Ground improvement method and ground improvement system

Abstract

This invention provides a ground improvement method that can capture carbon dioxide from the atmosphere and fix it in the liquid component of the excavated sludge. [Solution] The ground improvement method includes a step of blowing air into the liquid component 51 in the discharged sludge 21 from a cement solidification method in which a cement-based solidification material 15 containing cement and water is mixed with the soil to be improved, and reacting the carbon dioxide in the air with the calcium in the liquid component 51 to produce calcium carbonate-containing water.

Description

[Technical Field]

[0001] The present invention relates to a ground improvement method and a ground improvement system. [Background technology]

[0002] Conventionally, the high-pressure jet agitation method, which involves injecting a solidifying agent into the ground from a rotary injection pipe to form an improved body, is known as a ground improvement method. However, the high-pressure jet agitation method generates sludge containing excess solidifying agent when creating the improved ground body. Conventionally, it has been known to effectively utilize the sludge discharged when creating the improved ground body.

[0003] Patent Document 1 discloses a ground improvement method using a high-pressure jet agitation method, which includes a measurement step for measuring the properties of excess solidified material that serve as an indicator of strength, and an excess solidified material strength estimation step for estimating the strength of the excess solidified material after solidification based on the measured properties of the excess solidified material. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2023-121640 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] On the other hand, in recent years, global warming caused by carbon dioxide released into the atmosphere has become a problem, and measures to reduce carbon dioxide in the atmosphere are being considered as a countermeasure against global warming.

[0006] This invention has been made in view of the problems of the prior art. The object of this invention is to provide a ground improvement method and a ground improvement system that can recover carbon dioxide from the atmosphere and fix it in the liquid component of the excavated sludge. [Means for solving the problem]

[0007] A ground improvement method according to a first aspect of the present invention includes a step of blowing air into the liquid component of the excavated sludge discharged in a cement solidification method in which a cement-based solidification material containing cement and water is mixed with the soil to be improved, and reacting the carbon dioxide in the air with the calcium in the liquid component to produce calcium carbonate-containing water.

[0008] A ground improvement system according to a second aspect of the present invention includes an aeration tank that blows air into the liquid component of the sludge discharged in a cement solidification method in which a cement-based solidification material containing cement and water is mixed with the soil to be improved, and reacts carbon dioxide in the air with calcium in the liquid component to produce calcium carbonate-containing water. [Effects of the Invention]

[0009] According to this disclosure, it is possible to provide a ground improvement method and a ground improvement system that can recover carbon dioxide from the atmosphere and fix it in the liquid component of the excavated sludge. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram showing a ground improvement system according to one embodiment. [Modes for carrying out the invention]

[0011] The following describes in detail, with reference to the drawings, the ground improvement system 1 and the ground improvement method using the ground improvement system 1 according to this embodiment. Note that the dimensional ratios in the drawings are exaggerated for illustrative purposes and may differ from the actual ratios.

[0012] The ground improvement system 1 according to this embodiment includes a ground improvement device 10, a first pump 20, a solid-liquid separation device 30, an aeration tank 50, a silo 60, a mixer 61, and a storage tank 62.

[0013] The ground improvement device 10 is a device for performing ground improvement. In this embodiment, the high-pressure jet agitation method will be described as an example of a ground improvement method performed using the ground improvement device 10.

[0014] The ground improvement device 10 includes a pipe rod 11 that can be penetrated into the ground 2, and a construction machine 12 that inserts or withdraws the pipe rod 11 to a predetermined depth. A stirring head 13 is provided at the lower part of the pipe rod 11. The stirring head 13 includes an injection nozzle 14, and the cement-based solidifying material 15 flowing inside the pipe rod 11 is injected from the injection nozzle 14.

[0015] In the high-pressure jet mixing method, first, a crawler-type construction machine may be used to inject high-pressure water from the tip of the pipe rod 11 while lowering the pipe rod 11 to drill the ground 2 to a predetermined depth and form a guide hole 3.

[0016] Next, the pipe rod 11 is inserted into the guide hole 3 to a predetermined depth, and the stirring head 13 is rotated while injecting the cement-based solidifying material 15 from the injection nozzle 14 into the ground 2 at high pressure. The cement-based solidifying material 15 is supplied to the injection nozzle 14 at high pressure from a water tank or a plant (not shown). The ground 2 is cut by the injection of the cement-based solidifying material 15, and the improved target soil, which is the cut ground 2, and the cement-based solidifying material 15 are stirred and mixed.

[0017] Next, while withdrawing the pipe rod 11 to a predetermined depth, the stirring head 13 is rotated and the cement-based solidifying material 15 is injected to cut the ground 2 with the cement-based solidifying material 15 and stir and mix the improved target soil and the cement-based solidifying material 15. Thereby, a columnar improved body is formed in the ground 2. In the high-pressure jet mixing method, the ground 2 can be improved by the improved body formed in this way.

[0018] On the other hand, in the high-pressure jet mixing method, a part of the improved target soil and the cement-based solidifying material 15 becomes slurry-like sludge 21 and flows upward through the horizontal gap of the pipe rod 11 in the guide hole 3. The sludge 21 is discharged from the guide hole 3 to a sludge pit 4 provided on the ground surface and stored in the sludge pit 4.

[0019] The high-pressure jet mixing method may be a single-pipe high-pressure jet mixing method, a double-pipe high-pressure jet mixing method, or a triple-pipe high-pressure jet mixing method. The single-pipe high-pressure jet mixing method is a method in which a cement-based solidifying material 15 is injected from a single-pipe pipe rod 11 to cut the ground 2 and form a modified body. The double-pipe high-pressure jet mixing method is a method in which a cement-based solidifying material 15 accompanied by air is injected from a double-pipe pipe rod 11 to cut the ground 2 and form a modified body. The triple-pipe high-pressure jet mixing method is a method in which a cement-based solidifying material 15 and high-pressure water accompanied by air are injected from a triple-pipe pipe rod 11 to cut the ground 2 and form a modified body.

[0020] The cement-based solidifying material 15 contains cement and water and is also called cement slurry or cement milk. The cement only needs to contain calcium and may include known cements such as Portland cement and blast furnace cement having calcium silicate as the main component. The cement-based solidifying material 15 may contain additives as necessary in addition to cement and water. Examples of the additives include a viscosity modifier for adjusting the viscosity of the cement-based solidifying material 15.

[0021] A first pump 20 is arranged in the sludge pit 4. The first pump 20 moves the sludge 21 discharged by the high-pressure jet mixing method and stored in the sludge pit 4 to the solid-liquid separation device 30 through the first pipe 22.

[0022] The solid-liquid separation device 30 separates the solid components 32, 39 and the liquid component 51 from the sludge 21. The solid components 32, 39 separated by the solid-liquid separation device 30 may be discarded. The liquid component 51 separated by the solid-liquid separation device 30 is sent to the aeration tank 50. The solid-liquid separation device 30 may include only one separation device or may include a plurality of separation devices. In the present embodiment, the solid-liquid separation device 30 includes a first solid-liquid separation device 31, a sludge tank 33, and a second solid-liquid separation device 37.

[0023] The first solid-liquid separator 31 separates large-diameter particles 32, which are solid components, from the sludge 21. The large-diameter particle-excluded sludge 34, which is the liquid component from which the large-diameter particles 32 have been removed in the first solid-liquid separator 31, is stored in the sludge tank 33. The first solid-liquid separator 31 may include, for example, a screen mesh, and the large-diameter particles 32 may be separated from the sludge 21 by the screen mesh. The large-diameter particles 32 may be, for example, particles with a diameter of 9.5 mm or more. The large-diameter particles 32 may include gravel, soil clumps, and coarse material.

[0024] A second pump 35 is located in the sludge tank 33. The second pump 35 sends the large-diameter particle-removed sludge 34 stored in the sludge tank 33 to the second solid-liquid separator 37 via the second piping 36.

[0025] The second solid-liquid separator 37 separates small-diameter particles 39, which are solid components, and liquid components 51 from the large-diameter particle-removed sludge 34 separated by the first solid-liquid separator 31. The small-diameter particles 39 separated by the second solid-liquid separator 37 are transported by a belt conveyor 40 and collected as separated soil 41, and then transported by a material transport vehicle such as a backhoe. The liquid components 51 are sent to the aeration tank 50 via the third pipe 38.

[0026] Small-diameter particles 39 are particles with a smaller diameter than large-diameter particles 32. Small-diameter particles 39 may include, for example, sand and aggregates. Sand refers to particles with a diameter of 1 / 16 mm or more and 2 mm or less. Small-diameter particles 39 may also be particles smaller than 9.5 mm. The second solid-liquid separator 37 includes a centrifugal separator, such as a decanter-type centrifugal separator, and the small-diameter particles 39 in the large-diameter particle-excluded sludge 34 may be classified and recovered by the centrifugal separator. If the large-diameter particle-excluded sludge 34 contains a large amount of silt, a coagulant may be added to the large-diameter particle-excluded sludge 34, and the aggregates generated by the addition of the coagulant may be separated by the second solid-liquid separator 37.

[0027] In this embodiment of the ground improvement system 1, the sludge 21 in the sludge pit 4 was separated using the first pump 20 and the solid-liquid separator 30, but the system is not limited to this configuration. For example, the sludge 21 may be moved to the solid-liquid separator 30 using a material transport vehicle such as a backhoe. Alternatively, only the liquid component 51 in the sludge 21 may be sent to the aeration tank 50.

[0028] The aeration tank 50 stores liquid components 51, which have a lower specific gravity than the sludge 21 after the solid components 32 and 39 have been removed from the sludge 21. An aeration device 52 is located at the bottom of the aeration tank 50 to supply air to the liquid components 51 inside the aeration tank 50. The aeration device 52 is connected to a compressor 53. Air from the atmosphere taken in by the compressor 53 is supplied to the aeration device 52 through an air supply pipe 54. Then, the air is supplied from the aeration device 52 to the liquid components 51 inside the aeration tank 50.

[0029] In the aeration tank 50, carbon dioxide from the air is fixed in the liquid component 51. The discharged sludge 21 contains a cement-based solidifying agent 15 used in the high-pressure jet agitation method. This cement-based solidifying agent 15 contains a large amount of cement. Cement contains a large amount of calcium, and calcium ions are dissolved in the liquid component 51 in the discharged sludge 21. Therefore, air is blown into the liquid component 51 in the discharged sludge 21, causing the carbon dioxide from the air to react with the calcium in the liquid component 51 to produce calcium carbonate-containing water. This allows carbon dioxide from the atmosphere to be absorbed and fixed in the liquid component 51.

[0030] Specifically, when carbon dioxide diffuses into liquid component 51 in the form of fine particles from the air, according to Henry's Law, the carbon dioxide in the air dissolves in the water in liquid component 51 in proportion to the water pressure. The carbon dioxide (CO2) dissolved in water becomes carbonic acid (H2CO3), as shown in the reaction equation (1) below.

[0031] CO2 + H2O → H2CO3 (1)

[0032] Carbonic acid (H2CO3) dissociates into hydrogen ions (H

[0036] ), producing bicarbonate ions (HCO3 - ) and carbonate ions (CO3 2- ), as shown in the following reaction equations (2) and (3).

[0033] H2CO3 → H + + HCO3 - (2) HCO3 - → H + + CO3 2- (3)

[0034] Carbonate ions (CO3 2- ) combine with calcium ions (Ca 2+ ) derived from cement to form calcium carbonate, as shown in the following reaction equation (4).

[0035] CO3 2- + Ca 2+ → CaCO3 (4)

[0036] Calcium carbonate has low solubility in water and is a stable solid. Since carbon dioxide in the air can be recovered as calcium carbonate and fixed, the carbon dioxide in the air can be reduced. In addition, since the calcium carbonate-containing water contains fine particles of calcium carbonate, using the calcium carbonate-containing water as a raw material for the cement-based solidifying material 15 may improve the strength of the improved body formed by the cement-based solidifying material 15. In such a case, the amount of the cement-based solidifying material 15 used can be reduced.

[0037] The silo 60 stores powdered cement. The mixer 61 mixes the cement stored in the silo 60 and the calcium carbonate-containing water to produce the cement-based solidifying material 15. The cement only needs to contain calcium as described above, and may be a known cement such as Portland cement and blast furnace cement mainly composed of calcium silicate, for example.

[0038] Mixer 61 is connected to aeration tank 50 via fourth piping 56. A third pump 55 is located in aeration tank 50, and calcium carbonate-containing water generated in aeration tank 50 by the third pump 55 is supplied to mixer 61 via fourth piping 56. A flow control valve 57 is provided in fourth piping 56. The flow control valve 57 can adjust the flow rate of calcium carbonate-containing water supplied from aeration tank 50 to mixer 61. In addition to cement and calcium carbonate-containing water, water such as tap water or industrial water, and additives may be added to mixer 61. Storage tank 62 includes an agitator (not shown) and stores the cement-based solidifying material 15 generated in mixer 61 while stirring it with the agitator. The cement-based solidifying material 15 stored in storage tank 62 is supplied to a water tank or plant (not shown) or directly to an injection nozzle 14.

[0039] The ground improvement device 10 uses the cement-based solidification material 15 containing calcium carbonate water, which is produced as described above, in the cement solidification method described above. Through this process, the cement-based solidification material 15 can be recycled, and carbon dioxide can be fixed into the ground 2.

[0040] The additive may include a viscosity modifier to adjust the viscosity of the cement-based solidifying agent 15. Since calcium carbonate is present in the form of fine particles in calcium carbonate-containing water, the viscosity of the cement-based solidifying agent 15 may increase. Therefore, the viscosity of the cement-based solidifying agent 15 may be adjusted with a viscosity modifier before use.

[0041] Furthermore, the sludge 21 contains the cement mentioned above and tends to have a high pH. On the other hand, the pH of the liquid component 51 is due to the H produced by reaction equations (2) and (3). +This can be done to lower the pH. As a result, the pH of the sludge 21 can be lowered to neutral. This allows calcium carbonate-containing water with a pH lower than that of the sludge 21 to be used as a raw material for the cement-based solidifying agent 15. Therefore, it is possible to prevent the cement from hardening too quickly due to a high pH, ​​which would increase the viscosity of the cement-based solidifying agent 15, reduce its fluidity, and hinder the flow of the cement-based solidifying agent 15.

[0042] Furthermore, the above embodiment described a high-pressure jet agitation method. However, the ground improvement method according to this embodiment is not limited to the high-pressure jet agitation method and can be applied to a cement solidification method that mixes a cement-based solidifying material 15 with the soil to be improved in the ground 2. The cement solidification method is preferably, for example, a mid-layer mixing method or a deep-layer mixing method. These methods are highly effective in reducing the amount of waste sludge 21 to be disposed of, as a large amount of waste sludge 21 is generated during the construction process. In addition, the cement solidification method is not limited to the high-pressure jet agitation method and may be a mechanical agitation method, a mechanical / jet combined agitation method, or a soil-cement diaphragm wall method. Among these, the high-pressure jet agitation method or the mechanical / jet combined agitation method used in the deep-layer mixing method is preferred as the cement solidification method because a particularly large amount of waste sludge 21 is generated during the construction process.

[0043] As explained above, the ground improvement method includes a step of blowing air into the liquid component 51 in the discharged sludge 21 of the cement solidification method, which involves mixing a cement-based solidification material 15 containing cement and water with the soil to be improved, and reacting the carbon dioxide in the air with the calcium in the liquid component 51 to produce calcium carbonate-containing water.

[0044] Furthermore, the ground improvement system 1 includes an aeration tank 50 that blows air into the liquid component 51 in the discharged sludge 21 produced by the cement solidification method, which involves mixing a cement-based solidification material 15 containing cement and water with the soil to be improved, and reacts carbon dioxide in the air with calcium in the liquid component 51 to produce calcium carbonate-containing water.

[0045] According to the ground improvement method and ground improvement system 1 of this embodiment, carbon dioxide from the atmosphere can be recovered and fixed in the liquid component 51 of the excavated sludge 21.

[0046] The ground improvement method may include a step of mixing calcium carbonate-containing water and cement to produce a cement-based solidifying agent 15.

[0047] Traditionally, the sludge 21 discharged from cement solidification construction methods was disposed of as industrial waste. However, the disposal costs of sludge 21 are high, and it is desirable to utilize it effectively. Furthermore, a relatively large site is required to install a sludge pit 4 and associated equipment for disposing of the sludge 21. In sites where such a large site cannot be secured, the sludge 21 is sometimes collected using vacuum trucks. However, if there are time constraints on collection by vacuum trucks, the number of construction projects that can be completed may be reduced.

[0048] On the other hand, according to the ground improvement method of this embodiment, carbon dioxide can be fixed within the liquid component 51 recovered from the excavated sludge 21 by blowing air into the liquid component 51. Furthermore, the liquid component 51 with fixed carbon dioxide is used as a raw material for the cement-based solidification material 15. Therefore, according to the ground improvement method and ground improvement system 1 of this embodiment, the amount of excavated sludge 21 to be disposed of can be reduced by recycling the excavated sludge 21, and carbon dioxide from the atmosphere can be recovered and fixed in the improved body. Thus, the cost required for disposal of excavated sludge 21 can be reduced, and carbon neutrality can be contributed to.

[0049] The cement solidification method may also be a high-pressure jet agitation method. The high-pressure jet agitation method is particularly effective in reducing the amount of waste sludge 21 to be disposed of, as a large amount of waste sludge 21 is generated during the construction process.

[0050] The ground improvement method may include a step of separating liquid components 51 from the excavated sludge 21. This step allows for easy removal of solid components such as large-diameter particles 32 or small-diameter particles 39 from the excavated sludge 21. Furthermore, calcium carbonate-containing water can be efficiently produced from the separated liquid components 51.

[0051] The ground improvement method may include a step of using a cement-based solidifying agent 15 containing calcium carbonate water in a cement solidification method. Through such a step, the cement-based solidifying agent 15 can be recycled and carbon dioxide can be fixed into the ground 2.

[0052] Although this embodiment has been described above, this embodiment is not limited to these, and various modifications are possible within the scope of the gist of this embodiment. [Explanation of Symbols]

[0053] 1. Ground Improvement System 10 Ground improvement equipment 15. Cement-based solidifying agent 21 Sludge removal 50 Aeration tanks 51 Liquid components 61 Mixer

Claims

1. A ground improvement method comprising the step of blowing air into the liquid component of the excavated sludge discharged in a cement solidification method in which a cement-based solidification material containing cement and water is mixed with the soil to be improved, and reacting the carbon dioxide in the air with the calcium in the liquid component to produce calcium carbonate-containing water.

2. The ground improvement method according to claim 1, further comprising the step of mixing the calcium carbonate-containing water with cement to produce a cement-based solidification material.

3. The ground improvement method according to claim 1 or 2, wherein the cement solidification method is a high-pressure injection mixing method.

4. A ground improvement method according to claim 1 or 2, comprising the step of separating the liquid component from the excavated sludge.

5. The ground improvement method according to claim 1 or 2, further comprising the step of using the cement-based solidification material containing the calcium carbonate-containing water in the cement solidification method.

6. A ground improvement system comprising an aeration tank that blows air into the liquid component of the discharged sludge from a cement solidification method, in which a cement-based solidification material containing cement and water is mixed with the soil to be improved, and reacts the carbon dioxide in the air with the calcium in the liquid component to produce calcium carbonate-containing water.

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