Ground compaction method

Abstract

To provide a ground compaction method which can effectively compact sandy soil in a saturated ground below the underground water level.SOLUTION: A ground compaction method includes an injection step of injecting a promoter (M) for promoting increase in density of a ground (1) formed by aggregating soil particles (D) onto the ground (1), and a loading step of applying a load to the ground (1), wherein the injection step and the loading step form a compaction region (1A) loaded by penetrating the promoter (M) in the ground (1).SELECTED DRAWING: Figure 1A

Description

[Technical Field]

[0001] The present invention relates to a method for compacting ground, particularly to a method for compacting sandy soil in a saturated state below the groundwater level. [Background technology]

[0002] The following Patent Document 1 discloses a method for preventing liquefaction of sandy ground. The liquefaction prevention method in Patent Document 1 involves inserting a pipe into the ground and injecting air into the pipe using an air injection device, injecting tiny air bubbles into the ground and forming an unsaturated layer in the ground, thereby preventing liquefaction. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2-125013 Summary of the Invention [Problem to be solved by the invention]

[0004] However, with the liquefaction prevention method described in Patent Document 1, it is difficult to inject uniform air bubbles into the ground, and in order to fully desaturate the ground, advanced injection techniques for permeation injection and a large amount of construction costs are required.On the other hand, a compaction method is also known as a liquefaction prevention measure, in which sand is compressed and sand piles are created to strengthen the surrounding ground.

[0005] The inventors conducted extensive research based on these methods and invented a method that can compact the ground more effectively.

[0006] An object of the present invention is to provide a ground compaction method that can effectively compact the ground. [Means for solving the problem]

[0007] The ground compaction method of the present invention comprises an injection step of injecting an accelerator into the ground, which accelerator promotes an increase in the density of the ground formed by the aggregation of soil particles, and a loading step of loading the ground. Through the injection step and the loading step, the accelerator penetrates and forms a loaded compacted area in the ground.

[0008] According to the above-mentioned ground compaction method, a compacted area is formed through the injection process and the loading process. For ground formed by agglomerated soil particles, the accelerator facilitates the rearrangement of the soil particles, promoting an increase in the density of the ground, thereby enabling the ground to be effectively compacted.

[0009] In the ground compaction method of the present invention, the injection process is a process of injecting the accelerator onto the construction surface where compaction is to be carried out on the ground, and the loading process can also be a process of applying a load to the construction surface.

[0010] According to the above-described ground compaction method, a spraying step and a loading step are carried out on the construction surface, so that a compacted area can be effectively formed.

[0011] In the ground compaction method of the present invention, the injection step and the loading step may be considered as a set of steps, and the set of steps may be carried out multiple times on the same construction surface.

[0012] According to the above-mentioned ground compaction method, the injection process and the loading process are treated as a set of processes, and by performing the set of processes multiple times on the same construction surface, the accelerator penetrates sufficiently into the ground and a sufficiently loaded compacted area is formed.

[0013] In the ground compaction method of the present invention, the loading process is a process of repeatedly loading and unloading the ground, and the injection process may include an intermediate injection process of injecting the accelerator into the ground in an unloaded state.

[0014] According to the above-mentioned ground compaction method, the accelerator is injected while the ground is unloaded as an intermediate injection step, and the accelerator penetrates smoothly into the ground by utilizing the reduced pressure that occurs during unloading.

[0015] The ground compaction method of the present invention can also be configured so that the injection step and the loading step form the compacted area in which the accelerator has permeated substantially the entire loaded area of ​​the ground.

[0016] According to the above-mentioned ground compaction method, a compacted area is formed in which the accelerator has permeated almost the entire loaded area, which makes it easier to increase the density of the entire compacted area of ​​the ground, thereby enabling effective compaction of the ground.

[0017] In the ground compaction method of the present invention, the accelerator may be an FB-containing liquid containing fine bubbles.

[0018] According to the above-mentioned ground compaction method, the fine bubbles have a friction-reducing effect of reducing friction between soil particles, and the negative charge of the fine bubbles causes them to adsorb to the positively charged minerals between the soil particles, allowing the accelerator to penetrate into the tiny gaps between the soil particles. This is expected to have a rearrangement-promoting effect of promoting the rearrangement of soil particles, thereby facilitating an increase in the density of the ground. [Effects of the Invention]

[0019] The ground compaction method of the present invention is a ground compaction method that can effectively compact the ground. [Brief explanation of the drawings]

[0020] [Figure 1A] FIG. 1 is a diagram showing a ground compaction method according to one embodiment of the present invention, in which (a) to (c) are diagrams showing the procedure from the pre-loading injection step to the first set of steps. [Figure 1B] 1B is a diagram showing a ground compaction method according to the embodiment, in which (d) and (e) are diagrams showing the procedure of a second set of steps carried out after the steps of FIG. 1A. [Figure 1C]1B is a diagram showing a ground compaction method according to the embodiment, in which (f) and (g) are diagrams showing the procedures of a loading step and a post-loading injection step carried out after the step of FIG. 1B. [Figure 2] (a) is a schematic diagram showing the gaps between soil particles in the ground before compaction in a saturated state, and (b) is a schematic diagram showing the gaps between soil particles after compaction in which the soil particles have been rearranged by carrying out the ground compaction method of the same embodiment. [Figure 3] 1 is a graph showing the relationship between repeated loading (vibration) time and relative density for an example of the present invention and a comparative example. [Figure 4] 1 is a graph showing the relationship between the number of repeated loadings and the repeated stress amplitude ratio for an example of the present invention and a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0021] A ground compaction method according to an embodiment of the present invention will be described below with reference to Fig. 1 (collectively referring to Figs. 1A, 1B, and 1C) to Fig. 4. The embodiment of the present invention is a ground compaction method useful for compacting ground 1, particularly for compacting liquefiable ground such as sandy soil (fine sandy ground) in saturated ground 1 below the groundwater level. Compaction is a construction method that aims to increase strength and improve water-stopping properties by rearranging soil particles in the case of sandy soil due to a load, or by consolidating clayey soil through drainage.

[0022] As shown in Fig. 1, the ground compaction method comprises an injection process and a loading process. The injection process is a process in which a fine bubble-containing liquid M (hereinafter simply referred to as FB-containing liquid) is injected into the ground 1 using an injection device S as an accelerator that promotes an increase in the density of the ground 1 formed by the collection of soil particles. The loading process is a process in which a horizontal load is applied to the ground 1 using a loading device K. In this way, the injection process and the loading process allow the FB-containing liquid M to penetrate and form a loaded compacted area 1A in the ground 1.

[0023] The FB-containing liquid M of this embodiment is an example of an accelerator and is water or other liquid containing bubbles (fine bubbles) with a diameter smaller than 100 μm. Examples of the FB-containing liquid M include microbubble-containing liquid M containing microbubbles with a diameter smaller than 100 μm but 1 μm or larger, and ultrafine bubble-containing liquid M containing ultrafine bubbles with a diameter smaller than 1 μm. The microbubble-containing liquid M is produced by a pressurized dissolution method. Other production methods include a gas-liquid two-phase shear method and a micropore method, but the pressurized dissolution method is preferred. This is because the reduced pressure (confining pressure in the ground minus the production pressure) when injected into the ground can be expected to result in a supersaturation effect of the microbubbles. Other methods for producing the ultrafine bubble-containing liquid M include an ultrasonic cavitation method and a high-speed swirling flow method.

[0024] Next, the ground compaction method will be described in detail. For convenience, the loading process will be described first. The loading process is a process of applying a load to a construction surface 2 of the ground 1 where compaction is to be performed using a loading device K (FIGS. 1A(b), 1B(d), and 1C(f)). In this embodiment, the above-mentioned load refers to applying a load to the construction surface 2 by using the loading device K to load the construction surface 2. The loading process refers to a process of pressing the construction surface 2 with the loading surface of the loading device K to apply a load, and then removing the loading surface of the loading device K from the construction surface 2 to unload it. In this embodiment, loading refers to pressing the loading surface of the loading device K against the construction surface 2 to apply a horizontal load to the ground 1 near the construction surface 2, and unloading refers to removing the loading surface of the loading device K from the construction surface 2 to remove the horizontal load on the ground 1 due to loading. This loading process is a process in which loading and unloading are repeated on the construction surface 2, and loading and unloading are repeated multiple times on the same part of the ground 1 (construction surface 2).

[0025] The injection process is a process of injecting the FB-containing liquid M onto the construction surface 2 where compaction is performed on the ground 1 (FIGS. 1A(a)(c), 1B(e), 1C(g)). In this embodiment, the injection process is performed by using an injection device S to spray the FB-containing liquid M in a mist onto the construction surface 2, and more specifically, the FB-containing liquid M is sprayed onto the construction surface 2 where the loading process is performed. This injection process includes a pre-loading injection process (FIG. 1A(a)), an intermediate injection process (FIGS. 1A(c), 1B(e)), and a post-loading injection process (FIG. 1C(g)).

[0026] The pre-loading injection process is a process of injecting the FB-containing liquid M using an injection device S before loading the construction surface 2 in the loading process, as shown in FIG. 1A(a), and is the first process performed in the ground compaction method. In this embodiment, the construction surface 2 in the subsequent loading process is set so as to include the area where the FB-containing liquid M was injected in the pre-loading injection process. Note that in this embodiment shown in FIG. 1, the construction surface 2 is described as a surface along the vertical direction of the ground 1, but the process of forming this construction surface 2 on the ground 1 is a separate process.

[0027] The mid-course injection step is a step of injecting the FB-containing liquid M into the ground 1 during the loading step, and is a step of injecting the FB-containing liquid M onto the construction surface 2 by the injection device S when the construction surface 2 is loaded in the loading step as shown in Fig. 1A(b) showing this embodiment and then unloaded as shown in Fig. 1A(c). In this mid-course injection step, the FB-containing liquid M is injected onto the entire or partial area of ​​the construction surface 2 that is loaded in the loading step.

[0028] Here, the loading step and the injection step are called a set of steps. Specifically, the set of steps includes loading of the construction surface 2 in the loading step, the subsequent unloading, and an injection step during the injection step (see Fig. 1A(b)(c)). In this embodiment, as shown in Fig. 1A(b)(c) and Fig. 1B(d)(e), the set of steps is performed multiple times on the same construction surface 2, and in this embodiment, it is performed twice.

[0029] The post-loading injection process is a process of injecting the FB-containing liquid M into the ground 1 after the loading process, and is a process of finally injecting the FB-containing liquid M onto the same construction surface 2. That is, after one set of processes is completed multiple times and the construction surface 2 is loaded as shown in Fig. 1C(f), the post-loading injection process is carried out (see Fig. 1C(g)).

[0030] As shown in FIG. 1A(a), the ground compaction method of this embodiment includes a pre-loading injection process. In this case, the construction surface 2 is not loaded by the loading device K, so there is no pressure bulb in the pre-loading injection process. However, in FIG. 1A(b), the construction surface 2 is loaded by the loading device K, and a compaction region 1A is created in the ground 1 by the pressure bulb, where the stress due to the loading acts, resulting in a bulb-shaped distribution of the stress. In FIG. 1A(c), the construction surface 2 is unloaded and the mid-stage injection process is performed. At this time, as the load state switches to the unloading state, the loaded region in the ground 1 enters a depressurized state due to the release of stress, and the FB-containing liquid M is injected into this depressurized region (construction surface 2) in the mid-stage injection process. Therefore, the FB-containing liquid M injected in the mid-stage injection process smoothly penetrates from the construction surface 2 into the ground 1 by utilizing the depressurization caused by the unloading. The process including the loading process (loading and unloading) and the injection process (intermediate injection process) in FIGS. 1A(b) and 1A(c) constitutes one set of processes.

[0031] Furthermore, as shown in Figure 1B(d), when the same surface of the construction surface 2 is loaded again using the loading device K, the area where the stress acts spreads further into the ground 1 (becoming a pseudo-loading surface in the ground) through the compacted area 1A created by the pressure bulb created by the preceding loading process in Figure 1A(b), and the pressure bulb expands further into the ground 1. Since the FB-containing liquid M injected in the intermediate injection process of the preceding injection process in Figure 1A(c) has permeated this pressure bulb, the penetration (supply) of the preceding FB-containing liquid M further into the ground 1 due to the penetration of the subsequent FB-containing liquid M, and the pseudo-loading effect of the preceding compacted area 1A, causes the pressure bulb to expand and the new compacted area 1A to expand over a wide area until the effects of the loading are felt.

[0032] Thereafter, as shown in FIG. 1B(e), the load is removed again and the intermediate injection process is performed. At this time, too, the reduced pressure caused by the unloading is utilized to smoothly infiltrate the FB-containing liquid M into the construction surface 2. The process including the loading process (loading, unloading) and the injection process (intermediate injection process) in FIGS. 1B(d)(e) up to this point is also a set of processes, and in this embodiment, one set of processes is performed twice. Furthermore, as shown in FIG. 1C(f), by loading the same construction surface 2 again, the range in which the stress caused by the loading acts expands further into the ground 1, the size of the pressure bulb decreases, and the compacted area 1A grows deeper into the ground 1 to the extent that the influence of the loading reaches, and the FB-containing liquid M also infiltrates deeper into the ground 1.

[0033] FIG. 1C(g) shows the post-load injection process. A set of steps is repeated multiple times as a previous step. After the pressure bulb expands, the FB-containing liquid M is finally injected onto the same construction surface 2. Here, too, the reduced pressure caused by unloading is utilized to smoothly infiltrate the FB-containing liquid M into the construction surface 2. By performing the above steps, the FB-containing liquid M as an accelerator penetrates and a loaded compacted area 1A is formed on the far side of the construction surface 2 of the ground 1. Furthermore, by setting the injection conditions for the FB-containing liquid M in the injection process taking into account the range of the pressure bulb on the far side, which is the loaded area, it is possible to form a compacted area 1A in which the FB-containing liquid M has penetrated into almost the entire loaded area of ​​the ground 1. Specifically, the injection conditions, such as the injection amount and injection pressure of the FB-containing liquid M in the injection process, are set so that the FB-containing liquid M penetrates, for example, half or more of the area where stress due to loading acts in the loading process. In this embodiment, the FB-containing liquid M penetrates the entire area. In this embodiment, an example of performing each process on one construction surface 2 has been described, but for example, by performing each of the above processes on the entire vertical surface along the top and bottom of the ground 1, it is possible to form a compacted ground in which the compaction area 1A is continuous from top to bottom.

[0034] In the ground compaction method of this embodiment as described above, an injection process is carried out in which FB-containing liquid M is injected into the ground 1 as an accelerator to promote an increase in the density of the ground 1, and a loading process is carried out in which a load is applied to the ground 1.The FB-containing liquid M penetrates the ground 1 and forms a loaded compacted area 1A in the ground 1.Since the density of the ground 1 is increased by the FB-containing liquid M and the loading, the ground 1 can be effectively compacted, compared to the ground 1 which is formed by a collection of soil particles.

[0035] Here, the effect of the FB-containing liquid M in promoting an increase in the density of the ground 1 will be described in detail. The accelerator of the present invention promotes an increase in the density of the ground 1 by reducing friction between soil particles in the ground 1 and by adsorbing minerals in the gaps between the soil particles due to its negative charge. Specifically, the FB-containing liquid M used as the accelerator in this embodiment is a liquid containing fine bubbles. These fine bubbles penetrate between the soil particles in the ground 1, thereby reducing friction between the soil particles in contact with each other (friction-reducing effect), thereby increasing the rearrangement of the soil particles. Furthermore, because the fine bubbles in the FB-containing liquid M are negatively charged, they have the effect of adsorbing to positively charged soil particles of minerals such as clay minerals and oils (adsorption effect). This allows the FB-containing liquid M to easily penetrate into the fine gaps between the soil particles, thereby increasing the density of the ground 1. Typically, ground 1 is a mixture of densely packed and sparsely packed areas of soil particles. However, due to the adsorption properties of the negative charge of fine bubbles, the FB-containing liquid M penetrates into the fine gaps between the soil particles not only in the coarse areas but also in the dense areas (adsorption effect). By performing the ground compaction method of this embodiment, which includes a spraying process and a loading process using the FB-containing liquid M having such friction-reducing and adsorption effects, on a sandy soil ground 1 that is saturated below the groundwater level, for example, the gaps between the soil particles D before construction as shown in FIG. 2(a) change from a coarse state, as shown in FIG. 2(b), to a densely packed state, as shown in FIG. 2(b), with the FB-containing liquid M penetrating into the fine gaps between the soil particles D after construction, thereby increasing the density of the ground 1. In other words, by performing the spraying process and loading process using an accelerator, the friction-reducing and adsorption effects of the accelerator can be expected to promote the rearrangement of the soil particles in the ground 1, and the density of the ground 1 can be expected to increase.

[0036] Furthermore, in the ground compaction method of this embodiment, the injection process is a process of injecting the FB-containing liquid M onto the construction surface 2 of the ground 1, and the loading process is a process of loading onto the construction surface 2, so that by carrying out the process on the surface of the ground 1, a compaction area 1A can be effectively formed.

[0037] Furthermore, in the ground compaction method of this embodiment, by performing a set of processes including an injection process and a loading process multiple times on the same construction surface 2, the FB-containing liquid M can be penetrated deep into the ground 1 to form a loaded compacted area 1A.

[0038] In addition, in the ground compaction method of this embodiment, the injection process and loading process are repeated to form the compacted area 1A, and the penetration of the FB-containing liquid M continues through the subsequent injection process and loading process, thereby enabling effective compaction even outside the compacted area 1A (uncompacted area), effectively forming a wide-area compacted area 1A that is affected by the loading.

[0039] Furthermore, in the ground compaction method of this embodiment, as an intermediate injection step in the injection process, the FB-containing liquid M is injected onto the construction surface 2 of the ground 1 in an unloaded state, so that the FB-containing liquid M can be smoothly infiltrated into the ground by utilizing the reduced pressure that occurs during unloading.

[0040] Furthermore, in the ground compaction method of this embodiment, by setting the conditions of the injection process in consideration of the size of the pressure bulb caused by loading in the loading process, it is possible to form a compacted area 1A in which the FB-containing liquid M has permeated almost the entire loaded area of ​​the ground 1. Furthermore, since the compacted area 1A in which the FB-containing liquid M has permeated almost the entire loaded area is formed, the density of the entire compacted area 1A of the ground 1 is likely to increase, allowing for effective compaction.

[0041] Next, a compaction experiment using the ground compaction method of the present invention will be described. Test specimens of ground 1, in which the soil particles were silica sand and the relative density was 60% using the air-drop method, were prepared. One test specimen was saturated with deaerated water (B value 95% or higher) and repeatedly loaded and unloaded with 60 Hz vibration (cyclic loading) to prepare a comparative test specimen. The other test specimen was saturated with deaerated water, and then microbubble-containing water was injected at an injection rate of 10 ml / min for 60 minutes, followed by repeated loading and unloading with 60 Hz vibration (cyclic loading) to prepare an example test specimen. The microbubble-containing water was generated using a pressurized dissolution method, with a generation pressure of 400 kPa and a dissolved oxygen content of 10 to 12 mg / L. The results of the comparative experiment between these examples and comparative examples are explained using the graph in Figure 3, which shows the change in relative density versus cyclic loading (vibration) time. In Figure 3, the horizontal axis is the "repeated loading (vibration) time" (unit: sec), which is the time during which compaction was carried out, and the vertical axis is the "relative density" (unit: %), which indicates the degree of compaction of the test specimen. Also in Figure 3, the dashed line is the test specimen of the comparative example, which was compacted without using microbubble-containing water, and the solid line is the test specimen of the example.

[0042] As is clear from Figure 3, the relative density of the specimen of the example is improved compared to the specimen of the comparative example. In other words, by carrying out the ground compaction method using microbubble-containing water as an accelerator of the present invention on saturated ground 1 below the groundwater level, the degree of compaction of the ground 1 (increase in density) is improved.

[0043] Furthermore, to compare the liquefaction strength between the above-mentioned Example and Comparative Example, a cyclic undrained triaxial test (liquefaction test) was conducted, and the results are shown in Figure 4. Figure 4 shows the liquefaction strength curve when the double amplitude axial strain is 5%, with the horizontal axis representing the "number of repeated loadings" (unit: Nc), which is the number of times loading and unloading were repeated, and the vertical axis representing the "cyclic stress amplitude ratio" (unit: σ d / 2σ'0). In FIG. 4, the dashed line indicates the specimen of the comparative example, and the solid line indicates the specimen of the example.

[0044] As is clear from Figure 4, the specimens of the Example have an improved cyclic stress amplitude ratio compared to the specimens of the Comparative Example. Therefore, it can be seen that the liquefaction strength of ground subjected to the ground compaction method of the present invention is also improved. Note that liquefaction strength refers to the strength of saturated soil subjected to cyclic stresses such as those caused by earthquakes under undrained conditions.

[0045] Thus, according to the ground compaction method of this embodiment, the friction-reducing effect of the FB-containing liquid M as an accelerator and the particle rearrangement promoting effect of the soil particles due to the adsorption effect of the negative chargeability can rearrange the soil particles so that they are densely packed together, increasing the density of the ground 1 and effectively compacting the ground 1. In addition, a synergistic effect can be expected in that the presence of the FB-containing liquid M in the ground 1 after construction also improves the liquefaction strength (liquefaction resistance).

[0046] The present invention can be modified in various ways without departing from the spirit and scope of the invention. The specific configurations of the various parts are not limited to the above-described embodiments.

[0047] The injection process of the ground compaction method in the above embodiment includes pre-load injection, mid-load injection, and post-load injection. However, it is possible to perform any one of pre-load injection, mid-load injection, and post-load injection, or any two of them. Furthermore, mid-load injection can be a process that can be performed when the construction surface 2 is loaded, when it is unloaded, or both when it is loaded and unloaded. Furthermore, the injection process can be performed continuously from before loading the construction surface 2 to after loading.

[0048] In the ground compaction method of the above embodiment, one set of steps is repeated twice, but it may be repeated once, or three or more times.

[0049] In addition, in this embodiment, a series of steps from the pre-loading injection step to the post-loading injection step has been described, but in the ground compaction method of the present invention, for example, the injection step can be a pre-loading injection step, and only the pre-loading injection step and the loading step can be carried out, or only the set of steps can be carried out. Also, the injection step can be such that the accelerator is injected during loading in the loading step.

[0050] In the above embodiment, the FB-containing liquid M was cited as an example of an accelerator that has both a friction-reducing effect and an adsorption effect to minerals and the like due to its negative chargeability. However, in addition to the FB-containing liquid M, lubricating liquids serving as friction reducers, such as soapy liquids as lubricants or silicone oils as fluidizing agents, can also be expected to promote an increase in the density of the ground 1 due to their friction-reducing effect. In other words, as long as they have at least the friction-reducing effect of both the friction-reducing effect and the adsorption effect due to their negative chargeability, they can be used as an accelerator to promote the rearrangement of soil particles in the ground 1 and promote an increase in density. However, FB-containing water is particularly suitable because it can be expected to have both a friction-reducing effect and an adsorption effect, and by remaining in the compaction area 1A after construction, it can be expected to improve liquefaction strength. Furthermore, it is environmentally friendly and inexpensive (no material costs are required).

[0051] The ground compaction method of the above embodiment is useful as a liquefaction countermeasure method, but it is also useful as a soil cement method in which local soil and slurry-based solidification material are mixed and stirred, or as a ground improvement method using a deep mixing treatment method, as it is expected that the mixing performance will be improved by improving the consistency using accelerators such as FB-containing water. [Explanation of symbols]

[0052] 1: Ground, 1A: Compaction area, 2: Construction surface, D: Soil particles, K: Loading device, M: FB-containing liquid, S: Injection device

Claims

1. The method includes an injection step of injecting an accelerator into the ground, which accelerator promotes an increase in the density of the ground formed by the collection of soil particles, and a loading step of applying a load to the ground, A ground compaction method, characterized in that the injection step and the loading step form a compacted area in the ground where the accelerator has penetrated and loaded.

2. The injection step is a step of injecting the accelerator onto a construction surface on the ground where compaction is to be performed, The ground compaction method according to claim 1 , wherein the loading step is a step of applying a load to the construction surface.

3. 3. The method of compacting ground according to claim 2, wherein the injection step and the loading step are considered as a set of steps, and the set of steps is carried out a plurality of times on the same construction surface.

4. The loading step is a step of repeatedly loading and unloading the ground, 4. The method for compacting ground according to claim 1, wherein the injection step includes an intermediate injection step of injecting the accelerator into the ground in an unloaded state.

5. 2. The method for compacting ground according to claim 1, wherein the compacted area in which the accelerator has permeated substantially the entire loaded area of ​​the ground is formed by the injection step and the loading step.

6. The ground compaction method according to claim 1, wherein the accelerator is an FB-containing liquid containing fine bubbles.

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