Ground reinforcement method for utilizing existing underground structures as underground shelters

Abstract

This invention provides a method for reinforcing existing underground shelters and existing underground structures using chemical grout injection, enabling their effective use as underground shelters. [Solution] The method for reinforcing an existing underground structure 11 according to the present invention is characterized by performing ground improvement using a chemical grout injection method on the ground 1 on the outer perimeter of the existing underground structure 11, thereby reducing the saturation of the ground 1 and making it unsaturated, and constructing a buffer body 12 on the outer perimeter of the existing underground structure 11, thereby attenuating energy acting from the outside. Furthermore, if the existing underground structure 11 is an existing underground shelter, a buffer body 12 made of reinforced ground can be formed on the outer perimeter of the underground shelter by chemical grout injection, 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 existing underground structures, which, for example, attenuates blast pressure caused by incoming ballistic missiles by desaturating the ground, and also reinforces existing underground shelters and existing underground structures using a chemical grouting method to effectively utilize them as underground shelters. [Background technology]

[0002] During Russia's invasion of Ukraine, many Ukrainian citizens took refuge in building basements or subway stations. The subway, in particular, is built at great depths to prepare for a nuclear attack. In contrast, in Japan, while the National Protection Law enacted in 2004 mandated that local governments designate shelters, as of 2023, only about 12,000 of the approximately 50,000 designated shelters were underground facilities.

[0003] By broadly designating existing underground facilities as shelters, they could be effectively utilized as underground refuges to take refuge in the event of a ballistic missile attack. However, some of Japan's subways are built at relatively shallow depths, so reinforcement against the explosive energy of missiles is necessary, but effective means of doing so have not yet been considered.

[0004] Patent Document 1 discloses a radioactive shielding material characterized by using powdered, pelletized, or lumpy asphalt and / or molded panel-shaped or plate-shaped asphalt as a material for shielding against radioactivity.

[0005] Patent Document 2 discloses a radiation shielding device characterized by using 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, mixing a film-forming material 6 with shielding particles 1 made of "tungsten, etc." to form a mixed shielding material 7, which is then integrated into a shielding cloth 9 by coating, attaching, baking, or printing on a cloth body 8 made of natural fibers such as cotton, linen, or silk, and / or synthetic fibers, and / or nonwoven fabrics, and / or paper, etc., using coating means such as coating, attaching, baking, or printing, and joining the shielding cloth 9 and another piece of shielding cloth 9 by bonding means 11 such as adhesive, welding, sewing, button fastening, or hook-and-loop fasteners to form radiation shielding members 12 of various shapes.

[0006] Patent Document 3 discloses a container having a structure lined with a material that prevents radioactive leakage.

[0007] Patent documents 4, 5, 6, and 7 are by the present applicant, and Patent document 4 discloses durable silica grout and a durable silica ground improvement method using durable silica grout. It is a durable ground injection grout and durable ground injection method using non-alkaline silica grout with silica sol, silica colloid, or water glass as active ingredients.

[0008] Patent Document 5 discloses a ground injection material used in a ground injection method that involves injecting fine particles into the ground to increase density and solidify it, characterized in that it is mainly composed of blast furnace slag, to which gypsum, magnesium oxide, or both are added as active ingredients as a reactant, and the pH of the ground injection material is set to 8 to 12.

[0009] Patent document 6 describes a liquefaction countermeasure method using silica grout containing microbubbles, in which the improvement effect is achieved by the contraction of fine bubbles in response to shear stress.

[0010] Patent Document 7 describes a method for improving the quality of the technology described in Patent Document 6, which involves the combined use of microbubbles and silica grout containing microbubbles. [Prior art documents] [Patent Documents]

[0011] [Patent Document 1] Japanese Patent Publication No. 2016-206055 [Patent Document 2] Japanese Patent Publication No. 2013-044737 [Patent Document 3] Japanese Patent Publication No. 2013-127439 [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, and Tetsuo Saito, "Design Method and Measurement and Analysis of Dose Rate Distribution of Compensating Shielding Components Incorporated into Concrete Walls for Gamma Ray Shielding with Straight Ducts," 1987, Journal of the Atomic Energy Society of Japan, Vol. 29, No. 6, pp. 77-85. [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, and Shunsuke Shimada, "Field Demonstration Test of Long-Term Consolidation Properties of Consolidated Ground Using Activated Silica and Ultrafine Particle Composite Silica," 2019, Proceedings of the 54th Japanese Geotechnical Society, 0241, pp. 481-482. [Non-Patent Document 4] Daisuke Muto, "Regarding the Magnitude of Earthquakes Generated by Explosions or Collisions", 2017, Earthquake Observation Report, Vol. 81, pp. 1-6 [Non-Patent Document 5] Katsumi Tanaka, "Analysis of Explosion Phenomena", 1997, Safety Engineering, Vol. 36, No. 6, pp. 383-389 [Non-Patent Document 6] Takamitsu Sasaki, Naoki Sue政, Shunsuke Shimada, "Examination of the Strength Development Mechanism of Improved Soil by Chemical Solution Injection Materials Using Elastic Wave Tests", Journal of the Japan Society of Civil Engineers, Series C (Geotechnical Engineering), Vol. 76, No. 4, pp. 374-393, 2020. [Non-Patent Document 7] Hiroyoshi Ichino, Tomonori Ohno, Manabu Befu, Kazuo Hasue, "Influence of Soil Particle Size Composition and Saturation on Explosion Soil Pressure Characteristics in Underground Explosions of Explosives", Journal of the Japan Society of Civil Engineers, Series C, Vol. 64, No. 2, pp. 353-368 [Non-Patent Document 8] Kenji Yonezawa, Yoshihide Suwa, Yoshiyuki Ono, Yoichi Naganao, "Experimental Study on the Response Behavior of RC Walls Subjected to Hydrogen Blast Pressure", Transactions of the Japan Society of Civil Engineers, Structural Engineering Division, No. 601, pp. 151-158 [Summary of the Invention] [Problems to be Solved by the Invention]

[0013] In recent years, from a national defense perspective, subways, underground shopping malls, tunnels, etc. have been considered as shelters, but these were not constructed assuming such situations, and furthermore, in some cases, strength degradation due to aging deterioration and water leakage from joints have occurred, so it is necessary to strengthen underground concrete structures.

[0014] In particular, many subways are constructed by the shield method. The segments usually use ordinary cement concrete, and their thickness is about 75 mm to 225 mm. On the other hand, when expecting to function as a shelter against nuclear weapons, the concrete to be used is high-density heavy concrete containing baryte and magnetite, and a thickness of about 150 mm to 400 mm is considered necessary. Therefore, it is impossible to expect the function of a nuclear shelter in existing subway tunnels (Non-Patent Documents 1 and 2).

[0015] In earthquake-resistant reinforcement work against seismic motion, there are ground improvement methods. Their principles include compaction, solidification, and shear deformation suppression. Compaction methods are difficult to apply to existing structures because horizontal and vertical stresses and displacements are likely to occur. Also, those based on shear displacement suppression may be applicable in some cases near existing structures, but they are often difficult to apply in urban areas with many underground buried objects, especially in the surrounding ground of subway shields. <00001​​​​​​​​​​​​​​​​​This invention provides a method for improving the ground surrounding existing underground structures using a chemical grout injection method, which is one of the solidification methods. The conditions suitable for this purpose are set as follows. 1) The grout 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) By desaturating the soil, the blast pressure caused by the explosion energy is reduced through a damping effect. 3) Excellent permeability during construction and water-stopping properties as an improvement effect. 4) If expected to function against nuclear bombs, the injectable material must have a radiation shielding effect. 5) Low-carbon injection materials and injection methods are preferable.

[0020] In the method for reinforcing existing underground structures according to the present invention, the radiation shielding function can also be enhanced by using an injection material to which a radiation shielding material mainly composed of clay is added as the injection material.

[0021] The applicant has already developed permanent grout materials with long-term durability as described in Patent Documents 4 and 5, and has demonstrated the sustainability of their improved effects (Non-Patent Document 3). For example, the solution-type grout material described in Patent Document 4 has high permeability.

[0022] Furthermore, the suspension-type injection material described in Patent Document 5 has a solidification mechanism similar to that of cement, so when injected into the ground around the perimeter of an existing underground structure, the buffer formed by the reinforced ground around the perimeter of the existing underground structure is expected to be highly strong and provide radiation shielding. Moreover, since the main component of the suspension-type injection material is slag, it can be considered a low-carbon injection material due to its low carbon dioxide emission intensity.

[0023] In the method for reinforcing an existing underground structure according to the present invention, a reinforcing body may be formed by injecting a suspension-type injection material into the inside of the buffer body before constructing the buffer body.

[0024] The method for reinforcing existing underground structures according to the present invention utilizes the inventions described in Patent Documents 6 and 7 to form a buffer body on the outer periphery of the existing underground structure by desaturation, thereby attenuating externally acting energy and enabling the existing underground structure to be effectively utilized 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 the contraction of air bubbles in response to repeated shear stress caused by seismic motion, thereby preventing liquefaction, and are different from the objective and improved principle of the present invention.

[0025] Furthermore, 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 the blast pressure generated in the existing underground shelter.

[0026] In the method for reinforcing existing underground structures according to the present invention, the range and strength of the buffer can be designed to have strength and range that can withstand the explosive energy of an anticipated ballistic missile.

[0027] In this invention, a buffer formed on the outer perimeter of an existing underground structure using unsaturated grout can reduce the blast pressure of incoming ballistic missiles, thereby improving the seismic resistance of existing underground shelters. However, if the blast pressure cannot be sufficiently reduced, as a method of reinforcing the existing underground structure, ground reinforcement using the invention described in Patent Document 5 can be performed between the buffer and the structure, and the reinforcement can be designed to have sufficient strength and range to withstand the explosive energy of anticipated ballistic missiles.

[0028] Furthermore, in the method for reinforcing existing underground structures according to the present invention, the range and strength of the buffer may be calculated by converting the explosion energy into seismic energy.

[0029] Furthermore, in the method for reinforcing existing underground structures according to the present invention, the range and strength of the buffer body may be calculated by converting the explosion energy into blast pressure.

[0030] Furthermore, in the method for reinforcing existing underground structures according to the present invention, the explosive energy of ballistic missiles and the like can be converted into blast pressure to calculate the range of the buffer and the range and strength of the ground reinforcement according to the invention described in Patent Document 5. [Effects of the Invention]

[0031] This invention makes it possible to reduce the blast pressure acting on underground structures, thereby enabling the effective use of existing underground structures as underground shelters. In particular, by using a suspension-type injection material in combination, it is possible to further improve impact resistance. [Brief explanation of the drawing]

[0032] [Figure 1] This is a schematic diagram illustrating one embodiment of the method for reinforcing existing underground structures according to the present invention, specifically when there are buried pipes near the existing underground structure, and using silica grout containing microbubbles. [Figure 2] This is a schematic diagram illustrating the method for reinforcing existing underground structures according to the present invention, which uses microbubbles and silica grout in combination. [Figure 3] This is a schematic diagram illustrating one embodiment of the present invention that combines the effect of reducing blast pressure by silica grout containing microbubbles with the reinforcement of existing underground structures by suspension-type grout. [Figure 4] This graph shows the relationship between the B value, uniaxial compressive strength, and elastic wave velocity. [Figure 5] This graph shows the effect of saturation level (Sr) on the relationship between blast pressure and distance. [Modes for carrying out the invention]

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

[0034] Figure 1 is a schematic diagram showing one embodiment of the method for reinforcing an existing underground structure 11 according to the present invention. An existing underground structure 11 is located in the ground 1, and an access passage 14 connecting the ground surface to the existing underground structure 11 is provided on the side of the existing underground structure 11. Furthermore, since there are buried objects 2 such as water pipes and gas pipes in the shallow part of the existing underground structure 11, it is difficult to drill from the ground surface and install injection pipes.

[0035] Therefore, an injection pipe 13 is inserted from within 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. In addition, an injection pipe 13 is inserted into the side of the access passage 14, and chemical solution is injected to form a buffer body 12. By solidifying in an unsaturated state, the energy acting from the outside can be attenuated.

[0036] Figure 2 is a schematic diagram showing a scenario where there are no buried pipes near the existing underground structure 21. An access passage 25 connecting the ground surface to the existing underground structure 21 is provided on the side of the existing underground structure 21. In this case, drilling can be performed from the ground surface and the injection pipe 24 can be installed.

[0037] Microbubble water is injected near the existing underground structure 21 to desaturate it and 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 silica grout containing microbubbles or a watertight wall 23 made of silica grout is constructed to prevent the advection and diffusion of the microbubble water.

[0038] This method allows for low saturation and reliable desaturation by separating the formation of the buffer 22 through desaturation from the construction of the impermeable wall 23.

[0039] Figure 3 is a schematic diagram showing a scenario where there are no buried pipes near the existing underground structure 31, assuming conditions of high blast pressure. An access passage 35 connecting the ground surface to the existing underground structure 31 is provided on the side of the existing underground structure 31. In this case, drilling can be performed from the ground surface and injection pipes 34 can be installed.

[0040] If a missile lands near an existing underground structure 31, or if a missile with a large amount of explosive is launched, desaturation by microbubbles alone may not be sufficient to attenuate the blast pressure. In such cases, by injecting suspension-type grout along the existing underground structure 31 and increasing the apparent wall thickness, it is possible to withstand the impact of the blast pressure. In Figure 3, a reinforcing body 32 made of suspension-type grout is formed along the outer circumference of the existing underground structure 31, and a buffer body 33 made of silica grout containing microbubbles is constructed on the outside of it.

[0041] Furthermore, the existing underground structures in this invention may be any structures located in the ground, such as tunnels, subway stations, underground shopping areas, or underground passages. In addition, the performance of structures originally designed as underground shelters can be improved by forming a buffer on their outer perimeter.

[0042] The injection materials used in the reinforcement method for existing underground structures of the present invention include microbubbles and silica grout containing microbubbles for constructing a buffer body, silica grout for constructing a watertight wall to prevent the advection and diffusion of bubbles, and suspension grout for improving impact resistance against blast pressure. It is also preferable to use solution-type injection materials or suspension-type injection materials that the applicant has already developed as permanent grout with expected long-term durability and whose sustained ground improvement effect has been demonstrated.

[0043] In the method for reinforcing existing underground structures according to the present invention, the range of the buffer due to desaturation and the injection range and strength of the suspension-type injection material for reinforcement are designed to withstand the blast pressure caused by the expected explosion energy of a ballistic missile.

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

[0045]

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[0049] Next, the bearing capacity of the underground structure against the calculated blast pressure is checked. While FEM analysis is an effective method for this check, a simpler method is also to examine the degree of damage based on wall thickness and blast pressure, as shown in Table 1, which is based on experimental results regarding blast pressure and reinforced concrete damage described in Non-Patent Literature 8.

[0050] [Table 1]

[0051] If, after checking the blast pressure and the bearing capacity of the underground structure, there is a risk of damage to the underground structure, a buffer will be constructed by desaturating the ground to reduce the blast pressure.

[0052] If the blast pressure acting on the underground structure remains high even after constructing a buffer by desaturating the ground, a suspension-type grout is injected into the ground adjacent to the underground structure to increase the apparent wall thickness of the structure.

[0053] Furthermore, when the ground is desaturated, it exhibits the characteristic of decreasing longitudinal elastic waves, as shown in Figure 3. The invention described in Patent Document 8 is an effective method for confirming the quality of improved ground using this property, and it can also be utilized in this patented technology.

[0054] [Example 1] This section presents an example of a study under the following conditions: The calculation assumes a missile weighing 1000 kg of TNT lands approximately 30 m 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 using Equation 1, is approximately 260 kPa, as shown in Figure 4. It is generally understood that concrete structures will suffer some degree of damage when 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 it to 80%, the blast pressure can be reduced to 50 kPa or less, as shown in Figure 4, and the soundness of the concrete can be maintained.

[0057] [Example 2] This section presents an example of a study under the following conditions: The calculation assumes a missile weighing 2000 kg of TNT lands approximately 30 m from an underground structure with a wall thickness of 100 mm. The target ground is sandy soil and is saturated.

[0058] When the blasting earth pressure is calculated from Equation 1, it becomes about 400 kPa as shown in Figure 4, and damage will surely occur to the concrete structure.

[0059] Inject microbubbles around the structure to reduce the saturation S r to 80%. As shown in Figure 4, the blasting earth pressure can be reduced to 100 kPa or less, but there is still a possibility of damage to the concrete.

[0060] In such a case, as shown in Figure 3, inject a suspension-type injection material around the underground structure to increase the apparent wall thickness and ensure the cross-sectional rigidity. Note that the minimum improvement thickness is preferably about 0.5 m to ensure the continuity of the improved body.

[0061] The required improvement thickness by the suspension-type injection material is such that the uniaxial compressive strength q u of the suspension-type injection material is about 1 to 10 MN / m 2 and the deformation coefficient E is about 0.1 to 2.0 GN / m 2 , which 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... Embedded objects (sewer pipes, gas pipes, etc.) 11... Existing underground structure 12... Improved body (buffer body) by silica grout containing microbubbles 13... Injection pipe 14... Access passage 21... Existing underground structure 22... Buffer body by microbubbles · 23... Waterproof wall by silica grout 24... Injection pipe 25... Access passage 31... Existing underground structure 32... Reinforcement body of existing underground structure by suspension-type injection material 33... Buffering material made of silica grout containing microbubbles 34...Injection tube 35…Access passage

Claims

1. A method for reinforcing an existing underground structure, characterized by constructing a buffer around the outer perimeter of the existing underground structure by performing ground improvement using a chemical grout injection method on the ground around the outer perimeter of the existing underground structure, thereby reducing the degree of soil saturation and making it unsaturated, and thereby attenuating energy acting from the outside.

2. A method for reinforcing an existing underground structure according to claim 1, characterized in that the injection material used in the chemical grout injection method is any of the following: microbubbles, silica grout, silica grout containing microbubbles, a combination of microbubbles and silica grout containing microbubbles, or a combination of microbubbles and silica grout.

3. A method for reinforcing an existing underground structure according to claim 2, characterized in that the injection material further includes a radiation shielding material mainly composed of clay as the injection material.

4. A method for reinforcing an existing underground structure according to claim 1, 2, or 3, characterized in that a suspension-type injection material is injected into the inside of the buffer body to form a reinforcing body before constructing the buffer body.

5. A method for reinforcing an existing underground structure according to claim 1, 2, or 3, characterized in that the existing underground structure is an existing underground shelter.

6. A method for reinforcing an existing underground structure according to claim 1, 2, or 3, characterized in that the range and strength of the buffer are designed to have strength and range that can withstand the explosive energy of an assumed ballistic missile.

7. A method for reinforcing an existing underground structure according to claim 6, characterized in that the range and strength of the buffer are calculated by converting the explosion energy into seismic energy.

8. A method for reinforcing an existing underground structure according to claim 6, characterized in that the range and strength of the buffer body are calculated by converting the explosion energy into blast pressure.

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