Mud material

Abstract

To provide a slurry-adding material capable of imparting plastic flowability to excavated sediment even if the content of bentonite is smaller than that of a conventional product.SOLUTION: The admixture contains a highly swellable bentonite, water glass, a salt and water, wherein the content of the highly swellable bentonite is less than 20 mass% based on 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 material or aerating material to harden the soil to a certain degree, generating pressure to counter 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, particularly one containing coarse gravel of 20 mm or more, the mud-adding material must be in a hard gel form to impart plastic fluidity to the excavated soil and sand. 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 additives, which are required to be in a hard 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 often confined spaces in 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] An object of the present invention is to provide a mud-adding material that contains less bentonite than conventional products and can impart plastic fluidity to excavated soil and sand. [Means for solving the problem]

[0007] One embodiment of the present invention is a mud-adding material containing highly swelling bentonite, water glass, salt, and water, in which the content of highly swelling bentonite is less than 20 mass % relative to the water.

[0008] Furthermore, it is preferable that the salt of the mud-adding material is a compound having a divalent cation. Furthermore, the content of highly swelling bentonite in the mud-adding material is preferably 12.50% by mass to 17.50% by mass relative to water. The mud-adding material preferably has a water glass content of 2.5% by mass to 10% by mass relative to the water. [Effects of the Invention]

[0009] According to the method of the present invention, it is possible to provide a mud-adding material that contains less bentonite than conventional products and is capable of imparting plastic fluidity to excavated soil and sand. DETAILED DESCRIPTION OF THE INVENTION

[0010] (Mud-added material) The mud-adding material according to this embodiment contains highly swelling bentonite, water glass, salt, and water, and further contains other components as required.

[0011] <Highly swelling bentonite> Bentonite is a clay mineral primarily composed of montmorillonite, which is composed of crystals with a structure in which cations exist between negatively charged layers. Bentonite that exhibits certain values ​​for swelling capacity is classified as highly swelling bentonite. Highly swelling bentonite is used as a material to adjust the viscosity and gelation degree of mud-adding materials. Here, the viscosity of the mud-adding material refers to the viscosity of bentonite mud water in which bentonite is dissolved in water or the viscosity of a bentonite solution in which bentonite is dissolved in water containing salt. The degree of gelation refers to whether the hardness of the gel is uniform throughout the gel.

[0012] In this embodiment, highly swelling bentonite refers to bentonite having a swelling amount of more than 10 mL / 2 g, or bentonite mud water containing 8% by mass of bentonite relative to water having a funnel viscosity of 21 seconds or more.

[0013] The swelling amount was measured based on the Bentonite Industry Association's standard test method (JBAS-104-77 "Test method for swelling of powdered bentonite"). Specifically, 2.0 g of bentonite sample was added to a 100 mL glass-stoppered measuring cylinder containing 100 mL of distilled water, and left to stand for 24 hours. The apparent volume of the swollen sample mass at the bottom of the measuring cylinder was read from the scale on the measuring cylinder.

[0014] The funnel viscosity is a value measured using a funnel viscometer (e.g., S-251, manufactured by Nishinippon Shikenki Co., Ltd.) for an 8% by mass bentonite muddy water to be measured. Specifically, the bentonite muddy water is collected into the collection container (500 mL) of the funnel viscometer until the top of the container is filled with the bentonite muddy water, the outlet at the bottom of the funnel viscometer is blocked with a finger, the collected bentonite muddy water is poured from the top of the funnel viscometer, the finger blocking the outlet at the bottom of the funnel viscometer is removed, and the time (in seconds) for the bentonite muddy water to flow out is measured with a stopwatch.

[0015] Bentonite is classified according to the type of cations present between the layers of montmorillonite crystals, and many bentonites that meet the above conditions (i.e., highly swelling bentonites) are sodium-type bentonites that have a large number of sodium ions among the cations present between the layers of montmorillonite. The highly swelling bentonite may be suitably synthesized or may be a commercially available product.

[0016] The content of the highly swelling bentonite relative to the amount of water is less than 20% by mass, preferably 12.50% to 17.50% by mass, more preferably 13.75% to 17.50% by mass, and even more preferably 13.75% to 15.00% by mass. If the content of the highly swelling bentonite is less than 20% by mass, the viscosity and degree of gelation become appropriate values ​​for a mud-adding agent, and as a result, the amount of bentonite can be reduced.

[0017] <Water glass> Water glass is contained to gel the mud-adding material. Water glass, also called sodium silicate or sodium silicate, is an aqueous solution of sodium silicate, specifically 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.

[0018] The content of water glass is not particularly limited and can be appropriately selected depending on the purpose, but is preferably 2.5 to 10 mass %, more preferably 2.5 to 5 mass %, based on the total amount of highly swelling bentonite, salt, and water (bentonite mud containing salt, hereinafter also referred to as "bentonite solution"). When the content of water glass is 2.5 to 10 mass %, plastic fluidity can be imparted to the excavated soil and sand.

[0019] <Salt> The salt is a compound consisting of an anion and a cation, and is contained to make the highly swelling bentonite more soluble in water. The type of salt is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include aluminum salts, magnesium salts, calcium salts, sodium salts, and sulfate salts. These may be used alone or in combination of two or more. Among these, compounds having a divalent cation are preferred in terms of reactivity with water glass, which will be described later. Specific examples of compounds having a divalent cation include magnesium salts and calcium salts. The anions for the magnesium salt and calcium salt are not particularly limited and can be appropriately selected depending on the purpose, but chlorides are preferred from the viewpoint of reactivity with water glass, which will be described later. Examples of chlorides of divalent cations include calcium chloride and magnesium chloride.

[0020] The salt content is not particularly limited and can be appropriately selected depending on the purpose, and is preferably 0.175 to 0.350 mass %, more preferably 0.200 to 0.350 mass %, and even more preferably 0.250 to 0.325 mass %, relative to water.

[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 salt is dissolved in water and highly swelling bentonite is dispersed in the water to produce a salt-containing bentonite mud (bentonite solution), and the bentonite solution and water glass are mixed just before being injected into the face and / or chamber to obtain the mud additive; or a method in which the bentonite solution and water glass solution are injected separately into the face and / or chamber, and then mixed to obtain the mud additive.

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

[0025] The bentonite used was as follows. The swelling amount of each bentonite and the funnel viscosity of 8 mass % bentonite mud water are shown in Table 1. Bentonite 1: Kunigel VA (Kunimine Industries Co., Ltd.) Bentonite 2: Kunibond TY (Kunimine Industries Co., Ltd.) Bentonite 3: Auxiliary Agent M (manufactured by Onoda Chemico Co., Ltd.)

[0026] <Funnel viscosity (FV) measurement> The funnel viscosity was measured using a funnel viscometer (S-251, manufactured by Nishinippon Shikenki Co., Ltd.) Specifically, the bentonite mud water was collected into the collection container (500 mL) of the funnel viscometer until it was full to the top, the outlet at the bottom of the funnel viscometer was blocked with a finger, the collected bentonite mud water was poured from the top of the funnel viscometer, the finger blocking the outlet at the bottom of the funnel viscometer was removed, and the time (in seconds) for the bentonite mud water to flow out was measured with a stopwatch to obtain the viscosity.

[0027] <Measurement of swelling amount> The swelling amount was measured based on the Bentonite Industry Association's standard test method (JBAS-104-77 "Test method for swelling of powdered bentonite"). Specifically, 2.0 g of bentonite sample was added to a 100 mL glass-stoppered measuring cylinder containing 100 mL of distilled water, and allowed to stand for 24 hours. After standing, the apparent volume of the swollen sample mass at the bottom of the measuring cylinder was read from the scale on the measuring cylinder, and the swelling amount (mL / 2 g) was measured.

[0028] [Table 1]

[0029] (Examples 1 to 8) <Making mud-adding materials> Each salt was dissolved in water to the concentration shown in Table 2, and then Bentonite 1 (highly swelling bentonite) was added to the water to give a concentration of 15% by mass to prepare a salt-containing bentonite mud solution (bentonite solution). Next, water glass (No. 3 sodium silicate, manufactured by Fuji Chemical Co., Ltd.) was added to the prepared bentonite solution in an amount of 5% by mass based on the bentonite solution to prepare a muddy material. The salt concentrations listed in Table 2 are the ratios to water (external ratios relative to 100% water).

[0030] <Evaluation of gel properties> The properties of the resulting muddy material as a gel were evaluated based on the following evaluation criteria. The evaluation results are shown in Table 2. -Evaluation criteria- ◎: The muddy material is hard (pudding-like) and takes less than 1 minute to gel. 〇: The mud material is hard (pudding-like) and takes more than 1 minute to gel △: The mud material is soft (yogurt-like) and takes more than 1 minute to gel.

[0031] [Table 2]

[0032] As shown in Table 2, the mud-adding materials of Examples 1 to 8 became gels with sufficient hardness to be used as mud-adding materials. From these results, it can be said that even if the type of salt is changed, plastic fluidity can be imparted to the excavated soil and sand.

[0033] Furthermore, magnesium salts and calcium salts (Examples 1 to 3, 6 to 8), which are compounds having divalent cations, form harder gels than aluminum salts (Examples 4 and 5), which are compounds having trivalent cations, so it can be said that salts made of compounds having divalent cations are preferable. Furthermore, when comparing magnesium salts with calcium salts, calcium salts can form a gel in a shorter time, and therefore calcium salts are more preferable.

[0034] (Examples 9 to 26, Comparative Examples 1 and 2) <Making mud-adding materials> Each salt was dissolved in water to the concentration shown in Table 3, and then high-swelling bentonite was mixed in Examples 9 to 26 to prepare salt-containing bentonite mud (bentonite solution). For Comparative Examples 1 and 2, low-swelling bentonite was mixed in water to prepare bentonite mud. The funnel viscosity (FV) of the prepared bentonite solution or bentonite mud was measured using the method described above. The measurement results are shown in Table 3. If the funnel viscosity of the bentonite solution exceeds 60 seconds, it becomes difficult to pump the mud-adding material. The concentrations of salt and bentonite shown in Table 3 are in mass % (exclusive ratio relative to 100% water).

[0035] Next, water glass (No. 3 sodium silicate, manufactured by Fuji Chemical Co., Ltd.) was added to the obtained bentonite solution or bentonite mud solution to a concentration shown in Table 3, and mixed to obtain a mud-adding agent. The concentrations of water glass shown in Table 3 are the percentages (mass %) of the mass of the bentonite solution or bentonite muddy water.

[0036] <Cylinder flow (SF) test> A cylinder flow (SF) test was conducted on the resulting mud-added material. The test was conducted in accordance with the cylinder method of the consistency test method in the Japan Highway Public Corporation standard "Test Method for Air Mortar and Painted Mortar (JHS A 3113-1992)." Specifically, a cylinder with an inner diameter of 80 mm and a height of 80 mm was placed on a 450 mm side flow plate installed on a flat surface. The cylinder was filled with the mud-added material so that no voids were formed, the top surface was leveled, and the cylinder was gently lifted vertically upward. The maximum diameter of the expanded mud-added material and the diameter perpendicular to that diameter were then measured, and the average of these was taken as the flow value. The test results are shown in Table 3.

[0037] [Table 3]

[0038] The funnel viscosity of the bentonite solution in the mud-adding materials of Examples 9 to 26 was less than 60 seconds, and the cylinder flow measurement results for the mud-adding materials were less than 125 mm. This tendency was also observed in Comparative Example 1, which contained 20 mass% of low-swelling bentonite alone. Furthermore, in Comparative Example 2, which contained 16 mass% of low-swelling bentonite alone, the funnel viscosity of the bentonite mud was 20.6 seconds, and the cylinder flow measurement result was 167 mm. The results of Comparative Examples 1 and 2 clearly show that using only low-swelling bentonite cannot impart plastic fluidity to the excavated soil and sand if the amount of bentonite is reduced. From the above, it can be said that the mud-adding materials of Examples 9 to 26 can impart plastic fluidity to the excavated soil and sand even though the bentonite concentration is lower than that of conventional products.

[0039] <Evaluation of adding muddy materials to soil> The mud-adding material was added to the simulated soil and evaluated. The simulated soil used was one with the following conditions: <<Conditions of the simulated soil>> Fine particle content (silt / clay): 5.4% (fine particles are defined as particles less than 0.075 mm) Sand content: 21.6% (sand is defined as particles between 0.075mm and 2mm) Gravel content: 73% (gravel is defined as particles 2mm or larger)

[0040] (Examples 27 to 31, Comparative Example 3) After adding 5% by mass of water to the simulated soil, 20% by volume of bentonite solution or bentonite muddy water with the concentrations shown in Table 4 was added to the simulated soil volume, and water glass was added in an amount to achieve the concentrations shown in Table 4, followed by mixing and stirring to prepare soil samples containing muddy materials. The obtained samples were evaluated by the table flow test (TF) and mini-slump test (MSL) as described below. The evaluation results are shown in Table 4. If the table flow test result of the obtained sample is 130mm or less and the mini-slump test result is 4.0cm or less, the mud-adding material can impart plastic fluidity to the excavated soil. Furthermore, if the funnel viscosity of the bentonite solution in the mud-adding material is less than 60 seconds and the cylinder flow of the mud-adding material is less than 125mm, when mixed with simulated soil, the table flow test result will be 130mm or less and the mini-slump test result will be 4.0cm or less.

[0041] <Table Flow Test (TF)> The table flow test was conducted in accordance with JIS R 5201:2015 "Physical Testing Methods for Cement," Section 12, Flow Test. Specifically, the sample was packed into a flow cone (top inner diameter 70±0.5 mm, bottom inner diameter 100±0.5 mm, height 60±0.5 mm) in two layers, and each layer was tamped 15 times over the entire surface. Finally, additional filling was added as necessary to smooth the surface. The flow cone was then gently removed vertically and allowed to fall 15 times over a 15-second period. The diameter of the sample after spreading was measured to the nearest 1 mm in the direction recognized as the largest and in the direction perpendicular to that direction, and the average of these measurements was taken as the table flow value (mm).

[0042] <Mini-Slump Test (MSL)> The mini-slump test was conducted in accordance with JIS A 1171:2016 "Test Methods for Polymer-Cement Mortar," Section 6.2, "Fresh Polymer-Cement Mortar Flow Test." Specifically, a slump cone (top inner diameter 50±0.5 mm, bottom inner diameter 100±0.5 mm, height 150±0.5 mm) was placed on a horizontally placed steel plate, and the sample was packed into two layers of approximately equal volume. Each layer was leveled with a ram. The top of the slump cone was then leveled and gently pulled vertically. The drop in the center of the sample was measured to the nearest 1 mm, and this was recorded as the mini-slump test measurement value (cm).

[0043] [Table 4]

[0044] As is clear from Table 4, for Examples 27 to 31, the table flow test was 130 mm or less, and the mini-slump test was 4.0 cm or less. This result is similar to that of Comparative Example 3, which contains a relatively large amount of bentonite. Therefore, the mud-adding materials of Examples 27 to 31 can impart plastic fluidity to the excavated soil and sand, even though they contain less bentonite than conventional products.

Claims

1. Contains high swelling bentonite, water glass, salt, and water, A mud-adding material characterized in that the content of the highly swelling bentonite is less than 20 mass% relative to the water.

2. The mud-adding material according to claim 1, wherein the salt is a compound having a divalent cation.

3. The mud-adding material according to claim 1 or 2, wherein the content of the highly swelling bentonite is 12.50% by mass to 17.50% by mass relative to the water.

4. The mud-adding material according to claim 1 or 2, wherein the content of the water glass is 2.5% by mass to 10% by mass relative to the water.

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