Mud additive, fiber for mud additive, and shield method using the same

Abstract

To provide a mud additive and a fiber for mud additive, enabling excavated soil to have plastic fluidity, and a shield method using the same.SOLUTION: A mud additive comprises: a clay mineral: and a fiber that is at least one selected from regenerated cellulose fiber, semi-synthetic fiber, and synthetic fiber and that has an aspect ratio of 100 to 1,450.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a mud-adding material, a fiber for the mud-adding material, and a shield construction method using the same. [Background technology]

[0002] The earth pressure shield method involves mixing the soil and sand obtained by excavating the ground with mud-adding materials inside a shield machine to convert it into mud with plastic fluidity (irreversible deformation that occurs in materials subjected to stress beyond a certain limit), and using the resulting mud to adjust the pressure applied to the shield machine's cutters.

[0003] Examples of mud-adding materials that have been proposed so far include a copolymer of acrylamide and sodium acrylate (e.g., Patent Document 1) and an oil-in-water emulsion obtained by dispersing an acrylic acid polymer in water (e.g., Patent Document 2).

[0004] The components of the mud-adding material vary depending on the properties of the ground being excavated, but when excavating ground that is rich in gravel with little fine grain content, it has been proposed to mix in clay minerals such as bentonite and fine fibrous material (see, for example, Patent Document 3).

[0005] It has also been proposed to use cellulose fibers as a mud-adding agent for mud with a high moisture content (mud with a high water content). Examples of cellulose fibers include chemical pulps such as LBKP and NBKP, fibers derived from wood pulp such as mechanical pulps such as GP, RMP, TMP, fibers derived from non-wood raw materials such as kenaf, bagasse, bamboo, hemp, cotton, rice straw, rice husks, and natural cellulose fibers such as waste paper and other cellulosic waste that have been made into a fibrous form, or fibers that have been subjected to various treatments such as mercerization, liquid ammonia treatment, and fluff machine treatment, and various wood chips that have been defibrated (see, for example, Patent Document 4). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2020-117887 A [Patent Document 2] JP 2003-155475 A [Patent Document 3] Japanese Patent Application Publication No. 4-136397 [Patent Document 4] JP 2013-163776 A Summary of the Invention [Problem to be solved by the invention]

[0007] When the mud pressure shield method is applied to a ground with a high gravel content and the resulting soil is turned into mud using conventional mud-adding materials, the gravel cannot be consolidated and remains separated into small pieces, making it difficult to give it plastic fluidity.

[0008] To deal with this situation, a method of adding a compound that improves the viscosity of the composition, such as a gelling agent, to the mud-adding material is considered. However, a composition with improved viscosity can cause adhesion to the chamber and cutter in the shield machine and cause blockages. Furthermore, mixing a gelling agent to improve the viscosity of the soil requires the use of a large amount of the gelling agent.

[0009] The present invention aims to provide a mud-adding material and a fiber for the mud-adding material that can impart plastic fluidity to excavated soil and sand, and a shield construction method using the same. [Means for solving the problem]

[0010] In order to achieve the above object, the present invention provides Clay minerals and At least one fiber selected from regenerated cellulose fibers, semi-synthetic fibers, and synthetic fibers, the fiber having an aspect ratio of 100 to 1,450; It is a mud-adding material containing In addition, in the mud-adding material of the present invention, the synthetic fiber is preferably at least one selected from polyolefin-based fibers and biodegradable fibers. In addition, in the mud-adding material of the present invention, it is preferable that the regenerated cellulose fiber is a viscose rayon fiber, the polyolefin fiber is a polypropylene fiber, and the biodegradable fiber is at least one selected from polylactic acid fiber and polylactic acid / polybutylene succinate composite fiber. In addition, in the mud-adding material of the present invention, the clay mineral is preferably a swelling clay mineral. In the mud-adding material of the present invention, the swelling clay mineral is preferably montmorillonite. In addition, the mud-adding material of the present invention is preferably bentonite, the swelling clay mineral of which is mainly composed of montmorillonite. Moreover, in the mud-adding material of the present invention, the fiber diameter of the fibers is preferably 0.006 mm to 0.1 mm. Moreover, the mud-adding material of the present invention preferably has a fiber content (dry weight %) of 0.18% to 3.3% relative to the clay mineral. In addition, in the shield tunneling method according to another aspect of the present invention, it is preferable to add the above-mentioned mud-adding material. Moreover, the fiber for a mud adding material according to another embodiment of the present invention is at least one selected from regenerated cellulose fiber, semi-synthetic fiber, and synthetic fiber, and has an aspect ratio of 100 to 1,450. Effect of the Invention

[0011] According to the present invention, it is possible to provide a mud-adding material and a fiber for the mud-adding material that can impart plastic fluidity to excavated soil and sand, as well as a shield construction method using the same. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram of a cross-section of a fiber having a non-circular cross-section. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] (Mud-adding materials, fibers for mud-adding materials) The mud-adding material according to the embodiment contains clay minerals and fibers, and further contains other components as necessary.

[0014] <Clay minerals> Clay minerals are fine-grained deposits found in the earth's strata. Clay minerals can be classified according to their properties. For example, there are swelling clay minerals that have the property of absorbing water and expanding.

[0015] The swelling clay minerals are minerals called smectites, and examples thereof include montmorillonite, beidellite, nontronite, saponite, hectorite, sauconite, and stevensite. These may be used alone or in combination of two or more. Among these, montmorillonite is preferred.

[0016] Clay minerals often exist as a mixture. One of them is bentonite, which is a mixture of montmorillonite. In the embodiment, it is preferable to use bentonite.

[0017] <<Bentonite>> Bentonite is a clay mineral whose main component is montmorillonite. Montmorillonite is composed of crystals with a structure in which cations exist between the negatively charged layers. Bentonite is classified according to the type of cations present between the layers of the montmorillonite crystals.

[0018] Sodium bentonite, which has many sodium ions among the cations present between the layers of montmorillonite, has high swelling properties and generally has a swelling power of 15 ml / 2 g to 30 ml / 2 g (high swelling properties). On the other hand, calcium-type bentonite, which has a large number of calcium ions among the cations present between the layers of montmorillonite, has a lower swelling property than sodium-type bentonite, and generally has a swelling power of 5 ml / 2 g to 8 ml / 2 g (low swelling). In addition to sodium-type and calcium-type bentonite, there is also activated bentonite (Na-exchanged bentonite). This is bentonite that has been artificially converted to sodium-type by adding sodium carbonate (Na2CO3) to calcium-type bentonite in order to improve the swelling property, which is the greatest feature of bentonite. Activated bentonite (Na-exchanged bentonite) has a much improved swelling degree than calcium-type bentonite, and generally has a swelling power of 15ml / 2g to 25ml / 2g.

[0019] The bentonite used in the mud-adding material according to the embodiment may be any of sodium type, calcium type, and activated (Na-exchanged) bentonite, or a mixture thereof. Bentonite may be either a synthetic product or a commercially available product.

[0020] <Textile> The fiber is at least one selected from regenerated cellulose fibers, semi-synthetic fibers, and synthetic fibers. This fiber is a mud-adding material. Regenerated cellulose fibers, semi-synthetic fibers, and synthetic fibers can be adjusted in fiber diameter, fiber length, and aspect ratio during the manufacturing process, so that fibers suitable for the excavated soil can be produced. Therefore, they are preferable in that they can impart plastic fluidity to the excavated soil. In the case of fibers that are difficult to adjust, such as natural fibers, in which fibers with different fiber diameters, fiber lengths, and aspect ratios are mixed, it is difficult to obtain stable plastic fluidity. In addition, natural fibers require a defibration process, but it is difficult to perform the defibration process on-site, and there is a disadvantage that the transportation cost is high when obtaining fibers that have been defibrated. In addition, regenerated cellulose fibers and synthetic fibers that are biodegradable are preferable in that they can be treated in an environmentally friendly manner without removing the fibers from the excavated soil.

[0021] Regenerated cellulose fibers are preferred because they have excellent water absorption, good affinity between the fiber surface and water, and good dispersibility in mud. In addition, regenerated cellulose fibers are biodegradable, allowing for environmentally friendly disposal. Examples of regenerated cellulose fibers include viscose rayon, cupra, solvent spun cellulose, polynosic, etc. The regenerated cellulose fibers may be used alone or in combination of two or more. Among these, viscose rayon (viscose rayon fiber) is preferred for the following reasons. Viscose rayon fiber is preferred because it has a low degree of molecular polymerization and orientation among regenerated cellulose fibers, making it flexible and easy to absorb water into the fiber (water absorption and swelling). Its high affinity with water makes it easy for the fiber to disperse uniformly with mud and clay minerals (especially bentonite), and the flexibility of the fiber allows it to have appropriate plastic fluidity. Moreover, viscose rayon fibers do not have a circular cross section, but rather have a chrysanthemum-like cross section with fine irregularities on the outer edge. These irregularities make it easier for the fibers to become entangled with mud and clay minerals (especially bentonite), and the fibers are more likely to disperse uniformly in the mud, which is preferable. The mechanism by which these fine irregularities are formed is thought to be as follows: The viscose extruded from the die hole immediately solidifies to form a surface layer (also called the skin layer), through which the viscose is dehydrated, and the inside is solidified and regenerated until it hardens. During this process, shrinkage occurs, and it is thought that the fine irregularities are formed as the volume decreases.

[0022] An example of the semi-synthetic fiber is acetate fiber. Although acetate fiber does not reach the regenerated cellulose fiber, it has a standard moisture regain of 3% to 7% and has a moderate water absorption and swelling property, and furthermore, the fiber cross section has a multi-lobed cross section. Since acetate fiber has an affinity with water due to its multi-lobed cross section, it is easy to disperse uniformly with mud and clay minerals (especially bentonite), and can have plastic fluidity. In addition, since acetate fiber has a multi-lobed cross section, the fiber surface is uneven, which makes it easy to entangle with mud and clay minerals (especially bentonite), and the fiber is easy to disperse uniformly in mud.

[0023] Synthetic fibers are fibers made from thermoplastic resins. Synthetic fibers have a lower specific gravity than regenerated cellulose fibers and can obtain plastic flowability with a small amount of addition. In addition, synthetic fibers have a higher fiber strength than regenerated cellulose fibers and can retain their shape when integrated with gravel in mud. From these points of view, synthetic fibers are preferred.

[0024] The thermoplastic resin is not particularly limited and can be appropriately selected depending on the purpose. Examples of the thermoplastic resin include polyester resins such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polytrimethylene terephthalate (PTT), polyethylene naphthalate (PEN), polylactic acid (PLA), polybutylene succinate (PBS), polyhydroxyalkanoate (PHA), polycaprolactone (PCL) and copolymers thereof; polypropylene, polyethylene (including high density polyethylene, low density polyethylene, linear low density polyethylene, etc.), polybutene-1, and propylene-based resins having propylene as the main component. Examples of the resin include at least one selected from the group consisting of polyolefin resins such as propylene copolymers (including propylene-ethylene copolymers and propylene-butene-1-ethylene copolymers), ethylene-vinyl alcohol copolymers, and ethylene-vinyl acetate copolymers; polyamide resins such as nylon 6, nylon 12, and nylon 66; acrylic resins containing acrylonitrile as a constituent component; polyvinyl alcohol resins; polyurethane resins; engineering plastics such as polycarbonate, polyacetal, polystyrene, and cyclic polyolefins, and elastomers thereof. These may be used alone or in combination of two or more.

[0025] Among synthetic fibers, polyolefin fibers are preferred because of their low specific gravity. Among the polyolefin fibers, polypropylene fibers are preferred. Among the polyolefin fibers, polypropylene fibers are preferred because they have a low specific gravity and can provide plastic flowability with a small amount added. Among synthetic fibers, biodegradable fibers are preferred because they can be disposed of in an environmentally friendly manner.

[0026] The biodegradable fiber is a fiber formed from a biodegradable resin. The biodegradable fiber is preferable in that it can be disposed of in an environmentally friendly manner without having to remove the fiber from the excavated soil and sand. Among the above-mentioned thermoplastic resins, examples of biodegradable resins include polylactic acid (PLA), polybutylene succinate (PBS), marine biodegradable polyhydroxyalkanoate (PHA), polycaprolactone (PCL), and the like. The biodegradable fiber may be a composite fiber. A composite fiber is a fiber produced by thermally melting two or more resins with different properties, compounding them when extruding them from a die, and spinning them. An example of a composite fiber of a biodegradable fiber is a polylactic acid / polybutylene succinate composite fiber (a composite fiber of polylactic acid and polybutylene succinate).

[0027] The synthetic fibers may be those whose surfaces have been treated with a fiber treatment agent. The fiber treatment agent is preferably an anionic surfactant, and examples of the anionic surfactant include metal carboxylates, metal sulfonates, and metal phosphates. It is believed that by treating the surface of synthetic fibers with an anionic surfactant, the surfactant on the surface of the synthetic fibers is more likely to react with clay minerals in the mud, especially metal salts such as bentonite, to become Ca salts or Na salts, which capture the bentonite particles, thereby improving dispersibility. Among the anionic fiber treating agents, alkyl phosphate alkali metal salts are preferred.

[0028] In addition to the above-mentioned fibers, natural fibers such as cotton may also be included to the extent that they do not affect the effects of the present invention.

[0029] The aspect ratio of the fibers (fiber length / fiber diameter) is from 100 to 1,450, preferably from 100 to 1,350, more preferably from 125 to 1,275, and further preferably from 150 to 1,150. Within the range of the aspect ratio, when synthetic fibers are used, the range is preferably 100 to 1,350, more preferably 130 to 1,150, and even more preferably 160 to 900. If the aspect ratio of the fibers is less than 100, the fibers will not be entangled well, and when the mud adding material is mixed with the excavated soil and sand, the mud adding material and the soil may not hold together. If the aspect ratio of the fibers is more than 1,450, the fibers will be entangled too well, and fibrous lumps (so-called fiber balls) will form in the mud adding material, and when the mud adding material is mixed with the excavated soil and sand, the mud adding material and the soil may not mix evenly.

[0030] The diameter of the fibers (fiber diameter) is not particularly limited and can be appropriately selected depending on the purpose, but from the viewpoint of ease of dispersion in mud and clay minerals, it is preferably 0.006 mm to 0.1 mm, more preferably 0.007 mm to 0.075 mm, and even more preferably 0.010 mm to 0.055 mm. When regenerated cellulose fibers are used, the fiber diameter is preferably 0.006 mm to 0.1 mm, more preferably 0.007 mm to 0.075 mm, and even more preferably 0.010 mm to 0.055 mm. Among the above fiber diameters, when synthetic fibers are used, the fiber diameter is preferably 0.006 mm to 0.075 mm, more preferably 0.010 mm to 0.055 mm, and even more preferably 0.016 mm to 0.050 mm. The fiber diameter can be measured using a microscope or the like.

[0031] The fiber diameter of fibers having a non-circular cross section is measured as follows. Figure 1 shows a schematic diagram of a cross section of a fiber having a non-circular cross section. Among the line segments connecting any two points on the circumference of any one fiber having a non-circular cross section, the line segment having the longest value is designated as A (A in Figure 1). Among the line segments that intersect perpendicularly with this A and connect any two points on the circumference of this fiber, the line segment having the longest value is designated as B (B in Figure 1), and the average value of A and B is calculated. This operation is performed on 30 fibers having a non-circular cross section (i.e., fibers having approximately the same aspect ratio) from the same lot, and the average of the 30 fibers is calculated to be the fiber diameter of the fiber having a non-circular cross section.

[0032] The length of the fibers is not particularly limited and can be appropriately selected depending on the purpose, but from the viewpoint of ease of dispersion in mud and clay minerals, it is preferably 1 mm to 25 mm, more preferably 1.5 mm to 16.5 mm, and even more preferably 2 mm to 15 mm. When regenerated cellulose fibers are used, the fiber length is preferably from 1 mm to 20 mm, more preferably from 1.5 mm to 16.5 mm, and even more preferably from 2 mm to 15 mm. When synthetic fibers are used, the length of the fibers is preferably from 1 mm to 25 mm, more preferably from 2 mm to 15 mm, and even more preferably from 3 mm to 10 mm. The length of the fibers can be measured using a microscope or the like.

[0033] The fiber content (dry weight %) is preferably 0.18% to 3.3%, more preferably 0.2% to 3.0%, and even more preferably 0.4% to 2.8%, based on the clay mineral. Among the fiber contents (% by dry weight), when synthetic fibers are used, the content is preferably 0.18% to 3.0%, more preferably 0.2% to 2.8%, and even more preferably 0.4% to 1.8%, relative to the clay mineral. If the fiber content (dry weight %) is less than 0.18%, the mud-adding material and the soil may not be integrated when mixed with the excavated soil, and the mixture of the mud-adding material and the soil may not have plasticity. Also, if the fiber content (dry weight %) exceeds 3.3%, the fluidity of the mixture of the mud-adding material and the excavated soil may decrease.

[0034] The fiber content is the ratio of the dry weight of the fiber to the weight of the clay mineral. Dry weight is the weight of the dried fiber. Specifically, it refers to the mass of the fiber when it is heated at 105°C for more than 2 hours and the weight change is within 0.25%.

[0035] <Other ingredients> The other components are not particularly limited and can be appropriately selected depending on the purpose. For example, clay minerals other than bentonite can be mentioned. The contents of other components are not particularly limited as long as they do not impair the performance of the mud-adding material, and can be appropriately selected depending on the purpose.

[0036] <Method of adding mud> There are no particular limitations on the method for producing the mud-adding material, and it may be appropriately selected depending on the purpose. For example, there may be mentioned a method in which fibers are added to a dispersion in which bentonite is dispersed in water, and the two are mixed.

[0037] (Shield method) The shield tunneling method according to the embodiment includes an excavation process, a plastic fluidization process, and a soil removal process, and further includes other processes as necessary.

[0038] <Drilling process> The excavation step is a step of excavating the target ground. The excavation method can be, for example, by scraping the ground with a cutter called a shield cutter.

[0039] <Plastic fluidization process> The plastic fluidization step is a step of injecting the mud-adding material into the soil generated in the excavation step to plastically fluidize the soil. The method of injecting the mud-adding material can be a method used in a normal shield tunneling method. The injection rate of the mud-adding agent when plastically fluidizing excavated soil and sand using the mud-adding agent means the ratio of the volume of the mud-adding agent to the volume of the excavated soil and sand (injection rate unit: %). The injection rate can be appropriately selected depending on the composition of the excavated soil and sand, the grain size of the excavated soil and sand, and the degree of plastic fluidity of the soil and sand mixed with the mud-adding agent (also called mixed soil), but is preferably 5% to 60%.

[0040] The soil removal process is a process of transporting the plastically fluidized soil out of the tunnel. The soil can be transported, for example, by using a belt conveyor.

[0041] <Other processes> The other steps are not particularly limited as long as they are normal shield tunneling processes and can be appropriately selected depending on the purpose. For example, steps such as assembling the tunnel walls can be included. EXAMPLES

[0042] Examples of the disclosed technology will be described below, but the disclosed technology is in no way limited to these examples.

[0043] In the examples, the following were used: Regenerated cellulose fiber A: Viscose rayon fiber (product name: SB, manufactured by Daiwabo Rayon Co., Ltd.) Synthetic fiber A: Polypropylene fiber (product name: PZ, manufactured by Yamatobo Co., Ltd.) Synthetic fiber B (biodegradable fiber): Poly-L-lactic acid / polybutylene succinate core-sheath composite fiber (product name: KK-PL, manufactured by Daiwabo Co., Ltd.) Core: Poly-L-lactic acid, sheath: Polybutylene succinate

[0044] <Tests on muddy materials with different fiber aspect ratios> (Examples 1-1 to 1-11, Comparative Examples 1-1 to 1-2) 1 L of tap water and 80 g of high swelling bentonite (Auxiliary Agent S, sold by Onoda Chemico Co., Ltd.) were mixed for 90 seconds in a juice mixer (FJM-601, manufactured by Fukai Kogyo Co., Ltd.) until the concentration of bentonite became 80 kg / m 3 A bentonite dispersion (mud water) was prepared as follows. The regenerated cellulose fiber A having the physical properties such as the aspect ratio shown in Table 1 was added to the obtained bentonite dispersion so that the dry weight of the fiber relative to the weight of the bentonite was 0.82%, and the mixture was stirred in a juice mixer for 1 minute to obtain a muddy material. The obtained muddy material was transferred to a beaker and left to stand for 1 day. The cylinder flow of the muddy material after standing was measured based on the cylinder method (a test method for air mortar and air milk using a cylinder with a diameter of 80 mm and a height of 80 mm) specified in JHS A 313-1992, and it was evaluated based on the following evaluation criteria. If the cylinder flow of the muddy material is 160 mm to 300 mm, plastic fluidity can be imparted when the muddy material is mixed with soil and sand, so the evaluation criteria were based on that value. The evaluation results are also shown in Table 1. In addition, the dry weight of 0.82% means that the ratio of the weight of dried fiber to the weight of bentonite is 0.82%. The measured cylinder flow of the bentonite dispersion (i.e., when regenerated cellulose fiber A was not added) was 353 mm. The term "poor uniform dispersion of fibers" refers to the following: when bentonite and regenerated cellulose fiber A are mixed and then left to stand for 3 minutes, a sediment that is a mass of regenerated cellulose fiber A is generated at the bottom of the beaker, or a mass of bentonite and regenerated cellulose fiber A is formed and settles at the bottom of the beaker, and only water can be observed at the top of the beaker. -Evaluation criteria- ○: Cylinder flow is 160mm~300mm ×: Cylinder flow is less than 160 mm or more than 300 mm, or the uniform dispersion of fibers is poor (visual evaluation)

[0045] [Table 1]

[0046] In Comparative Example 1-1, the aspect ratio of the fibers was small, and the entanglement between the fibers and the muddy water (bentonite water) was weak, so that the fibers sank in the muddy water and were not uniformly dispersed. In Comparative Example 1-2, since the aspect ratio of the fibers was large, fiber clumps were formed in the muddy water, and the bentonite and the fibers were separated, so that the cylinder flow measurement was not possible. The results in Table 1 show that fibers with an aspect ratio of 100 to 1,450 have a cylinder flow in the range of 160 mm to 300 mm, and also have good uniform dispersion between the bentonite and fibers in the mud-adding material, thereby imparting plastic fluidity to the excavated soil.

[0047] <Tests on muddy materials with different fiber content> (Examples 2-1 to 2-9, Comparative Examples 2-1 to 2-2) 1 L of tap water and 80 g of high swelling bentonite (Auxiliary Agent S, sold by Onoda Chemico Co., Ltd.) were mixed for 90 seconds in a juice mixer (FJM-601, manufactured by Fukai Kogyo Co., Ltd.) until the concentration of bentonite became 80 kg / m 3 A bentonite dispersion (mud water) was prepared as follows. The regenerated cellulose fiber A having the aspect ratio and the like shown in Table 2 was added to the obtained bentonite dispersion so that the dry weight of the fiber relative to the weight of the bentonite was the amount shown in Table 2, and the mixture was stirred for 1 minute in a juice mixer to obtain a muddy material. The obtained muddy material was transferred to a beaker and left to stand for 1 day. After standing, the cylinder flow of the muddy material was measured based on the cylinder method (a test method for air mortar and air milk using a cylinder with a diameter of 80 mm and a height of 80 mm) specified in JHS A 313-1992, and it was evaluated based on the following evaluation criteria. The evaluation results are also shown in Table 2. The measured cylinder flow of the bentonite dispersion without the addition of regenerated cellulose fiber A was 353 mm. In addition, poor uniform dispersion of fibers means that when bentonite and regenerated cellulose fiber A are mixed and then left to stand for 3 minutes, a sediment consisting of lumps of regenerated cellulose fiber A forms at the bottom of the beaker, or lumps of bentonite and regenerated cellulose fiber A are formed and settle to the bottom of the beaker, and only water can be observed at the top of the beaker. -Evaluation criteria- ○: Cylinder flow is 160mm~300mm ×: Cylinder flow is less than 160 mm or more than 300 mm, or the uniform dispersion of fibers is poor (visual evaluation)

[0048] [Table 2]

[0049] In Comparative Example 2-1, the aspect ratio of the fibers was small and the entanglement between the fibers was weak, so the fibers sank in the muddy water and were not uniformly dispersed at dry weights of 0.41%, 0.82%, 1.6%, and 2.5%. In Comparative Example 2-2, the aspect ratio of the fibers was large at dry weights of 0.41%, 0.82%, and 1.6%, so the fibers formed clumps in the muddy water and the bentonite and fibers separated, making it impossible to measure the cylinder flow. From the results in Table 2, it was found that for fibers with an aspect ratio of 100 to 1,450, even when the weight (dry weight) of the fiber in the mud-adding material was changed, the cylinder flow was in the range of 160mm to 300mm, the uniform dispersion of the fiber was good, and plastic fluidity was imparted to the excavated soil. In addition, between 0.41% and 2.5% of the dry weight of fiber, the measured cylinder flow tended to decrease as the amount of fiber added was increased.

[0050] <Tests on muddy materials with different fiber types> (Examples 3-1 to 3-16) 1 L of tap water and 80 g of high swelling bentonite (Auxiliary Agent S, sold by Onoda Chemico Co., Ltd.) were mixed for 90 seconds in a juice mixer (FJM-601, manufactured by Fukai Kogyo Co., Ltd.) until the concentration of bentonite became 80 kg / m 3 A bentonite dispersion (mud water) was prepared as follows. Fibers (regenerated cellulose fiber A, synthetic fiber A, synthetic fiber B (biodegradable fiber)) having the physical properties shown in Table 3, such as the aspect ratio, were added to the obtained bentonite dispersion so that the wet weight of the fibers relative to the weight of the bentonite was 1%, and the mixture was stirred for 1 minute in a juice mixer to obtain a mud-added material. The dry weight relative to the bentonite when the wet weight was 1% was 0.41% for regenerated cellulose fiber A, 0.74% for synthetic fiber A, and 1% for synthetic fiber B, respectively. The obtained muddy material was transferred to a beaker and left to stand for one day. After standing, the muddy material was measured for cylinder flow based on the cylinder method (a test method for air mortar and air milk using a cylinder with a diameter of 80 mm and a height of 80 mm) specified in JHS A 313-1992, and evaluated based on the following evaluation criteria. The evaluation results are shown in Table 3. The measured cylinder flow of the bentonite dispersion to which no fiber was added was 353 mm. Furthermore, the term "poor uniform dispersion of fiber" refers to the following: when bentonite and fiber are mixed and then left to stand for 3 minutes, a sediment consisting of clumps of fiber is generated at the bottom of the beaker, or clumps of bentonite and fiber are formed and settle at the bottom of the beaker, and only water is observed at the top of the beaker. -Evaluation criteria- ○: Cylinder flow is 160mm~300mm ×: Cylinder flow is less than 160 mm or more than 300 mm, or the uniform dispersion of fibers is poor (visual evaluation)

[0051] [Table 3]

[0052] From the results in Table 3, it was found that fibers with an aspect ratio of 100 to 1,450 have a cylinder flow in the range of 160 mm to 300 mm, even when the type of fiber is changed, and the fibers have good uniform dispersion, and can impart plastic fluidity to the excavated soil and sand. It was also made clear that this is not dependent on the type of fiber. Furthermore, in comparison with Examples 3-1 to 3-15, when the aspect ratio of regenerated cellulose fiber A was changed in the range of 154 to 1,154, the cylinder flow measurement value was 226 mm to 266 mm. In contrast, when the aspect ratio of synthetic fiber A was changed in the range of 102 to 556, the cylinder flow measurement value was 174 mm to 253 mm, and the range of the cylinder flow measurement value was wider than that of regenerated cellulose fiber A. In other words, it is considered that the aspect ratio of synthetic fiber A has a larger effect on the cylinder flow measurement value than the aspect ratio of regenerated cellulose fiber A. In addition, since the results in Table 3 are for a wet weight of 1% and a small amount of addition, it was found that the aspect ratio of synthetic fiber A has a large effect on the cylinder flow value result even if the amount of addition is small.

[0053] <Tests on muddy materials with different types or concentrations of bentonite> (Examples 4-1 to 4-20, Comparative Examples 4-1 to 4-7) High swelling bentonite (auxiliary agent S, sold by Onoda Chemico Co., Ltd.) or low swelling bentonite (auxiliary agent M, sold by Onoda Chemico Co., Ltd.) was added to 1 L of tap water and stirred for 90 seconds in a juice mixer to prepare bentonite dispersions (mud water) of each concentration as shown in Table 4. Regenerated cellulose fiber A having the aspect ratios shown in Table 4 was added to the obtained bentonite dispersion so that the dry weight of the fiber relative to the weight of the bentonite was 1.63%, and the mixture was stirred for 1 minute in a juice mixer to obtain a muddy material. The muddy material obtained was transferred to a beaker and left to stand for 1 day. After standing, the cylinder flow of the muddy material was measured based on the cylinder method (test method for air mortar and air milk using a cylinder with a diameter of 80 mm and a height of 80 mm) specified in JHS A 313-1992, and it was evaluated based on the following evaluation criteria. In addition, poor uniform dispersion of fibers means that when bentonite and fiber are mixed and then left to stand for 3 minutes, a sediment consisting of clumps of fiber is formed at the bottom of the beaker, or clumps of bentonite and fiber are formed and settle at the bottom of the beaker, and only water is observed at the top of the beaker. -Evaluation criteria- ○: Cylinder flow is 160mm~300mm ×: Cylinder flow is less than 160 mm or more than 300 mm, or the uniform dispersion of fibers is poor (visual evaluation)

[0054] [Table 4]

[0055] In Comparative Example 4-4, the aspect ratio of the fiber was small, and the entanglement between the fiber and the muddy water (bentonite water) was weak, so the fiber sank in the muddy water and was not uniformly dispersed. In Comparative Example 4-5, the aspect ratio of the fiber was large, so the fiber clumps formed in the muddy water and the bentonite and the fiber were separated, making it impossible to measure the cylinder flow. The results in Table 4 show that fibers with an aspect ratio of 100 to 1,450 have a cylinder flow in the range of 160 mm to 300 mm, even when the type or concentration of bentonite is changed, and the fibers have good uniform dispersion, providing plastic fluidity to the excavated soil and sand.

[0056] (Examples 4-21 to 4-34, Comparative Examples 4-8 to 4-11) High swelling bentonite (auxiliary agent S, sold by Onoda Chemico Co., Ltd.) or low swelling bentonite (auxiliary agent M, sold by Onoda Chemico Co., Ltd.) was added to 1 L of tap water and stirred for 90 seconds in a juice mixer to prepare bentonite dispersions (mud water) of each concentration as shown in Table 5. Synthetic fiber A with the aspect ratios shown in Table 5 was added to the obtained bentonite dispersion so that the dry weight of the fiber relative to the weight of the bentonite was 0.74%, and the mixture was stirred for 1 minute in a juice mixer to obtain a muddy material. The muddy material obtained was transferred to a beaker and left to stand for 1 day. After standing, the cylinder flow of the muddy material was measured based on the cylinder method (test method for air mortar and air milk using a cylinder with a diameter of 80 mm and a height of 80 mm) specified in JHS A 313-1992, and it was evaluated based on the following evaluation criteria. In addition, poor uniform dispersion of fibers means that when bentonite and fiber are mixed and then left to stand for 3 minutes, a sediment consisting of clumps of fiber is formed at the bottom of the beaker, or clumps of bentonite and fiber are formed and settle at the bottom of the beaker, and only water is observed at the top of the beaker. -Evaluation criteria- ○: Cylinder flow is 160mm~300mm ×: Cylinder flow is less than 160 mm or more than 300 mm, or the uniform dispersion of fibers is poor (visual evaluation)

[0057] [Table 5]

[0058] The results in Tables 4 and 5 show that fibers with an aspect ratio of 100 to 1,450, regardless of the type of fiber, have a cylinder flow in the range of 160 mm to 300 mm even when the type or concentration of bentonite is changed, and the fibers have good uniform dispersion, providing plastic fluidity to the excavated soil.

[0059] <Evaluation of adding mud-adding materials to soil> (Examples 5-1 to 5-8, Comparative Example 5-1) Gravel soil was used as the model soil. Water was added to the model soil to make the water content 5%. The mud additives shown in Table 6 were added to the model soil so that the injection rate was 20%, and mixed. After mixing, the mini-slump and table flow were measured. The mini-slump was measured based on JIS A 1171:2000 (Testing method for polymer cement mortar), and the table flow was measured based on JIS R 5201:1997 (Physical testing method for cement). The measurement results are shown in Table 5. In addition to the mini-slump and table flow tests, the condition of the simulated soil mixed with the mud additive was visually observed and evaluated based on the following evaluation criteria. The evaluation results are shown in Table 6. The fiber used was regenerated cellulose fiber A, with a fiber diameter of 0.013 mm, a fiber length of 5 mm, an aspect ratio of 385, and a fineness (dtex) of 1.7. -Evaluation criteria- ○: The simulated soil is cohesive and has fluidity ×: The simulated soil is not cohesive or has no fluidity. Or, the uniform dispersion of the fibers is poor (visual evaluation).

[0060] [Table 6]

[0061] Comparative Example 5-1, which contained only gravel soil, showed no fluidity at all. From the results in Table 6, it became clear that mixing the mud-adding material according to this embodiment with soil and sand can give it plastic fluidity. This was the same result regardless of the type, concentration, or fiber content of bentonite. Therefore, it was found that a mud-adding material containing fibers with an aspect ratio of 100 to 1,450 and clay minerals can impart plastic fluidity to excavated soil and sand.

Claims

1. Clay minerals and At least one fiber selected from regenerated cellulose fibers, semi-synthetic fibers, and synthetic fibers, the fiber having an aspect ratio of 100 to 1,450; A mud-adding material characterized by containing.

2. The mud-adding material according to claim 1, wherein the synthetic fiber is at least one selected from polyolefin-based fibers and biodegradable fibers.

3. The regenerated cellulose fiber is a viscose rayon fiber, The polyolefin fiber is a polypropylene fiber, The mud-adding material according to claim 2, wherein the biodegradable fiber is at least one selected from polylactic acid fiber and polylactic acid / polybutylene succinate composite fiber.

4. The mud-adding material according to claim 1, wherein the clay mineral is a swelling clay mineral.

5. The mud-adding material according to claim 4, wherein the swelling clay mineral is montmorillonite.

6. The mud-adding material according to claim 5, wherein the swelling clay mineral is bentonite having montmorillonite as a main component.

7. The mud-adding material according to claim 1 or 2, wherein the fiber diameter of the fibers is 0.006 mm to 0.1 mm.

8. The mud-adding material according to claim 1 or 2, wherein the fiber content (dry weight%) is 0.18% to 3.3% with respect to the clay mineral.

9. A shield construction method comprising adding the mud-adding material according to claim 1 or 2.

10. The fiber for use in mud-adding materials is at least one selected from regenerated cellulose fibers, semi-synthetic fibers, and synthetic fibers, and has an aspect ratio of 100 to 1,450.

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