Cement composition for spray construction to tunnel surface and method for reinforcing tunnel deep underground

Abstract

To provide a cement composition for construction, which can be quickly and efficiently constructed over a wide range inside a tunnel provided deep underground, and can protect a tunnel from cracks and groundwater inflow for a long period after construction, and a construction method therefor.SOLUTION: A cement composition is intended for spray construction to a surface of a tunnel deep underground to reinforce a tunnel, and is characterized by comprising cement, aggregate, a concretion agent, and water. When the cement composition of the present invention is sprayed onto the surface of the tunnel deep underground, not only does the cement composition harden on the sprayed surface of the tunnel, but the concretion agent penetrates into a surface layer of the tunnel, thereby densifying the surface layer as well, thereby protecting the tunnel from cracking and groundwater inflow for a long period of time. Furthermore, the present invention also provides a method for reinforcing the tunnel deep underground using the cement composition of the present invention.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a cement composition for spray application onto tunnel surfaces, and a method for reinforcing tunnels deep underground by spraying the cement composition onto the tunnel surfaces. [Background technology]

[0002] Radioactive waste generated during the operation of nuclear power plants is ultimately buried in tunnels dug deep underground in order to isolate it from the human environment. Figure 13(a) is a schematic diagram of an intermediate depth disposal facility for radioactive waste, and Figure 13(b) is a vertical cross-sectional view of the buried cavity d shown in part (b) of Figure 13(a).

[0003] (Note that Figures 13(a) and (b) are based on Figure 4 in "The Background and Concept of Establishing Regulatory Standards for Intermediate Depth Disposal" by Hiroomi Aoki et al., Journal of the Atomic Energy Society of Japan, Vol. 65, No. 1, p. 21 (2023), with the symbols deleted and added.)

[0004] As shown in Figure 13(a), the intermediate depth disposal facility for radioactive waste comprises a surface facility a, an access tunnel b leading underground, a main tunnel c, a buried cavity d, and a connecting tunnel e.

[0005] As shown in Figure 13(b), if each tunnel is exemplified by a buried cavity d, a horseshoe-shaped tunnel f is covered with sprayed concrete g, and rock bolt holes (not shown) are drilled into the surface of the tunnel f covered with the sprayed concrete g until they reach the bedrock layer k deep inside the tunnel. Rock bolts h are inserted into these rock bolt holes, and mortar or the like is injected into the rock bolt holes and allowed to harden, so that together with the shotcrete g, the loosened area i of the bedrock layer around the tunnel is fixed to the deep bedrock layer k via the rock bolts h, providing support.

[0006] However, not only in tunnels storing radioactive waste, but in rock masses deep underground, (1) the distribution of poor geological quality such as fault fracture zones and porous layers is expected. (2) Furthermore, in the rock mass surrounding tunnels in geological strata deeper than 70 m underground, in addition to primary cracks, there is a risk of loosening cracks occurring due to excavation. (3) Furthermore, as shown in Figure 13(b), the shotcrete g sprayed into tunnel f immediately after excavation is subject to cracks caused by external forces and the external environment (temperature, drying, construction quality, etc.).

[0007] In order to protect the inside of the tunnel from groundwater inflow and cracks in the tunnel itself for a long period of time, the highly permeable areas caused by the above (1) to (3) have conventionally been appropriately filled by injecting grout.

[0008] However, the durability of cement-based materials is said to be 50 to 100 years, and they cannot withstand use for more than 100 years, so there is a demand for an injection material that can replace grout and has long-term durability.

[0009] Patent Document 1 discloses that a mixed solution of an epoxy compound (hardening compound), an epoxy hardener (hardening agent), calcium chloride, and sodium bicarbonate is injected into holes in a sandstone block to obtain a repaired block (see Examples 1-2). As a result, calcium carbonate particles (calcite structure of calcium carbonate) are formed over the entire surface of the repaired block. It also discloses a method for repairing ground, etc., by drilling an injection port from the surface of the bedrock (ground) toward the crack or junk part instead of using a sandstone block, and then injecting the mixed solution through the injection port.

[0010] Furthermore, Non-Patent Documents 1 to 3 disclose that in a test tunnel 350 m underground, the tunnel wall and bottom were excavated, multiple holes were made, and a concretion agent was injected into the holes. According to Patent Document 2 (Japanese Patent No. 6889508) cited in Non-Patent Documents 1 to 3, the concretion agent is, for example, Ca 2+ Ion exchange resin with adsorbed ions, Ca 2+Examples of such a combination include a liquid or sheet containing capsules that encapsulate and release ions, and an ion source that supplies bicarbonate ions. According to the concretion agents of Non-Patent Documents 1 to 3, Ca released from the concretion agent 2+ The ions react with bicarbonate ions from the ion source to form sparingly soluble calcium carbonate, which densifies the underground rock around the hole and reduces the permeability of the underground rock. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2022-48720 [Patent Document 2] Patent No. 6889508 [Non-patent literature]

[0012] [Non-Patent Document 1] Eiichi Yoshida, Koji Yamamoto et al., "Underground Demonstration Test Study on Self-Sealing of Water Pathway Cracks by Concretion," Abstracts of the 129th Annual Meeting of the Geological Society of Japan, pp. 441-442, Geological Society of Japan, 2022 [Non-patent document 2] Eiichi Yoshida, Koji Yamamoto et al., "Study on Self-Sealing of EDZ and Water Pathway Cracks by Concretion," Proceedings of the 2021 Japan Society of Engineering Geology Research Presentation Meeting, Japan Society of Engineering Geology, 2021 [Non-patent document 3] Eiichi Yoshida, Koji Yamamoto, Yoshihiro Asahara et al., "Demonstration Test Study on Self-Sealing of EDZ and Water Pathway Cracks by Concretion," Proceedings of the 2022 Japan Society of Engineering Geology Research Presentation Meeting, Japan Society of Engineering Geology, 2022 Summary of the Invention [Problem to be solved by the invention]

[0013] However, while the method for repairing rock masses and the like described in Patent Document 1 can pinpoint and repair cracked or junk rock masses, it takes time and effort to individually identify the cracked or junk rock masses on the inner surface of a tunnel and repair each of the identified parts. It also takes time and effort to apply the method for repairing rock masses and the like described in Patent Document 1 over a wide area of ​​the inner surface of a tunnel. The same applies to the methods disclosed in Non-Patent Documents 1 to 3, in which a concretion agent is injected into the wall or bottom of a tunnel to form concretions in the surrounding area of ​​the tunnel.

[0014] The object of the present invention, which has been made in view of the above problems, is to provide a cement composition for construction and a construction method which can be quickly and efficiently constructed over a wide area inside a tunnel located deep underground and which can protect the tunnel from cracks and groundwater inflow for a long period after construction. [Means for solving the problem]

[0015] The present inventors have conducted extensive research to achieve the above object, and as a result have discovered that by simply spraying mortar containing a concretion agent onto the surface of a tunnel located deep underground, the inner surface and surface layer of the tunnel to which the mortar is sprayed can be densified using concretion technology, thereby protecting the interior of the tunnel from tunnel collapse and groundwater inflow for a longer period than conventional methods, and have completed the present invention.

[0016] That is, it has been found that the above-mentioned object can be achieved by a cement composition for spraying onto the surface of a tunnel located deep underground to reinforce the tunnel, the cement composition comprising cement, aggregate, a concretion agent, and water.

[0017] It is also preferred that the concretion agent contains sodium bicarbonate and a calcium ion source.

[0018] Furthermore, it is preferable that the tunnel is a tunnel for storing radioactive waste.

[0019] The above object can also be achieved by a method for reinforcing a tunnel located deep underground, which includes a hardened layer forming step of spraying the cement composition of the present invention onto a tunnel located deep underground to obtain a hardened layer of the cement composition.

[0020] Furthermore, the method for reinforcing a tunnel deep underground of the present invention preferably further comprises the following steps: a hole forming step of forming a hole from the surface of the hardened layer of the cement composition in the tunnel to the bedrock layer deep in the tunnel; a rock bolt inserting step of inserting a rock bolt into the hole; an injection step of injecting a mixed liquid of a cement-based hardener and a concretion agent into the hole before or after the rock bolt inserting step; and a fixing step of hardening the cement-based hardener and fixing the loosened area of ​​the bedrock around the tunnel to the bedrock layer deep in the tunnel via the rock bolt, thereby stabilizing the bedrock around the tunnel. [Effects of the Invention]

[0021] According to the cement composition for spraying onto tunnel surfaces and the method for reinforcing tunnels deep underground of the present invention, when the cement composition of the present invention is sprayed onto the surface of a tunnel located deep underground, not only does the cement composition harden on the sprayed tunnel surface, but the concretion agent penetrates into the tunnel surface layer, densifying the tunnel surface layer as well, thereby protecting the tunnel from cracks and groundwater inflow for a long period of time.Furthermore, since the above effects can be obtained simply by replacing a conventional cement composition for spraying with the cement composition of the present invention, it is possible to apply the composition quickly and efficiently over a wide area, just like conventional spraying onto tunnel surfaces. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic cross-sectional view of a tunnel reinforced by spraying the cement composition of the present invention. [Figure 2] FIG. 1 is a flow chart showing a method for reinforcing a tunnel deep underground according to the present invention. [Figure 3]1 is a schematic cross-sectional view showing the structure of the surrounding area of ​​a tunnel reinforced by the method of reinforcing a tunnel deep underground according to the present invention. FIG. [Figure 4] 1A is a photograph in place of a drawing showing specimens 1 and 2 of the embodiment, and FIG. 1B is a photograph in place of a drawing showing a sample of specimens 1 and 2 bonded with silicone for concretion treatment. [Figure 5] In the working example, (a) is a photograph in place of a drawing showing the state in which a mixture of hardener and concretion agent is poured into the sample of Figure 4(b), and (b) is a photograph in place of a drawing showing a laminate of specimens 1 and 2 and a hardened layer of hardener and concretion agent. [Figure 6] 6(a) is a photograph showing the laminate of FIG. 5(b) (the state of water path formation) from the bottom, and FIG. 6(b) is a photograph showing the concretion treatment of the laminate of FIG. 6(a) in the embodiment. [Figure 7] 1 is a graph showing the results of an indoor water permeability test for evaluating the influence of the presence or absence of concretion treatment on porous concrete in an example. [Figure 8] FIG. 1 is a schematic perspective view of a cylindrical specimen 3 used in an X-ray microscope observation test to evaluate the influence of the presence or absence of a concretion treatment on ordinary concrete in an embodiment. [Figure 9] 9 is an element map obtained by an X-ray microscope observation test, showing a cross section of the cylindrical specimen 3 of the example taken along line VIII-VIII in FIG. 8. The vertical axis represents calcium concentration. [Figure 10] 10 shows a Ca profile of the area surrounded by the white line in Fig. 9 of the example. The vertical axis represents the X-ray intensity, and the horizontal axis represents the length of the specimen 3 in the diameter direction. [Figure 11] FIG. 3 is a plan view of specimen 3-1 of the example. [Figure 12] In the working examples, (a) is a photograph in lieu of a drawing showing the results of elemental mapping of the cut surface of specimen 3-1, and (b) is a photograph in lieu of a drawing showing the results of elemental mapping of the cut surface of a disk-shaped pumice tuff (hereinafter referred to as specimen 3-0) to which the mixture of hardener and concretion agent has not been applied. [Figure 13](a) is a schematic diagram of a conventional intermediate depth disposal facility for radioactive waste, and (b) is a vertical cross-sectional view of the buried cavity d shown in part (b) of the same figure (a). DETAILED DESCRIPTION OF THE INVENTION

[0023] <Cement composition for spray application to tunnel surfaces> The cement composition of the present invention for spray application onto the surface of a tunnel is a cement composition for reinforcing a tunnel located deep underground.

[0024] "Deep underground" refers to the area 70 meters or more below the surface. Examples of tunnels include access tunnels, connecting tunnels, main tunnels, and buried cavities of intermediate depth disposal facilities for radioactive waste, but this does not limit the scope to these tunnels; it also includes tunnels located deep underground, such as those used in coal mines, mines, and other research facilities.

[0025] The cross-sectional shape of the tunnel is not limited to a horseshoe shape, but can take various shapes such as a circle, an oval, a square (including a rectangle), and a hexagon.

[0026] In the case of a buried cavity with a horseshoe-shaped cross section, the size of the tunnel is, for example, approximately 10 to 20 m wide and 15 to 20 m high, but this is not limited to this and any size can be used depending on the purpose of the tunnel.

[0027] The cement composition of the present invention for spray application to the surface of a tunnel comprises cement, aggregate, a concreting agent, and water.

[0028] [cement] Cement is an inorganic binder that hardens when mixed with water, and hydraulic cement is used in the present invention. As hydraulic cement, simple cement such as Portland cement (JIS R5210), hydraulic lime, Roman cement, or natural cement may be used, or mixed cement such as lime-blended cement or mixed Portland cement (JIS R5211, R5212, R5213) may be used.

[0029] [water] The water to be mixed in the cement composition is not limited to pure water, but tap water, river water, and lake water can also be used.

[0030] [aggregate] Aggregates are generally used in the production of concrete and are added to suppress heat generation due to the hydration reaction of the cement composition, suppress shrinkage, and reduce the amount of cement used to cut costs.Aggregates are divided into coarse aggregate and fine aggregate, with coarse aggregate being retained by 85% or more by mass on a 5mm sieve, and fine aggregate being passed through a 5mm sieve and 100% by mass passing through a 10mm sieve.

[0031] Examples of aggregate materials include river sand, mountain sand, sea sand, blast furnace slag, and copper slag.

[0032] [Concretion agent] Before explaining the concretion agent, the mechanism of concretion will be explained.

[0033] Concretions are spherical rock masses that are formed when the gaps between the detrital particles (sand or mud) in sedimentary rock are filled with minerals, making them extremely dense and hard. The mechanism of concretions formation is that, for example, in the case of a horn shell, bicarbonate ions (HCO3 - ) or carbonate ions (CO3 2- ) combines with calcium ions in seawater to form calcium carbonate, which then grows round like a balloon expanding.

[0034] This can be expressed as the formula below.

[0035] R·CH2COOH (organic matter) → R·H + HCO3 - + H + HCO3 - → CO3 2- + H + CO3 2- + Ca2+ (seawater derived) →CaCO3 Concretions include those whose main component is calcium carbonate as described above, as well as carbonates containing iron, silica, and some magnesium. The concretion agent of the present invention is a concretion agent that produces concretions whose main component is calcium carbonate.

[0036] Therefore, in the present invention, the concretion agent contains at least a bicarbonate ion source and / or a carbonate ion source as an anion source. Examples of bicarbonate ion sources include sodium hydrogen carbonate (baking soda), and examples of carbonate ion sources include sodium carbonate (sodium carbonate). Among these, from the viewpoints of availability and cost, it is preferable that the concretion agent contains sodium hydrogen carbonate as the bicarbonate ion source.

[0037] In addition, when the concretion agent employs a bicarbonate ion source and / or carbonate ion source as an anion source but does not include a calcium ion source as a cation source, the calcium ions required to form concretions are supplied from the rock around the tunnel, the deep rock layer, calcium ions dissolved in the water in these rock layers, as well as from cement, aggregate, and water (for example, when hard water is used).

[0038] However, in order to increase the density of the concretions, it is preferred that the concretion agent further contains a calcium ion source in addition to the anion source.

[0039] Examples of calcium ion sources include calcium chloride, calcium hydroxide (slaked lime), calcium formate, calcium acetate, calcium citrate, etc. Among these, calcium formate is preferably used as the calcium ion source because it also acts as a cement hardening accelerator.

[0040] It is particularly preferred that the concretion agent comprises sodium bicarbonate and a source of calcium ions.

[0041] [Other ingredients] Furthermore, as other components, it may optionally contain admixtures such as expansive agents, bulking agents and limestone fine powder, as well as admixtures such as air-entraining agents (AE agents), water-reducing agents (AE water-reducing agents, water-reducing agents, high-performance AE water-reducing agents, etc.), superplasticizers, setting / hardening regulators, accelerators and waterproofing agents.

[0042] The cement composition of the present invention can be prepared, for example, by powder-mixing cement and any powder components added thereto, adding water, a concreting agent, and any admixtures to the powder mixture, kneading the mixture to form a paste, mixing the mixture with aggregate, and further kneading the mixture.

[0043] Figure 1 is a schematic cross-sectional view of a tunnel reinforced by spraying the cement composition of the present invention. As shown in the figure, compared to the deep rock mass k, the rock mass i around the tunnel, surrounded by a dashed line, often has a loosened region containing loosened cracks z due to excavation in addition to primary cracks (not shown). In addition, a fault fracture zone w may exist across the tunnel or its vicinity.

[0044] However, according to the present invention, the cement composition of the present invention is sprayed onto the surface of a tunnel f, leaving a hardened layer g, and the concretion agent penetrates not only into this hardened layer g but also into the rock mass i around the tunnel, as shown by the arrow in Figure 1. This causes the hardened layer g and the rock mass i around the tunnel to become densified through the formation of concretions, and primary cracks in the rock mass i around the tunnel, loosening cracks z caused by excavation, and fault fracture zones w are also filled with concretions. The densification effect of the concretions on the hardened layer g and the rock mass i around the tunnel can be maintained for a longer period than with hardened cement alone, making it possible to protect the tunnel from cracks and groundwater inflow for a longer period than before.

[0045] Furthermore, since the above-mentioned effects can be obtained simply by replacing conventional cement compositions for spray application with the cement composition of the present invention, it is possible to apply the composition quickly and efficiently over a wide area, similar to conventional spray application to tunnel surfaces.

[0046] <Method of reinforcing tunnels deep underground> The method of reinforcing a tunnel deep underground according to the present invention will be explained with reference to Fig. 2. Fig. 2 is a flow diagram showing the method of reinforcing a tunnel deep underground according to the present invention, and shows two cases: one in which the tunnel is supported by spraying a cement composition, and the other in which the tunnel is supported by spraying a cement composition and then installing rock bolts.

[0047] First, the method for reinforcing a tunnel deep underground according to the present invention will be described using an example in which the tunnel is supported by spraying a cement composition. That is, the method for reinforcing a tunnel deep underground according to the present invention includes a hardened layer forming step (S110), as shown in FIG.

[0048] [Hardened layer formation process (S110)] In this step, the cement composition of the present invention is sprayed into a tunnel provided deep underground to obtain a hardened layer of the cement composition. Note that the cement composition of the present invention, the deep underground, and the tunnel have already been explained, so further explanation will be omitted here.

[0049] The cement composition can be sprayed into the tunnel by a conventionally known method, and for example, a wet method may be used in which a premixed cement composition is placed in a spraying machine, transported by compressed air or a pump, and sprayed from a nozzle, or a dry method may be used in which a dry mix of the cement composition excluding water is placed in a spraying machine, transported to a nozzle by compressed air, and water is added near the nozzle and sprayed.

[0050] The cement composition may be sprayed onto the tunnel to any thickness, but is, for example, within the range of 8 cm to 30 cm.

[0051] The cement composition develops strength immediately after being sprayed into the tunnel, and a hardened layer of the cement composition is obtained, so no curing period is required (this is the hardened layer forming step (S110)).

[0052] According to the method for reinforcing deep underground tunnels of the present invention, as shown in Figure 1, a hardened layer g of the cement composition of the present invention is formed on the surface of tunnel f, so that the concretion agent penetrates not only into the hardened layer g but also into the rock mass i surrounding the tunnel, and the hardened layer g and the rock mass i surrounding the tunnel are densified by the formation of concretions. This allows the tunnel to be protected from cracks and groundwater inflow for a long period of time. Furthermore, because the process itself is the same as conventional spraying, it can be applied quickly and efficiently over a wide area, just like conventional spraying on the surface of tunnels.

[0053] Next, the method of reinforcing a tunnel deep underground according to the present invention will be explained using as an example a case in which a cement composition is sprayed onto the tunnel and then supported by installing rock bolts.

[0054] In this case, the method of reinforcing a deep underground tunnel of the present invention includes a hardened layer forming process (S110), a hole forming process (S120), a rock bolt inserting process (S130), an injection process (S140), and a fixing process (S150), as shown in Figure 2.

[0055] The hardened layer forming step (S110) has already been explained in the case of supporting a tunnel by spraying a cement composition, and therefore will not be explained here. After the hardened layer forming step (S110), the process proceeds to the hole forming step (S120).

[0056] [Hole formation process (S120)] In this step, a hole is formed from the surface of the hardened layer of the cement composition in the tunnel to reach the bedrock layer deep in the tunnel.

[0057] As already mentioned, the rock mass around the tunnel i (see Figure 1), which forms the surface of the tunnel, has primary cracks, as well as the risk of loosening cracks occurring during excavation, which may result in a loosened area.

[0058] In the present invention, in order to install a rock bolt to stabilize the bedrock around the tunnel, a hole m (see Figure 3) is formed to serve as the rock bolt hole, extending from the surface of the hardened layer g of the cement composition to the bedrock layer deep inside the tunnel.

[0059] Since the hole portion is a rock bolt hole for inserting a rock bolt, the diameter of the hole portion is larger than the diameter of the rock bolt, for example, in the range of 45 mm to 50 mm, and the length of the hole portion is, for example, in the range of 3 m to 4 m (this is the hole portion forming process (S120)).

[0060] [Rock bolt insertion process (S130)] In this step, a rock bolt is inserted into the hole. Examples of the rock bolt 12 (see FIG. 3) include a deformed steel bar, a fully threaded steel bar, and a twisted steel bar. The rock bolt can be inserted in accordance with a conventionally known rock bolt construction method, and a detailed description thereof will be omitted here (this concludes the rock bolt insertion step (S130)).

[0061] [Injection process (S140)] In this step, a mixed liquid of a cement-based hardening agent and a concretion agent is injected into the hole before or after the rock bolt inserting step (S130).

[0062] Cement-based hardeners are generally mortar or cement milk. Mortar contains only fine aggregate, not coarse aggregate, while cement milk does not contain aggregate itself.

[0063] The concretion agent may be appropriately selected from the blends of concretion agents contained in the cement composition of the present invention. Prior to this step, a mixed solution of a cement-based hardening agent and a concretion agent is prepared. As described above, the mixed solution of the hardening agent and the concretion agent is injected into the hole before or after the rock bolt insertion step (S130). If it is injected before the rock bolt insertion step (S130), it is called a pre-filling method, and if it is injected after the rock bolt insertion step (S130), it is called a post-injection method.

[0064] The injection of the mixture of cement-based hardener and concretion agent into the hole can be done using a tip-fixation method, in which a packer or the like is used to separate an area of ​​the rock layer deep inside the tunnel in the hole, and the mixture of cement-based hardener and concretion agent is injected only into this area to fix only the tip of the rock bolt, or a full-surface fixation method, in which the mixture of cement-based hardener and concretion agent is injected along the entire length of the hole to fix the entire length of the rock bolt.

[0065] However, from the viewpoint of stabilizing the rock around the tunnel, which may become a loose area, it is preferable to adopt the full-surface anchorage method.

[0066] After or before the injection of the mixture of cement-based hardener and concretion agent into the hole, a nut 16 (see Figure 3), a bearing plate 18 (see Figure 3), etc. are attached to the head of the rock bolt (this is the injection process (S140)).

[0067] [Fixing process (S150)] In this process, the cement-based hardener is hardened, and the loosened areas of the rock around the tunnel are fixed to the rock layer deep inside the tunnel via rock bolts, thereby stabilizing the rock around the tunnel.

[0068] Cement-based hardeners (mortar, cement milk, etc.) harden slowly over a period of several weeks.

[0069] Furthermore, since concretion using a concretion agent involves sealing by the diffusion of elements, the loosened areas of the rock around the tunnel are densified over a long period of time, such as several months, and this densified rock around the tunnel is fixed to the deeper rock layer via rock bolts, thereby stabilizing the rock around the tunnel (this is the fixing process (S150)).

[0070] 3 is a schematic cross-sectional view showing the structure of the surrounding area of ​​a tunnel reinforced by the method of reinforcing a tunnel deep underground according to the present invention. Note that some of the reference numerals are the same as those in FIG. 13, and their explanation will be omitted.

[0071] Therefore, according to the method for reinforcing tunnels deep underground of the present invention, as shown in Figure 3, the concretion agent penetrates not only the hardened layer g but also the rock mass i around the tunnel in the direction of arrow 20b. This penetration forms concretions, which densify the hardened layer g and the rock mass i around the tunnel. In addition, when loosened portions i of the rock mass around the tunnel located deep underground are fixed to the deep rock mass k using rock bolts 12 and stabilized, a mixture of a cement-based hardener and a concretion agent is used as filler 14 for hole m. As shown by arrow 20a in Figure 3, bicarbonate ions and / or carbonate ions penetrate into the rock mass around the hole (loosened portion i) due to a concentration gradient, and react with calcium ions in the rock mass and groundwater of loosened portion i and calcium ions that have penetrated from the cement-based hardener to precipitate calcium carbonate, which fills the voids and cracks in loosened portion i, thereby improving the loosened portion i to a denser rock structure.

[0072] Naturally, this concretion also occurs in the hole m, and if the concretion agent also contains calcium ions, the calcium ions will penetrate further into the hole m and the rock mass around the hole m, improving the loosened part i to an even denser rock mass structure.

[0073] Furthermore, the densification effect of concretion is maintained for a longer period than with hardened cement, so loosened portions of the rock around the tunnel can be fixed to the deeper rock layer for a longer period than conventional methods.

[0074] Furthermore, the present invention can be implemented by simply mixing a cement-based hardening agent with a concretion agent in a conventional rock bolt construction method, so there is no need to make any major changes to the conventional process.

[0075] Furthermore, as mentioned above, concretion using a concretion agent is not a filling process due to a pressure gradient, but rather a sealing process due to the diffusion of elements, so it can be carried out even in the presence of spring water, and as mentioned above, the voids and cracks in the rock mass around the hole (loosened portion i) are also filled, so the present invention can also prevent spring water from being generated by the formation of a rock bolt hole. This improves the function of the rock mass as a natural barrier, and has a beneficial effect on the safety assessment of radioactive waste disposal projects.

[0076] Furthermore, by installing multiple rock bolts at predetermined intervals on the surface of the tunnel, as in the case of reinforcing a tunnel using conventional rock bolting methods, the rock mass portion (loose portion i) around the tunnel sandwiched between the rock bolts 12, 12 can be effectively densified, as shown in Figure 3.

[0077] Furthermore, since the loosened rock mass around the tunnel can be fixed to the deeper rock layer for a longer period of time than before, the tunnel's lifespan will be extended and the environmental impact of cement production, which accounts for 8% of greenhouse gas emissions, will be reduced. [Example]

[0078] EXAMPLES The present invention will be specifically explained below by showing examples, but the present invention is not limited to these examples.

[0079] (1) Indoor permeability test To confirm the effect of concretion on the loosened area of ​​the rock mass around the tunnel, a laboratory permeability test was carried out using the following procedure.

[0080] 1-1. Creation of test specimen Specimen 1 was prepared by mixing and kneading fine aggregate (land sand), cement (ordinary Portland cement), and water (tap water) in the standard mortar mix for sprayed concrete shown in Table 1 (hereinafter referred to as Mix 1), and Specimen 2 was prepared using the mix used for pit concrete in Table 2, excluding coarse aggregate (hereinafter referred to as Mix 2).

[0081] Specimens 1 and 2 were obtained by mixing and kneading the above mixtures, injecting the mixtures into a mold with a diameter of 100 mm, and curing them underwater for 28 days at room temperature and pressure. -5 ~10 -6 The permeability coefficient of the loosened rock mass around the tunnel is generally smaller than this, but this is to make it easier to confirm the sealing effect on the voids that exist in the rock mass. Specimens 1 and 2 were cut to a thickness of 10 mm, as shown in Figure 4(a).

[0082] [Table 1]

[0083] [Table 2]

[0084] 1-2. Formation of a hardened layer of a mixture of hardener and concretion agent on the test specimen Specimens 1 and 2, each 100 mm in diameter and 10 mm thick (see Figure 4(a)), were embedded in a plastic cup filled with silicone (silicon resin) (product name: G-30M, manufacturer: Shin-Etsu Chemical Co., Ltd.) so that their surfaces were flush with the surface of the silicone, as shown in Figure 4(b), and then left to cure until the silicone solidified.

[0085] Next, 100 parts by mass (mass of solids only, excluding solvent) of epoxy resin (product name: Infraguard (registered trademark) CRJ (main agent / curing agent), manufacturer: Sekisui Chemical Co., Ltd.) as a curing agent, 100 parts by mass of calcium formate (manufactured by Sekisui Chemical Co., Ltd.) and 100 parts by mass of sodium bicarbonate (manufactured by Sekisui Chemical Co., Ltd.) as concretion agents were added to a 5 L polypropylene beaker, and the mixture was stirred to obtain a mixture of curing agent and concretion agent. The actual amounts used are shown in Table 3 below.

[0086] [Table 3]

[0087] As shown in FIG. 5(a), this mixture was poured into a plastic cup so as to be flush with the silicone and each specimen surface, to a thickness of 15 mm (see FIG. 5(b)).

[0088] After the mixture of hardener and concretion agent had hardened, the plastic cup was removed, and the silicone on the back side of each specimen was removed, as shown in Figure 6(a), and two portions of the bottom edge of the silicone were hollowed out to form water channels.

[0089] 1-3.Concrete treatment of specimens The laminates of each specimen manufactured in this way and the hardened layer of hardener and concretion agent were placed in an enamel vat with the hardened layer of hardener and concretion agent facing up, and water (distilled water) was poured into the enamel vat until the hardened layer of hardener and concretion agent was completely submerged (see Figure 6(b)). Each laminate was left in this state and cured underwater at room temperature and pressure for three months, thereby carrying out the concretion treatment of each specimen. Water was periodically poured into the enamel vat during the underwater curing period to maintain a state in which the hardened layer of hardener and concretion agent was completely covered with water.

[0090] 1-4.Evaluation of the hydraulic conductivity of the specimen From the laminate of each test specimen and the hardened layer of hardener and concretion agent, only the hardened layer of hardener and concretion agent was scraped off to obtain test specimens 1-1 and 2-1 that had been subjected to concretion treatment, respectively.

[0091] As controls, specimens 1 and 2 that were not subjected to concretion treatment will be called specimens 1-0 and 2-0.

[0092] Laboratory permeability tests were conducted on specimens 1-1 and 2-1, which had been treated with concretion, and specimens 1-0 and 2-0, which had not been treated with concretion, as follows. Specifically, the tests were conducted in accordance with the Geotechnical Society standard (JGS0312-2018).

[0093] The results are shown in Figure 7, a bar graph showing the hydraulic conductivity (vertical axis: m / s) of specimens 1-1, 2-1, 1-0, and 2-0. As shown in the figure, specimens 1-1 and 2-1, which were densified by concretion treatment, had a significantly lower hydraulic conductivity than specimens 1-0 and 2-0, which were not subjected to concretion treatment.

[0094] (2) X-ray microscope observation test Next, tests were conducted to confirm the effect of the concretion treatment on non-porous, denser general concrete (mortar).

[0095] 2-1. Creation of test specimen A cylindrical hardened mortar body with a diameter of 100 mm and a height of 100 mm was produced using the cement composition (mortar) of Mixture 1 shown in Table 1. The water permeability coefficient of the obtained hardened mortar body was 10 -12 ~10 -11 in the range of m / sec.

[0096] An injection hole 6 (see Figure 8) with a diameter of 36 mm and a depth of 80 mm was drilled in the center of the top surface of this hardened mortar body, downward in the height direction of the hardened mortar body. A mixed liquid of hardener and concretion agent was injected into this injection hole until injection hole 6 was completely filled. The mixed liquid of hardener and concretion agent had the same composition as that used in the above (1) indoor permeability test. The hardened mortar body into which the mixed liquid of hardener and concretion agent had been injected was left to cure in air at room temperature and normal pressure for three months, and a cylindrical specimen 3 shown in Figure 8 was obtained.

[0097] 2-2. X-ray microscope observation Figure 9 is an elemental map of the cross section of the cylindrical specimen 3 taken along line VIII-VIII in Figure 8, created using an X-ray analytical microscope (product name: XGT-5200S, manufacturer: Horiba, Ltd.). The vertical axis indicates calcium concentration, with red indicating areas with high calcium concentration and blue indicating areas with low calcium concentration.

[0098] Furthermore, Figure 10 shows the Ca profile of the area surrounded by the white line in Figure 9. The vertical axis represents the X-ray intensity, and the horizontal axis represents the diameter of the specimen 3, with higher X-ray intensity indicating a greater amount of the element.

[0099] As shown in Figures 9 and 10, it was found that the calcium ions in the concretion agent filled in the injection hole also penetrated into the hardened mortar.

[0100] 2-3.Evaluation As mentioned above, the permeability coefficient of standard mortar is 10 -12 ~10 -11 As the permeability of the concrete is at the level of m / sec, and it is difficult to confirm its effect in an indoor water permeability test, as with porous mortar, the effect of concretions in standard mortar was visually verified by the X-ray microscope observation test described above (2). As a result, it was confirmed that calcium ions penetrated the standard mortar as well, just like porous mortar.

[0101] Therefore, it was shown that the concretion agent can penetrate into the hardened layer of cement composition sprayed onto the surface of a tunnel located deep underground and into the surface layer of the tunnel, including loosened areas including porous portions, causing concretion.

[0102] The inventors have also confirmed the migration of the concretion agent into porous mortar and standard mortar and the concretion formation effect when a cement-based hardener (mortar) is used instead of a resin-based hardener.

[0103] (3) Elemental analysis by EPMA Next, in order to confirm whether the concretion effect can be obtained on porous rock, following the porous mortar and standard mortar, a test was conducted to confirm the effect of concretion on rock (tuff).

[0104] A disk-shaped pumice tuff with a diameter of 50 mm and a height of 10 mm (collected by a backhoe at an excavation site within the Rokkasho Mura site of Japan Nuclear Fuel Co., Ltd., wet density 1.26 mg / m 3 As with the mortar specimens, a mixture of the hardener and concretion agent shown in Table 3 was applied to the surface of the mortar specimen to a thickness of 15 mm, and the mixture was then cured in water for three months. From the resulting laminate of the disk-shaped pumice tuff and the hardened layer of hardener and concretion agent, only the hardened layer of hardener and concretion agent was scraped off to obtain specimen 3-1.

[0105] Figure 11 is a plan view of specimen 3-1. As shown in the figure, specimen 3-1 was cut in its height direction at the location of line AA, and elemental mapping of the cut surface of specimen 3-1 was performed using an electron probe microanalyzer or electron probe microanalyzer (EPMA). In this test, a JXA-8230 electron probe microanalyzer (manufactured by JEOL Ltd.) was used as the EPMA.

[0106] Figure 12(a) is a photograph (substitute for a drawing) showing the results of elemental mapping of the cut surface of specimen 3-1, and Figure 12(b) is a photograph (substitute for a drawing) showing the results of elemental mapping of the cut surface of a disk-shaped pumice tuff (hereinafter referred to as specimen 3-0) to which the mixture of hardener and concretion agent had not been applied.

[0107] As shown in the figure, Ca (the red part that appears white) is only distributed locally in specimen 3-0, whereas in specimen 3-1, Ca is distributed across the entire cross section from the front to the back, indicating that concretions have occurred even inside the pumice tuff.

Claims

1. A cement composition for spray application to the surface of a tunnel provided deep underground to reinforce the tunnel, A cement composition for spray application onto tunnel surfaces, comprising cement, aggregate, a concreting agent, and water.

2. 2. The cement composition for spray application onto tunnel surfaces according to claim 1, wherein the concretion agent comprises sodium bicarbonate and a calcium ion source.

3. 2. The cement composition for spray application onto tunnel surfaces according to claim 1, wherein the tunnel is a tunnel for storing radioactive waste.

4. A method for reinforcing a tunnel deep underground, comprising a hardened layer forming step of spraying the cement composition according to any one of claims 1 to 3 into a tunnel provided deep underground to obtain a hardened layer of the cement composition.

5. Furthermore, a hole forming step of forming a hole from the surface of the hardened layer of the cement composition in the tunnel to a bedrock layer deep in the tunnel; a lock bolt insertion step of inserting a lock bolt into the hole; an injection step of injecting a mixture of a cement-based hardener and a concretion agent into the hole before or after the rock bolt insertion step; a fixing process in which the cement-based hardener is hardened, and the loosened area of ​​the rock mass around the tunnel is fixed to the rock layer deep in the tunnel via rock bolts, thereby stabilizing the rock mass around the tunnel; 5. The method for reinforcing a tunnel deep underground according to claim 4, further comprising:

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