Mud-added material

Abstract

To provide a mud-added material that enables the impartation of plastic flowability to excavated soil, even when the bentonite content is lower than that of conventional products.SOLUTION: A mud-added material comprising high-swelling bentonite, low-swelling bentonite, water glass, and water, wherein the total content of high-swelling and low-swelling bentonite is less than 20 mass% relative to the amount of water.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a mud-adding material. [Background technology]

[0002] The mud pressure shield method is a construction method in which the soil excavated by a shield excavator is mixed with a mud-adding or aerating material to harden the soil to a certain degree, generating pressure that counteracts the groundwater pressure and earth pressure acting on the face of the shield excavator, thereby stabilizing the face and promoting excavation.

[0003] Many mud-adding materials are primarily made of bentonite with appropriate additives added (see, for example, Patent Document 1). However, when the excavation target is gravelly ground, especially when it contains coarse gravel of 20 mm or more, the mud-adding material must be in a strong gel form to give the excavated soil and sand plastic fluidity. In such cases, a mud-adding material made by mixing bentonite with water glass is often used. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-6999 Summary of the Invention [Problem to be solved by the invention]

[0005] Generally, mud-adding materials, which are required to be in a gel state, need to contain a relatively high amount of bentonite, at least 20% by mass relative to the water. However, shield tunneling construction sites are generally located in narrow urban areas where it is difficult to secure storage space for large amounts of bentonite. This means that bentonite needs to be transported frequently, which poses productivity problems. On the other hand, if the bentonite content is reduced, it becomes more difficult to give plastic fluidity to the excavated soil.

[0006] The object of the present invention is to provide a mud additive that can impart plastic fluidity to excavated earth and sand with at least less bentonite content than conventional products.

Means for Solving the Problems

[0007] One embodiment of the present invention is a mud additive containing highly swelling bentonite, low swelling bentonite, water glass, and water, wherein the total content of highly swelling bentonite and low swelling bentonite is less than 20% by mass with respect to water. Moreover, it is preferable that the content of highly swelling bentonite in the mud additive is 4% to 7% by mass with respect to water. Moreover, it is preferable that the content of low swelling bentonite in the mud additive is 6% to 15% by mass with respect to water. Moreover, it is preferable that the content of water glass in the mud additive is 2.5% to 10% by mass with respect to water.

Effects of the Invention

[0008] According to the method of the present invention, it is possible to provide a mud additive that can impart plastic fluidity to excavated earth and sand with at least less bentonite content than conventional products.

Modes for Carrying Out the Invention

[0009] (Mud Additive) The mud additive according to the present embodiment contains highly swelling bentonite, low swelling bentonite, water glass, and water, and further contains other components as necessary.

[0010] Bentonite is a clay mineral mainly composed of montmorillonite, which has a structure in which cations exist between negatively charged layers. It is classified into highly swelling bentonite and low swelling bentonite according to the swelling amount and the like as follows. In the mud additive according to the embodiment, highly swelling bentonite and low swelling bentonite ​The total content is less than 20% by mass with respect to water.

[0011] <High-swelling bentonite> High-swelling bentonite is used as a material for adjusting the viscosity of the mud material and the degree of gelation of the mud material. Here, the viscosity of the mud material refers to the viscosity of the bentonite solution, and the degree of gelation refers to whether it has uniformly gelled.

[0012] In this embodiment, high-swelling bentonite refers to bentonite having a swelling amount greater than 10 mL / 2 g or a funnel viscosity of a 8% by mass solution of 21 seconds or more. The swelling amount is a value measured based on the Standard Test Method of the Bentonite Industry Association (JBAS-104-77 "Swelling Test Method for Bentonite (Powdery)"). Specifically, it is a value obtained by adding 2.0 g of a bentonite sample to a 100 mL stoppered graduated cylinder containing 100 mL of distilled water, allowing it to stand for 24 hours, and reading the apparent volume of the swollen sample mass at the bottom of the graduated cylinder from the scale of the graduated cylinder.

[0013] The funnel viscosity is a value measured using a funnel viscometer (for example, S-251, manufactured by Nippon Test Machine Co., Ltd.) for an 8% by mass solution of the bentonite to be measured. Specifically, it is a value obtained by collecting the bentonite solution to the brim of the mouth with the sampling container (500 mL) of the funnel viscometer, covering the outlet at the bottom of the funnel viscometer body with a finger, pouring all the collected bentonite solution from above the funnel viscometer body, then removing the finger covering the outlet at the bottom of the funnel viscometer, and measuring the time (in seconds) for the bentonite solution to flow out with a stopwatch.

[0014] Bentonite is classified according to the type of cation present between the crystal layers of montmorillonite. Among bentonites that satisfy the above conditions, there are many sodium-type bentonites having a large amount of sodium ions among the cations present between the layers of montmorillonite. High-swelling bentonite may be appropriately synthesized or a commercially available product may be used.

[0015] The content of the highly swelling bentonite is not particularly limited and can be appropriately selected according to the purpose. However, with respect to water, 4% to 7% by mass is preferable, 5% to 7% by mass is more preferable, and 6% to 7% by mass is even more preferable. When the content of the highly swelling bentonite is 4% to 7% by mass, the viscosity and the degree of gelation become appropriate values as the mud-added material, and as a result, the amount of bentonite can be reduced.

[0016] <Low-swelling bentonite> Low-swelling bentonite is used as a material for adjusting the gel strength. In the present embodiment, the low-swelling bentonite refers to bentonite having a swelling amount of 10 mL / 2 g or less, or a funnel viscosity of a solution of 8% by mass of less than 21 seconds. The measuring methods of the swelling amount and the funnel viscosity are the same as the above-described methods.

[0017] Among bentonites satisfying the above conditions, there are many calcium-type bentonites having a large amount of calcium ions in the cations existing between the layers of montmorillonite. The low-swelling bentonite may be appropriately synthesized or a commercially available product may be used.

[0018] The content of the low-swelling bentonite is not particularly limited and can be appropriately selected according to the purpose. However, with respect to water, 6% to 15% by mass is preferable, 6% to 14% by mass is more preferable, and 7% to 12% by mass is even more preferable. When the content of the low-swelling bentonite is 6% to 15% by mass, the gel strength of the mud-added material becomes an appropriate value, and as a result, plastic fluidity can be imparted to the excavated earth and sand.

[0019] <Water glass> Water glass is contained in order to gel the mud-added material. Water glass is also called sodium silicate or sodium metasilicate, and is an aqueous solution of sodium silicate. Specifically, it is a mixture of silicon dioxide, sodium oxide, and water. Water glass is classified according to the ratio of silicon dioxide to silicon oxide, from No. 1, which has the highest silicon dioxide content, to No. 5, which has the lowest. The ratio in this case is by weight. The mud-adding material in the embodiment is not particularly limited and can be appropriately selected depending on the purpose. One type of water glass may be used, or two or more types may be used in combination.

[0020] The content of water glass is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 2.5% by mass to 10% by mass relative to the water. When the content of water glass is 2.5% by mass to 10% by mass, plastic fluidity can be imparted to the excavated soil and sand.

[0021] <Water> The water is not particularly limited and can be appropriately selected depending on the purpose. Examples include tap water and distilled water. The water content is not particularly limited and can be appropriately selected depending on the purpose.

[0022] <Other ingredients> The other components are not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include clay minerals other than bentonite. The content of other components is not particularly limited as long as it does not impair the performance of the mud-adding material, and can be selected appropriately depending on the purpose.

[0023] <Method of manufacturing muddy materials> There are no particular restrictions on the method for producing the mud additive, and it can be selected appropriately depending on the purpose. For example, there is a method in which a bentonite solution in which bentonite is dispersed in water is mixed with water glass just before being injected into the face and / or chamber to obtain the mud additive, and a method in which a bentonite solution and a water glass solution are injected separately into the face and / or chamber and then mixed to obtain the mud additive.

[0024] Examples of the disclosed technology will be described below, but the disclosed technology is not limited to these examples.

[0025] (Examples 1 to 17, Comparative Examples 1 to 4) Bentonite was used as described below. The swelling amount of each bentonite and the funnel viscosity of the 8 mass% bentonite solution are shown in Table 1. · Highly swelling bentonite 1: Kunigel VA (manufactured by Kunimine Industries Co., Ltd.) · Highly swelling bentonite 2: Kunibond TY (manufactured by Kunimine Industries Co., Ltd.) · Low swelling bentonite 1: Kunibond C (manufactured by Kunimine Industries Co., Ltd.) · Low swelling bentonite 2: Auxiliary agent M (manufactured by Onoda Chemical Co., Ltd.)

[0026] <Measurement of funnel viscosity (FV)> The funnel viscosity was measured using a funnel viscometer (S-251, manufactured by Nippon Test Machine Co., Ltd.). Specifically, the bentonite solution was collected to the brim of the mouth with the sampling container (500 mL) of the funnel viscometer, the outlet at the bottom of the funnel viscometer body was blocked with a finger, and after pouring all the collected bentonite solution from above the funnel viscometer body, the finger blocking the outlet at the bottom of the funnel viscometer was released, and the time (in seconds) for the bentonite solution to flow out was measured with a stopwatch.

[0027] <Measurement of swelling amount> The swelling amount was measured based on the Standard Test Method of the Bentonite Industry Association (JBAS-104-77 "Swelling Test Method for Bentonite (Powdery)"). Specifically, 2.0 g of the bentonite sample was added to a 100 mL stoppered graduated cylinder containing 100 mL of distilled water and allowed to stand for 24 hours. After standing, the apparent volume of the sample mass at the bottom of the graduated cylinder that had swelled was read from the scale of the graduated cylinder, and the swelling amount (mL / 2 g) was measured.

[0028]

Table 1

[0029] <Preparation of sludge additive> The highly swelling bentonite and the low swelling bentonite were mixed in water so as to have the concentrations shown in Table 2, and a bentonite solution was prepared. The funnel viscosity of the prepared bentonite solution was measured by the method described above. The measurement results are shown in Table 3. When the funnel viscosity of the bentonite solution exceeds 60 seconds, it becomes difficult to pump and transport the slurry material. The numerical values shown in Table 2 are ratios (mass %) with respect to water.

[0030] Next, water glass (sodium silicate No. 3, manufactured by Fuji Chemical Co., Ltd.) was added to the obtained bentonite solution so as to have the concentrations shown in Table 2, and they were mixed to obtain a slurry material.

[0031]

Table 2

[0032] The cylinder flow test of the obtained slurry material was carried out according to the following procedure. The measurement results are shown in Table 3. When the measurement result of the cylinder flow exceeds 125 mm, it becomes difficult to collect the excavated earth and sand.

[0033] <Measurement of Cylinder Flow> The cylinder flow was carried out in accordance with the cylinder method of the consistency test method of the Japan Road Association Standard "Test Methods for Air Mortar and Picture Milk (JHS A 3113-1992)". Specifically, a cylinder with an inner diameter of 80 mm and a height of 80 mm was placed on a flow plate with a side length of 450 mm installed on a flat place, the cylinder was filled with the slurry material so that no voids were generated, the upper end surface was leveled, and the cylinder was gently pulled vertically upward. Then, the diameter recognized as the maximum of the spread slurry material and the diameter in the direction perpendicular to the said diameter were measured, and the average of these was taken as the flow value.

[0034]

Table 3

[0035] For the mud additives of Examples 1 to 17, similar to Comparative Example 1, the funnel viscosity was less than 60 seconds and the cylinder flow was less than 125 mm. In contrast, for Comparative Example 2 containing less than 20% by mass of only low-swelling bentonite, the cylinder flow was 167 mm. Also, for Comparative Examples 3 and 4 containing 10% by mass of only high-swelling bentonite, the funnel viscosity was 60 seconds or more. From the above, it can be said that the mud additives of Examples 1 to 17 can impart plastic fluidity to the excavated earth and sand even when the bentonite concentration is less than that of conventional products.

[0036] <Evaluation when the mud additive is added to the soil> Regarding the mud additives of Examples 15 and 16 and Comparative Example 1, an evaluation was conducted when added to the simulated soil. As the simulated soil, a simulated soil under the following conditions was used. <<Conditions of the simulated soil>> · Fine particle content (silt + clay content) 5.4% (fine particles are particles less than 0.075 mm) · Sand content 21.6% (sand is particles of 0.075 mm or more and less than 2 mm) · Gravel content 73% (gravel is particles of 2 mm or more)

[0037] After adding 5% by mass of water to the simulated soil, a bentonite solution with the concentration shown in Table 2 was added at 20% by volume per volume of the simulated soil, water glass was added, and the mixture was stirred to prepare a sample. For the obtained sample, a table flow test (TF) and a mini slump test (MSL) were conducted and evaluated as follows. The evaluation results are shown in Table 4. When the table flow test is 130 mm or less and the mini slump test is 4.0 cm or less, when used as a mud additive, plastic fluidity can be imparted to the excavated earth and sand. Note that when the funnel viscosity of the bentonite solution contained in the mud additive is less than 60 seconds and the cylinder flow of the mud additive is less than 125 mm, the table flow test when mixed with the simulated soil is 130 mm or less and the mini slump test result is 4.0 cm or less.

[0038] <Table flow test (TF)> The table flow test was conducted in accordance with the 12-flow test of JIS R 5201:2015 "Methods of Physical Testing for Cement". Specifically, the sample was packed in two layers into a flow cone (upper inner diameter 70 ± 0.5 mm, lower inner diameter 100 ± 0.5 mm, height 60 ± 0.5 mm), and each layer was tamped 15 times over the entire surface. Finally, if necessary, the insufficient amount was added, etc., to level the surface. Then, the flow cone was gently removed vertically upward, and a dropping motion of 15 times in 15 seconds was applied. The diameter after the sample spread was measured to the nearest 1 mm in the direction where the maximum was recognized and in the direction perpendicular to this, and their average was taken as the table flow value (mm).

[0039] <Mini Slump Test (MSL)> The mini slump test was conducted in accordance with the 6 fresh polymer cement mortar 6.2 flow test of JIS A 1171:2016 "Test Methods for Polymer Cement Mortar". Specifically, a slump cone (upper end inner diameter 50 ± 0.5 mm, lower end inner diameter 100 ± 0.5 mm, height 150 ± 0.5 mm) was placed on a steel flat plate installed horizontally, and the sample was packed in two layers of approximately equal amounts. Each layer was leveled with a tamping rod. Then, the upper end of the slump cone was leveled and gently pulled up vertically, and the drop of the central part of the sample was measured in 1-mm units and taken as the measured value (cm) of the mini slump test.

[0040]

Table 4

[0041] As is clear from Table 4, for Examples 15 and 16, the table flow test is 130 mm or less, and the mini slump test is 4.0 cm or less. Therefore, the admixtures of Examples 15 and 16 can impart plastic fluidity to the excavated soil and sand even with less bentonite than the conventional products.

Claims

1. Containing highly swelling bentonite, low swelling bentonite, water glass, and water, The admixture is characterized in that the total content of the highly swelling bentonite and the low swelling bentonite is less than 20% by mass with respect to the water.

2. The admixture according to claim 1, wherein the content of the highly swelling bentonite is 4% to 7% by mass with respect to the water.

3. The admixture according to claim 1 or 2, wherein the content of the low swelling bentonite is 6% to 15% by mass with respect to the water.

4. The admixture according to claim 1 or 2, wherein the content of the water glass is 2.5% to 10% by mass with respect to the water.

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