definitive way, as stirring and mixing depends on the performance of the mixing equipment. However, it refers to cases where stirring and mixing is not possible or does not result in uniform mixing. The water used can be tap water, river water, lake water, seawater, or treated wastewater. The amount of water to be added should be determined by actually preparing the mixture using the water to be used. When using water other than tap water, it is preferable to confirm that it does not adversely affect the solidification performance. [Examples]

[0024] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. 1.Materials used Table 1 shows the materials used in this embodiment. Table 2 shows the properties of black cotton soil a, bentonite, and black cotton soil b used in this embodiment.

[0025] [Table 1]

[0026] [Table 2]

[0027] 2. Measurement of the swelling rate of expansive soils due to salts 80 ml of aqueous solutions of salt a at various concentrations (shown in Table 3 as the amount of salt a added) were each placed in a 100 ml graduated cylinder. Next, 40 g of black cotton soil a (expandable soil) having a natural water content (water content of soil in its natural state) was dropped into the aqueous solution, and the rise in water level was immediately read on the graduated cylinder. The increased volume was determined as the volume of black cotton soil a before water absorption. Next, the mixture of the aqueous solution and black cotton soil a was stirred, and then the mixture was left to stand for 1 day and 7 days. The volume of black cotton soil a after water absorption was determined by reading the scale on a graduated cylinder at the boundary between the water-absorbed and swollen black cotton soil a and the aqueous solution, and the swelling rate of black cotton soil a was calculated using the following formula (1). The results are shown in Table 3. Swelling rate of Black Cotton Soil a (%) = 100 × (Volume of Black Cotton Soil a after water absorption - Volume of Black Cotton Soil a before water absorption) / Volume of Black Cotton Soil a before water absorption ... (1) As shown in Table 3, the swelling rate of black cotton soil a decreases with increasing amounts of added salt a, indicating that salt a can suppress the swelling of black cotton soil a.

[0028] [Table 3]

[0029] 2. Measurement of compressive strength, swelling rate, and shrinkage rate of modified materials produced by batch addition of modifiers. (1) Production of modified products by batch addition of modifying agents Bentonite (expandable soil) was mixed using an electric mixer (manufactured by Hitachi Koki) while adding kneading water without sodium chloride b, or kneading water containing sodium chloride b, until the bentonite reached its liquid limit (the water content at the boundary when it transitions from a plastic state to a liquid state) to obtain a bentonite slurry. Incidentally, the above liquid limit was 169% in Examples 4-6, 90% in Examples 7-9, 85% in Examples 10-12, and 169% in Comparative Example 2. In this specification, the measurement of the liquid limit was performed in accordance with JGS T 142-1997, "Method for testing the liquid limit of soil using a fall cone." Next, cement a (cement type) and slaked lime a (lime type) were added to the slurry in the amounts shown in Table 4, and the mixture was kneaded in a Hobart-type mixer to produce a modified product.

[0030] (2) Measurement of the compressive strength of the modified material The above-mentioned modified material was placed in a mold with an inner diameter of 50 mm and a height of 100 mm, and specimens were sealed and cured. The compressive strength of the specimens was measured at 7 days and 28 days of age in accordance with JIS A 1216 "Method for uniaxial compression testing of soil". The results are shown in Table 4. As shown in Table 4, compressive strength could be measured in Examples 4 to 12, but not in Comparative Example 2.

[0031] (3) Measurement of the swelling rate and shrinkage rate of the modified material The residues of the modified material at 7 days and 28 days of age, generated during the above-mentioned compression strength measurements, were crushed by passing them through a sieve with a nominal mesh size of 9.5 mm to obtain the crushed material. Next, in the same manner as the measurement of the swelling rate of the expansive soil with the salts described above, the pulverized material was dropped into water in a graduated cylinder, and the increased volume was determined as the volume of the expansive soil before water absorption. Furthermore, after stirring the mixture of water and pulverized material, the mixture was left to stand for 3 hours and 7 days, and the volume of the pulverized material after water absorption was measured. The swelling rate of the pulverized material (modified material) was calculated using the following formula (2). These swelling rates are shown in Table 4. As shown in Table 4, the swelling rates in Examples 4 to 12 are all lower than those in Comparative Example 2. Swelling rate of the pulverized material (%) = 100 × (Volume of pulverized material after water absorption - Volume of pulverized material before water absorption) / Volume of pulverized material before water absorption ... (2)

[0032] Next, the crushed material was filled into a boat-shaped container made by splitting a cylinder with an inner diameter of 50 mm and a height of 100 mm lengthwise. After drying in an air-dried room for 1 day, 7 days, and 21 days, the container was removed, its length and width were measured, and the shrinkage rate of the container (modified material) was calculated using the following formula (3). These shrinkage rates are shown in Table 4. Shrinkage rate of the filling material (%) = 100 × (Volume of the filling material before drying - Volume of the filling material after drying) / Volume of the filling material before drying ... (3) As shown in Table 4, the shrinkage rate in Examples 4-12 is equivalent to or less than that in Comparative Example 2. Furthermore, the starting point for measuring the swelling and shrinkage rates of the above-mentioned modified material is the time of measurement of the compressive strength (i.e., the time when the above-mentioned residue is generated).

[0033] [Table 4]

[0034] 3. Production of a modified product by dividing and adding the modifier, and measurement of the compressive strength, swelling rate, and shrinkage rate of the modified product. (1) Preparation of the primary mixture and its pulverized product In the same manner as in the production of the modified product by the bulk addition of the above-mentioned modifiers, a bentonite slurry was prepared by kneading the bentonite using the above-mentioned electric stirrer while adding kneading water without sodium chloride b, or kneading water containing sodium chloride b, until the bentonite reached its liquid limit. Incidentally, the liquid limit values ​​were 169% in Examples 13-17, 90% in Examples 18-22, and 85% in Examples 23-26. Next, according to the formulation in Table 5, the modifier was added to the bentonite slurry and mixed to prepare a primary mixture. Furthermore, the primary mixture was placed in a polyethylene bag and cured in a sealed state for 28 days. After that, the primary mixture was crushed through a sieve with a nominal mesh size of 9.5 mm to prepare a crushed primary mixture.

[0035] [Table 5]

[0036] (2) Preparation of modified material and measurement of compressive strength, swelling rate, and shrinkage rate Next, according to the formulation in Table 5, the modifier was added to the pulverized primary mixture and mixed in a Hobart mixer to produce a modified material (secondary mixture). Furthermore, specimens molded from the secondary mixture in a mold with an inner diameter of 50 mm and a height of 100 mm were sealed and cured, and the compressive strength of the modified material (secondary mixture) at 7 days and 28 days of age was measured in the same manner as above. In addition, the residue of the modified material at 7 days and 28 days of age obtained from the compressive strength measurement was crushed through a sieve with a nominal mesh opening of 9.5 mm, and the swelling rate and shrinkage rate of the crushed material were measured in the same manner as above. These results are shown in Table 5. As shown in Table 5, all examples exhibited high strength and low swelling and shrinkage rates.

[0037] (3) Measurement of compressive strength, swelling rate, and shrinkage rate of modified material using black cotton soil a Using black cotton soil a, salt a, and cement b, the compressive strength, swelling rate, and shrinkage rate of the modified material were measured in the same manner as described above, according to the formulations shown in Table 6. These results are shown in Table 6. As shown in Table 6, Examples 27-34 showed higher compressive strength and lower swelling and shrinkage rates compared to Comparative Example 3. Incidentally, the test water content was 33.3% for Examples 27-30, 52.6% for Examples 31-34, and 22.5% for Comparative Example 3.

[0038] [Table 6]

[0039] (4) Measurement of compressive strength, swelling rate and shrinkage rate of modified material using black cotton soil b Using black cotton soil b, seawater, and slaked lime b, the compressive strength, swelling rate, and shrinkage rate of the modified material were measured in the same manner as described above. These results are shown in Table 7. As shown in Table 7, the longer the air-drying period of the modified material, the higher the compressive strength and the smaller the swelling and shrinkage.

[0040] [Table 7]

[0041] (5) Measurement of compressive strength, swelling rate and shrinkage rate of modified material using black cotton soil b A primary mixture was prepared by adding 2.6 parts by mass of slaked lime to 100 parts by mass of black cotton soil b and mixing. Next, the primary mixture was air-dried and cured for the period shown in Table 8. The amounts of water and cement b shown in Table 8 were then added to the primary mixture to produce a modified product (secondary mixture). Furthermore, the compressive strength of the modified material was measured in the same manner as described above. These results are shown in Table 8. As shown in Table 8, the longer the air-drying curing period of the primary mixture, the higher the compressive strength.

[0042] [Table 8]

Claims

1. A method for producing a modified expandable soil, comprising at least the following steps (A) to (D) and the subsequent divisional addition of the following expandable soil modifier to produce the modified expandable soil described below. (A) Per 100 parts by mass of expansive soil, of which 0 to 10 parts by mass of salt or seawater (in terms of salinity), 0 to 30 parts by mass of Portland cement, and 0 to 20 parts by mass of slaked lime, (A-1) An expansive soil modifier comprising at least one selected from seawater, Portland cement, and slaked lime. or, (A-2) Expanding soil modifier containing at least two ingredients selected from table salt and Portland cement or slaked lime. The process of preparing a primary mixture involves adding and mixing the ingredients to produce a primary mixture. (B) A process for producing a crushed primary mixture, in which the primary mixture is cured and then crushed to produce a crushed primary mixture. (C) A process for preparing a secondary mixture, in which an expandable soil modifier containing at least 0 to 30 parts by mass of Portland cement and 0 to 20 parts by mass of slaked lime per 100 parts by mass of expandable soil in the above-mentioned crushed material is added to the above-mentioned crushed material and mixed to prepare a secondary mixture. (D) Compaction process of the secondary mixture to obtain an expandable soil modified material by compacting the above secondary mixture.

2. Furthermore, the method for producing an expandable soil modifier according to claim 1, further comprising (A) a compaction step of compacting the primary mixture prepared in the primary mixture preparation step.

3. The method for producing a modified expansive soil according to claim 1, wherein the amount of the above-mentioned modifier added in stages is 0.01 to 20 parts by mass for primary addition and 1 to 20 parts by mass for secondary addition, per 100 parts by mass of expansive soil.

4. The method for producing an expandable soil modifier according to claim 1, wherein the curing period for the above-mentioned primary mixture is 7 days to 1 year.

5. A method for producing an expandable soil modification according to claim 1, wherein the particle size of the crushed material is 200 mm or less.

6. A method for producing an expandable soil modifier according to claim 1, wherein in the case of (a) below, water is added when the modifier is added for the first time, and in the case of (b) below, water is added when the modifier is added for the second time. (a) When the viscosity of the expansive soil is high, making it difficult or impossible to mix the modifier. (b) The compressive strength of the secondary mixture after the curing process is 0.5 N / mm² at the time of crushing. ２ In the above cases

7. A method for producing a modified expandable soil according to any one of claims 1 to 6, wherein the expandable soil is black cotton soil.

8. A method for modifying expandable soil, comprising at least the following steps (A) to (D), followed by the partial addition of the following expandable soil modifier. (A) Per 100 parts by mass of expansive soil, of which 0 to 10 parts by mass of salt or seawater (in terms of salinity), 0 to 30 parts by mass of Portland cement, and 0 to 20 parts by mass of slaked lime, (A-1) An expansive soil modifier comprising at least one selected from seawater, Portland cement, and slaked lime. or, (A-2) Expanding soil modifier containing at least two ingredients selected from table salt and Portland cement or slaked lime. The process of preparing a primary mixture involves adding and mixing the ingredients to produce a primary mixture. (B) A process for producing a crushed primary mixture, in which the primary mixture is cured and then crushed to produce a crushed primary mixture. (C) A process for preparing a secondary mixture, in which an expandable soil modifier containing at least 0 to 30 parts by mass of Portland cement and 0 to 20 parts by mass of slaked lime per 100 parts by mass of expandable soil in the above-mentioned crushed material is added to the above-mentioned crushed material and mixed to prepare a secondary mixture. (D) Compaction process of the secondary mixture to obtain an expandable soil modified material by compacting the above secondary mixture.

9. Furthermore, the method for modifying expansive soil according to claim 8, further comprising (A) a compaction step of compacting the primary mixture prepared in the primary mixture preparation step.

10. The method for modifying expansive soil according to claim 8, wherein the amount of the above-mentioned modifier added in stages is 0.01 to 20 parts by mass for primary addition and 1 to 20 parts by mass for secondary addition, per 100 parts by mass of expansive soil.

11. The method for modifying expansive soil according to claim 8, wherein the curing period for the primary mixture is 7 days to 1 year.

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