Ground reinforcement method for utilizing existing underground structures as underground shelters

Abstract

To provide a method for reinforcing an existing underground structure by using a chemical grouting method, which can reinforce an existing underground shelter and can also reinforce an existing underground structure so that it can be effectively used as an underground shelter. [Solution] The method of reinforcing an existing underground structure 11 according to the present invention is characterized in that the ground 1 around the periphery of the existing underground structure 11 is improved by a chemical grouting method, reducing the degree of saturation of the ground 1 and making it unsaturated, thereby constructing a buffer 12 around the periphery of the existing underground structure 11 and attenuating external energy. Also, if the existing underground structure 11 is an existing underground shelter, the buffer 12 made of reinforced ground can be formed around the periphery of the underground shelter by chemical grouting, thereby improving the durability, strength, and safety of the underground shelter against, for example, incoming ballistic missiles.

Description

[Technical field]

[0001] The present invention relates to a method for reinforcing an existing underground structure, which attenuates the blast pressure caused by, for example, an incoming ballistic missile by desaturating the ground, and which reinforces an existing underground shelter by a chemical injection method, and which reinforces an existing underground structure to effectively utilize it as an underground shelter. [Background technology]

[0002] During Russia's invasion of Ukraine, many Ukrainian citizens took refuge in basements of buildings and subways. In particular, subways are built deep in preparation for a nuclear attack. Meanwhile, in Japan, the Civil Protection Act of 2004 required local governments to designate shelters, but as of 2023, only about 12,000 of the approximately 50,000 designated evacuation facilities were underground.

[0003] By positioning a wide range of existing underground facilities as shelters, it seems possible to effectively utilize them as underground shelters to escape to in the event of a ballistic missile attack. However, since some of the country's subways are built at a relatively shallow depth, reinforcement against the explosive energy of a missile is necessary, but effective means for this have not yet been considered.

[0004] Patent Document 1 discloses a radiation shielding material that is characterized by using asphalt in the form of powder, pellets, or blocks and / or molded panels or plates as a material for shielding radiation.

[0005] Patent Document 2 discloses a radiation shielding device which uses tungsten, a tungsten compound, or a tungsten-based alloy, or a mixture with other heavy metals (hereinafter referred to as "tungsten, etc.") as a material with a high radiation shielding rate, and mixes a film-forming material 6 with shielding particles 1 made of "tungsten, etc." to form a mixed shielding material 7, which is integrated with a cloth body 8 made of natural fibers such as cotton, linen, or silk, and / or synthetic fibers, and / or nonwoven fabric, and / or paper, etc., by a coating means such as coating, pasting, baking, or printing, to form a shielding cloth 9, and which is connected to another piece of shielding cloth 9 by a connecting means 11 such as adhesion, welding, sewing, button fastening, or hook-and-loop fastener to form radiation shielding members 12 of various shapes.

[0006] Patent Document 3 discloses a container having an interior structure made of a material that prevents radiation leakage.

[0007] Patent Documents 4, 5, 6, and 7 are by the present applicant, and Patent Document 4 discloses a durable silica grout and a durable silica ground improvement method using the durable silica grout. The durable ground injection grout and durable ground injection method use a non-alkaline silica grout containing silica sol, silica colloid, or water glass as an active ingredient.

[0008] Patent Document 5 discloses a ground injection material used in a ground injection method in which fine particles are injected into the ground to increase its density and solidify it at the same time, the ground injection material being characterized in that it is made of blast furnace slag as a main ingredient to which gypsum or magnesium oxide, or both, are added as active ingredients as reactants, and the pH of the ground injection material is adjusted to be 8 to 12.

[0009] Patent Document 6 describes a liquefaction countermeasure method that uses silica grout containing microbubbles, a technology in which improvement effects are achieved by the contraction of fine bubbles in response to shear stress.

[0010] Patent Document 7 shows a method for improving the quality of the technology described in Patent Document 6 by using microbubbles in combination with silica grout containing microbubbles. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] JP 2016-206055 A [Patent Document 2] JP 2013-044737 A [Patent Document 3] JP 2013-127439 A [Patent Document 4] Patent No. 6460432 [Patent Document 5] Patent No. 7193105 [Patent Document 6] Patent No. 5158390 [Patent Document 7] Patent No. 5433885 [Patent Document 8] Patent No. 6792117 [Non-patent literature]

[0012] [Non-Patent Document 1] Akio Yamaji, Shigeo Numata, Tetsuo Saito, "Design method of compensating shielding incorporated into a concrete wall for gamma ray shielding with a straight duct and measurement and analysis of dose rate distribution", Journal of the Atomic Energy Society of Japan, Vol. 29, No. 6, pp. 77-85, 1987. [Non-Patent Document 2] Takashi Sekine, "Radiation Shielding", July 1970, RADIOISOTOPES, Vol. 19, No. 7, pp. 48-58 [Non-Patent Document 3] Takamitsu Sasaki, Ryozo Yonekura, Shunsuke Shimada, "Field verification test of age-related consolidation of consolidated ground using activated silica and ultrafine silica composite", 54th Geotechnical Engineering Research Conference, 2019, 0241, pp.481-482 [Non-Patent Document 4] Daisuke Muto, "On the magnitude of earthquakes caused by explosions or collisions," Seismic Research Journal, Vol. 81, pp. 1-6, 2017. [Non-Patent Document 5] Katsumi Tanaka, "Analysis of Explosion Phenomena", Safety Engineering, Vol. 36, No. 6, pp. 383-389, 1997. [Non-Patent Document 6] Takamitsu Sasaki, Naoaki Suemasa, Shunsuke Shimada, "Study on the strength development mechanism of soil improved by grouting using elastic wave testing", Journal of Japan Society of Civil Engineers, Vol. 76, No. 4, pp. 374-393, 2020. [Non-Patent Document 7] Hiroyoshi Ichino, Tomonori Ohno, Masahiro Beppu, Kazuo Hasue, "Effects of Grain Size and Saturation of Soil on Earth Pressure Characteristics in Underground Explosions of Explosives", Journal of Japan Society of Civil Engineers, Vol. 64, No. 2, pp. 353-368 [Non-Patent Document 8] Kenji Yonezawa, Yoshihide Suwa, Yoshiyuki Ono, Yoichi Naganuma, "Experimental Study on Response Characteristics of RC Walls Subjected to Hydrogen Blast Pressure", Journal of Structural Engineering, Architectural Institute of Japan, No. 601, pp. 151-158 Summary of the Invention [Problem to be solved by the invention]

[0013] In recent years, subways, underground shopping malls, tunnels, etc. have been considered as shelters from the perspective of national defense, but they were not built with such events in mind, and some of them have since deteriorated over time, causing a decrease in strength and water leakage from joints, so there is a need to strengthen underground concrete structures.

[0014] In particular, many subway tunnels are constructed using the shield method, and their segments use ordinary cement concrete with a thickness of about 75mm to 225mm. On the other hand, if they are expected to function as shelters against nuclear weapons, the concrete used should be high-density heavy concrete containing barite and magnetite, and it is thought that a thickness of about 150mm to 400mm is required. Therefore, it is not possible to expect existing subway tunnels to function as nuclear shelters (Non-Patent Documents 1 and 2).

[0015] Ground improvement methods are used in earthquake-resistance reinforcement works against earthquake motion. The principles of these methods include compaction, solidification, and shear deformation control. Compaction methods are prone to horizontal and vertical stress and displacement, making them difficult to apply to existing structures. In addition, while methods that prevent shear deformation can be carried out near existing structures in some cases, they are often difficult to apply in urban areas with many underground structures, and especially in the ground surrounding subway shields.

[0016] On the other hand, among the methods that rely on solidification, mechanical mixing methods are difficult to carry out when underground objects are present, and high-pressure jet mixing methods can have an adverse effect on underground objects as well as problems with sludge disposal. [Means for solving the problem]

[0017] Existing underground structure according to the present invention The foundation for using it as an underground shelter The reinforcement method involves carrying out ground improvement work on the ground around the existing underground structure using a chemical injection method. A ground reinforcement method for utilizing an existing underground structure as an underground shelter, comprising the steps of: using microbubble water or silica grout containing microbubbles as an injection material in the chemical injection method; By lowering the saturation level of the ground and making it unsaturated, a buffer is constructed around the periphery of the existing underground structure, attenuating the energy acting from the outside. The range and strength of the buffer body are designed to be strong and have a range that can withstand the explosive energy of a predicted ballistic missile. It is characterized by the above.

[0018] In addition, the existing underground structure of the present invention The foundation for using it as an underground shelter In the reinforcement method, the injection material used in the chemical injection method As Microbubbles Water or silica grout containing microbubbles is used. It is preferable that

[0019] The present invention relates to improving the ground around an existing underground structure by a chemical grouting method, which is one of the solidification methods, and the conditions suitable for such purpose are set as follows. 1) The injection material used shall be silica grout containing microbubbles, or a combination of microbubbles and silica grout containing microbubbles, or a combination of microbubbles and silica grout (hereinafter referred to as unsaturated grout). 2) Desaturation reduces the earth pressure caused by explosion energy through a damping effect. 3) Excellent permeability during construction and water-stopping properties as an improvement effect. 4) If functionality against nuclear bombs is expected, the injection material must have a radiation shielding effect. 5) Low carbon injection materials and injection methods are desirable.

[0020] Existing underground structure of the present invention The foundation for using it as an underground shelter In the reinforcement method, the radiation shielding function can be enhanced by using an injection material containing a clay-based radiation shielding material as the injection material.

[0021] The applicant has already developed Patent Documents 4 and 5 as permanent grouts that can be expected to have long-term durability, and has demonstrated the sustainability of their improvement effects (Non-Patent Document 3). For example, the solution-type grout described in Patent Document 4 has high permeability.

[0022] In addition, the suspension-type grout described in Patent Document 5 has a solidification mechanism similar to that of cement, so it is injected into the ground around the periphery of an existing underground structure, and the buffer formed by the reinforced ground around the periphery of the existing underground structure is expected to be strong and provide radiation shielding. In addition, since the main agent of the suspension-type grout is slag, it can be said to be a low-carbon grout because of its low carbon dioxide emission intensity.

[0023] Existing underground structure of the present invention The foundation for using it as an underground shelter In the reinforcement method, A suspension grouting material is injected into the outer periphery of the existing underground structure to form a reinforcement body, and the buffer body is constructed on the outer periphery of the reinforcement body. It may be arranged to do so.

[0024] Existing underground structure according to the present invention The foundation for using it as an underground shelter The reinforcement method uses the inventions described in Patent Documents 6 and 7 to form a buffer body by desaturation around the periphery of an existing underground structure, thereby attenuating external energy and enabling the existing underground structure to be effectively used as an underground shelter. Therefore, the inventions described in Patent Documents 6 and 7 have the effect of suppressing the rise in excess pore water pressure by shrinking air bubbles in response to repeated shear stress caused by earthquake motion, thereby preventing liquefaction, which is different from the purpose and improvement principle of this invention.

[0025] In the method for reinforcing an existing underground structure according to the present invention, the existing underground structure may be an existing underground shelter. The unsaturated grout in the method for reinforcing an existing underground structure according to the present invention can reduce earth blast pressure generated in the existing underground shelter.

[0026] Existing underground structure of the present invention The foundation for using it as an underground shelter In the reinforcement method, the extent and strength of the buffer can be designed to be strong and to have an extent that can withstand the potential explosive energy of a ballistic missile.

[0027] In the present invention, a buffer body formed on the outer periphery of an existing underground structure using unsaturated grout can attenuate the earth blast pressure of an incoming ballistic missile and improve the earthquake resistance of existing underground shelters. However, if the earth blast pressure cannot be attenuated sufficiently, a method of reinforcing the existing underground structure can be used to reinforce the ground between the buffer body and the structure using the invention described in Patent Document 5, and the structure can be designed to have the strength and range to withstand the explosive energy of anticipated ballistic missiles, etc.

[0028] In addition, the existing underground structure of the present invention The foundation for using it as an underground shelter In the reinforcement method, the explosion energy may be converted into seismic energy to calculate the range and strength of the buffer.

[0029] In addition, the existing underground structure of the present invention The foundation for using it as an underground shelter In the reinforcement method, the explosion energy may be converted into an explosion earth pressure to calculate the range and strength of the buffer body.

[0030] In addition, the existing underground structure according to the present invention The foundation for using it as an underground shelter In the reinforcement method, the explosive energy of a ballistic missile, etc. can be converted into earth blast pressure to calculate the range of the buffer body and the range and strength of the ground reinforcement according to the invention described in Patent Document 5. Effect of the Invention

[0031] The present invention can reduce the earth blast pressure acting on underground structures, allowing existing underground structures to be effectively used as underground shelters. In particular, by using the present invention in combination with a suspension grouting material, it is possible to further improve impact resistance. [Brief description of the drawings]

[0032] [Figure 1] FIG. 1 is a schematic diagram showing an embodiment of a method for reinforcing an existing underground structure using silica grout containing microbubbles, which is an example of the method for reinforcing an existing underground structure of the present invention when a buried pipe is located near the existing underground structure. [Diagram 2] FIG. 1 is a schematic diagram showing the combined use of microbubbles and silica grout in the method for reinforcing an existing underground structure of the present invention. [Diagram 3] FIG. 1 is a schematic diagram showing an embodiment of the present invention in which the effect of reducing earth blast pressure by silica grout containing microbubbles and the reinforcement of an existing underground structure by suspension grout are combined. [Figure 4] 1 is a graph showing the relationship between the B value and unconfined compressive strength and elastic wave velocity. [Diagram 5] 1 is a graph showing the effect of the degree of saturation Sr on the relationship between blast earth pressure and distance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0033] Hereinafter, embodiments of the present invention will be described in detail with reference to tables and drawings. Note that the present invention is not limited to the embodiments described below.

[0034] Fig. 1 is a schematic diagram showing one embodiment of the method of reinforcing an existing underground structure 11 of the present invention. The existing underground structure 11 is located in the ground 1, and an access passage 14 is provided on the side of the existing underground structure 11, connecting the ground to the existing underground structure 11. In addition, buried objects 2 such as water pipes and gas pipes exist in the shallow part of the existing underground structure 11, making it difficult to drill holes from the ground surface and install injection pipes.

[0035] Therefore, an injection pipe 13 is inserted from inside the existing underground structure 11 toward the ground 1, and silica grout containing microbubbles is injected into the circumferential surface of the existing underground structure 11 to form a buffer body 12. An injection pipe 13 is also inserted into the side of the access passage 14 to inject the chemical solution and form a buffer body 12. By solidifying in an unsaturated state, it is possible to attenuate energy acting from the outside.

[0036] 2 is a schematic diagram showing a case where there is no buried pipe near the existing underground structure 21. An access passage 25 that connects the ground to the existing underground structure 21 is provided on the side of the existing underground structure 21. In this case, a hole is drilled from the ground surface, and an injection pipe 24 can be installed.

[0037] Microbubble water is injected near the existing underground structure 21 and desaturated to form a buffer body 22. Microbubble water is also injected into the side of the access passage 25. After confirming that the saturation level has decreased to a predetermined level, a water barrier 23 made of silica grout containing microbubbles or silica grout is constructed to prevent the advection and diffusion of the microbubble water.

[0038] This is because the formation of the buffer body 22 by desaturation and the construction of the water impermeable wall 23 are separate processes, making it possible to achieve a low degree of saturation and reliable desaturation.

[0039] Fig. 3 is a schematic diagram showing a case where there is no buried pipe near the existing underground structure 31, assuming a condition of high earth blast pressure. An access passage 35 is provided on the side of the existing underground structure 31, connecting the ground to the existing underground structure 31. In this case, a hole is drilled from the ground surface, and an injection pipe 34 can be installed.

[0040] When a missile lands near an existing underground structure 31 or when a missile with a large amount of explosives is launched, there is a possibility that the desaturation by microbubbles alone will not be effective enough to attenuate the earth blast pressure. In such a case, suspension grout can be injected along the existing underground structure 31 to increase the apparent wall thickness, thereby making it possible to withstand the impact of earth blast pressure. In FIG. 3, a reinforcing body 32 made of suspension grout is formed along the periphery of the existing underground structure 31, and a buffer body 33 made of silica grout containing microbubbles is constructed on the outside of the reinforcing body 32.

[0041] In addition, the existing underground structure in the present invention may be, for example, a structure installed in the ground, such as a tunnel, a subway station, an underground shopping mall, an underground passage, etc. In addition, by forming a buffer body on the outer periphery of a structure originally installed as an underground shelter, the performance as an underground shelter can be improved.

[0042] The injection materials used in the method of reinforcing an existing underground structure of the present invention are microbubbles or silica grout containing microbubbles for use in constructing a buffer body, silica grout for constructing a water barrier to prevent the advection and diffusion of air bubbles, and suspension grout for improving impact resistance against earth blast pressure. It is preferable to use a solution-type injection material or suspension-type injection material that the applicant has already developed as a permanent grout that can be expected to have long-term durability and has demonstrated the sustainability of its ground improvement effects.

[0043] In the method of reinforcing existing underground structures according to the present invention, the range of the buffer body created by desaturation and the injection range and strength of the suspension-type grouting material for reinforcement purposes are designed so as to withstand the blast earth pressure caused by the anticipated explosive energy of a ballistic missile.

[0044] The design involves converting the amount of explosive into trinitrotoluene (TNT) based on the type of missile and the amount of explosive assumed, and then using this and the distance from the impact point to the underground structure, calculate the blast pressure using Equation 1 (Non-Patent Document 7).

[0045]

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[0046]

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[0047]

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[0048]

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[0049] Next, the resistance of the underground structure to the obtained blast earth pressure is verified. Although FEM analysis is an effective verification method, a simple method is to consider the degree of damage based on the wall thickness and blast pressure shown in Table 1, which is the experimental results on blast pressure and damage to reinforced concrete described in Non-Patent Document 8.

[0050] [Table 1]

[0051] If, as a result of examining the blast earth pressure and the resistance capacity of the underground structure, it is determined that there is a risk of damage to the underground structure, a buffer body will be constructed by desaturating the ground to reduce the blast earth pressure.

[0052] If the explosive earth pressure acting on an underground structure is still great even after constructing a buffer body by desaturating the ground, a suspension grouting material is injected into the ground adjacent to the underground structure to increase the apparent wall thickness of the structure.

[0053] When the ground is made unsaturated, it has the characteristic of decreasing the longitudinal elastic waves, as shown in Figure 3. Using this characteristic, the invention described in Patent Document 8 is effective as a method for confirming the quality of improved ground, and can also be utilized in this patented technology.

[0054] Example 1 Here, we present an example of the study under the following conditions. The calculation was performed assuming that the missile weighs 1,000 kg of TNT and will land 30 m away from an underground structure with a wall thickness of 100 mm. The target ground is sandy soil and is saturated.

[0055] The blast pressure calculated from formula 1 is about 260 kPa, as shown in Figure 4. It is generally believed that concrete structures will suffer some damage if the blast pressure exceeds 100 kPa. This possibility can also be seen in Table 1.

[0056] Microbubbles are injected around the structure and the saturation level S r By reducing the pressure to 80%, the earth blast pressure can be reduced to 50 kPa or less, as shown in Fig. 4, and the soundness of the concrete can be maintained.

[0057] Example 2 Here, we present an example of the study under the following conditions. The calculation was performed assuming that the missile weighs 2000kg of TNT and will land 30m away from an underground structure with a wall thickness of 100mm. The target ground is sandy soil and is saturated.

[0058] The blast pressure calculated from Equation 1 is approximately 400 kPa, as shown in Figure 4, which will definitely cause damage to the concrete structure.

[0059] Microbubbles are injected around the structure and the saturation level S r If the pressure is reduced to 80%, the earth blast pressure can be reduced to 100 kPa or less, as shown in Fig. 4, but damage to the concrete may occur.

[0060] In such cases, as shown in Figure 3, a suspension grout is injected around the underground structure to increase the apparent wall thickness and ensure cross-sectional rigidity. The minimum improvement thickness is preferably about 0.5 m to ensure the continuity of the improved body.

[0061] The required thickness of the suspension grout is calculated by the uniaxial compressive strength q of the suspension grout. u is 1 to 10MN / m 2 Deformation coefficient E is 0.1 to 2.0GN / m 2 This is about 1 / 20 to 1 / 40 of that of concrete. Therefore, the minimum improvement range is determined by FEM analysis using these minimum values, and compared with the minimum improvement thickness. [Explanation of symbols]

[0062] 1...Ground 2... Buried objects (water and sewer pipes, gas pipes, etc.) 11...Existing underground structures 12...Improvement using silica grout containing microbubbles (buffer) 13...Injection tube 14…Access passage 21...Existing underground structure 22…Microbubble cushioning 23...Waterproof wall using silica grout 24...Injection tube 25…Access passage 31...Existing underground structure 32...Reinforcement of existing underground structures using suspended grout 33...Buffer made of silica grout containing microbubbles 34...Injection tube 35…Access passage

Claims

1. A ground reinforcement method for utilizing an existing underground structure as an underground shelter by carrying out ground improvement work on the ground around the periphery of the existing underground structure using a chemical injection method, the method comprising the steps of: using microbubble water or silica grout containing microbubbles as an injection material for the chemical injection method; reducing the saturation level of the ground and making it unsaturated, thereby constructing a buffer body around the periphery of the existing underground structure and attenuating energy acting from the outside; and designing the range and strength of the buffer body to be strong and within a range that can withstand the explosive energy of an anticipated ballistic missile.

2. 2. A ground reinforcement method for utilizing an existing underground structure as an underground shelter, as described in claim 1, characterized in that the injection material further contains a radiation shielding material mainly made of clay.

3. A ground reinforcement method for utilizing an existing underground structure as an underground shelter, as described in claim 1 or 2, characterized in that a suspension-type injection material is injected into the outer periphery of the existing underground structure to form a reinforcing body, and the buffer body is constructed on the outer periphery of the reinforcing body.

4. A ground reinforcement method for utilizing an existing underground structure as an underground shelter, comprising the steps of: injecting microbubble water into the outer periphery of the existing underground structure to construct the buffer body; and injecting silica grout containing microbubbles or silica grout into the outer periphery of the buffer body to construct a watertight wall.

5. 2. A ground reinforcement method for utilizing an existing underground structure as an underground shelter, as described in claim 1, characterized in that the explosion energy is converted into earthquake energy to calculate the range and strength of the buffer body.

6. 2. A ground reinforcement method for utilizing an existing underground structure as an underground shelter, comprising the steps of: converting the explosion energy into blast earth pressure to calculate the range and strength of the buffer body;

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