Ground stabilization method and pile driving method

Abstract

This invention provides a ground stabilization method that suppresses hexavalent chromium leaching, keeps the strength of the hardened soil cement relatively low, and reduces the amount of cement used. [Solution] The method employs a ground stabilization technique that includes the step of injecting a ground stabilization material into an excavated hole formed in the ground, and mixing the ground stabilization material with in-situ soil to form soil cement, wherein the ground stabilization material contains cement, blast furnace slag fine powder, water, and admixtures, and the cement is ordinary Portland cement or the like, and satisfies formulas (i) to (iii). 30≦C / (C+GGBFS)×100≦70 …(i) 150≦W / (C+GGBFS)×100≦250…(ii) 0≦SP / (C+GGBFS)×100≦5 …(iii) In equations (i) to (iii), C is the mass of cement (kg), GGBFS is the mass of blast furnace slag powder (kg), W is the mass of water (kg), and SP is the mass of the admixture (kg).

Description

[Technical Field]

[0001] The present invention relates to a ground stabilization method and a pile driving method. [Background technology]

[0002] The increasing density of buildings due to population concentration in urban areas, and the weight of disaster prevention facilities themselves due to the enhancement of disaster prevention facilities as part of national resilience measures, are leading to a growing demand for higher bearing capacity in the steel pipe piles and concrete piles that constitute the foundation structures of these buildings and facilities.

[0003] Incidentally, when driving steel pipe piles or concrete piles into hard ground, a method is employed in which drilling is performed using an excavation auger before driving the steel pipe piles. Drilling generally takes various forms, such as drilling to hard ground located relatively deep underground, or drilling to intermediate depths of ground that do not reach the hard ground.

[0004] In either configuration, between drilling and the installation of steel pipe or concrete piles, it may be necessary to preserve the drilled section for a certain period of time due to coordination with other processes. However, since drilled sections create hollow spaces in the ground, there is a concern that if these are left as they are, the hollow spaces in the ground may cause instability in the drilled section and the surrounding ground. Therefore, it is necessary to prevent ground instability by temporarily injecting a ground stabilizing material, such as backfill material, into the drilled section between drilling and the installation of steel pipe or concrete piles.

[0005] Cement grout is sometimes used as a ground stabilization material. The cement grout injected into the borehole is mixed with the in-situ soil to form soil cement, which allows the borehole to be held stably.

[0006] However, cement can contain hexavalent chromium. If this hexavalent chromium leaches from soil cement into the ground, it can cause environmental problems. Furthermore, if the soil cement formed in the ground hardens and becomes highly strong, the soil cement itself may become an obstacle to subsequent steel pipe pile or concrete pile driving, potentially causing delays in the construction period. Moreover, re-drilling ground containing hardened soil cement that has become stronger than necessary requires drilling with more powerful power, which may induce ground instability. In addition, since cement has a high carbon dioxide emission rate during its manufacture, there is a growing need to reduce the amount of cement used in cement grout from the perspective of protecting the global environment.

[0007] Herein, Patent Document 1 describes a slurry composition for ground improvement comprising cement, water and an admixture, wherein the following blast furnace cement is used as the cement and the following admixture is used as the admixture, the mass ratio of water to the blast furnace cement is adjusted to 40 to 250%, and the admixture is contained in a ratio of 0.1 to 5 parts by mass per 100 parts by mass of the blast furnace cement. Blast furnace cement: Fineness of 3000-13000 cm² 2 A blast furnace cement comprising 64-76% by mass of blast furnace slag fine powder and Portland cement, wherein the blast furnace slag fine powder is present in a ratio of 64-76% by mass and the Portland cement in a ratio of 24-36% by mass (total 100% by mass). Admixture: An admixture containing the following fluidizing agent, curing accelerator, and defoaming agent. Flowing agent: One or more selected from alkali metal salts of water-soluble vinyl copolymers with a mass-average molecular weight of 2,000 to 70,000 obtained by alkali hydrolysis of a copolymer of α-olefin and maleic anhydride, and alkali metal salts of polyacrylic acid with a mass-average molecular weight of 1,500 to 50,000. Curing accelerator: Alkali metal carbonate Antifoaming agent: Polyalkylene glycol monoalkenyl ether

[0008] Furthermore, Patent Document 2 describes a pile-surrounding filling liquid comprising water added to a cement-based binder, wherein the cement is blast furnace cement type B, the binder contains 7% to 9% by weight of anhydrous gypsum as an industrial by-product relative to its weight, and the water-to-binder ratio is 80-100%.

[0009] However, the ground improvement slurry composition described in Patent Document 1 is used for ground improvement purposes in earth retention work, underground waterproofing work, soft ground improvement work, etc. Furthermore, the pile perimeter filling liquid described in Patent Document 2 is used to fill the area around pre-fabricated piles to increase friction with the ground. Therefore, Patent Documents 1 or 2 do not consider the fact that the strength of the hardened soil cement may hinder subsequent steel pipe pile driving or concrete pile driving, or induce ground instability during re-drilling. [Prior art documents] [Patent Documents]

[0010] [Patent Document 1] Patent No. 5545678 [Patent Document 2] Patent No. 4546313 [Overview of the project] [Problems that the invention aims to solve]

[0011] The present invention has been made in view of the above circumstances, and aims to provide a ground stabilization method that suppresses the leaching of hexavalent chromium, keeps the strength of the hardened soil cement relatively low, and reduces the amount of cement used. Furthermore, the present invention aims to provide a pile driving method that suppresses the leaching of hexavalent chromium, facilitates re-drilling of soil containing hardened soil cement, and reduces the amount of cement used. [Means for solving the problem]

[0012] In order to solve the above problems, the present invention adopts the following configuration. [1] A step of forming soil cement by injecting a ground stabilizer containing cement into an excavation hole formed in the ground and stirring and mixing the ground stabilizer and the in-situ soil is provided. The ground stabilizer contains a solidifying material composed of blast furnace slag fine powder having a specific surface area of 3000 cm 2 / g to 10000 cm 2 / g, water, and a admixture, The cement is any one of ordinary Portland cement, low heat Portland cement, or moderate heat Portland cement. A ground stabilization method that satisfies the following formulas (i) to (iii). 30 ≦ C / (C + GGBFS)×100 ≦ 70 …(i) 150 ≦ W / (C + GGBFS)×100 ≦ 270 …(ii) 0 ≦ SP / (C + GGBFS)×100 ≦ 5 …(iii) However, in formulas (i) to (iii), C is the mass (kg) of cement, GGBFS is the mass (kg) of blast furnace slag fine powder, W is the mass (kg) of water, and SP is the mass (kg) of the admixture. [2] The ground stabilization method according to [1], wherein the addition amount of the solidifying material with respect to 1.0 m of in-situ soil is 50 to 300 kg. 3 [3] The ground stabilization method according to [1], wherein the admixture (SP) is a chemical admixture containing one or more of lignin sulfonate, oxycarboxylate, polycarboxylate, or silicofluoride. [4] At the construction site, the ground stabilizer is prepared by kneading the cement, the blast furnace slag fine powder, the water, and the admixture, and the prepared ground stabilizer is injected into the excavation hole formed in the ground. The ground stabilization method according to [1]. [5] Using blast furnace cement as the cement, The ground stabilization method described in [4], wherein the amount of blast furnace cement and the amount of blast furnace slag powder are adjusted so that the total amount of blast furnace slag contained in the blast furnace cement and the mixing ratio of the blast furnace cement to the cement contained in the blast furnace cement satisfies the following formula (iv) instead of formula (i). 30≦C' / (C'+GGBFS')×100≦70 …(iv) However, in formula (iv), C' is the mass (kg) of cement contained in the blast furnace cement, and GGBFS' is the total amount (kg) of blast furnace slag fine powder and blast furnace slag contained in the blast furnace cement. A pile driving method comprising: re-drilling into the ground containing hardened soil cement formed in the excavation hole by the ground stabilization method described in any one of items [1] to [5] to form a new excavation hole; and driving a steel pipe pile or concrete pile into the new excavation hole. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a ground stabilization method that suppresses the leaching of hexavalent chromium, keeps the strength of the hardened soil cement relatively low, and reduces the amount of cement used. Furthermore, according to the present invention, it is possible to provide a pile driving method that suppresses the leaching of hexavalent chromium, facilitates re-drilling of the soil containing soil cement after hardening, and reduces the amount of cement used. [Brief explanation of the drawing]

[0014] [Figure 1] A schematic cross-sectional diagram illustrating a ground stabilization method, which is an embodiment of the present invention. [Figure 2] A schematic cross-sectional diagram illustrating a ground stabilization method, which is an embodiment of the present invention. [Figure 3] A schematic cross-sectional diagram illustrating a pile driving method according to an embodiment of the present invention. [Figure 4] A schematic cross-sectional diagram illustrating a pile driving method according to an embodiment of the present invention. [Modes for carrying out the invention]

[0015] When constructing steel pipe piles or concrete piles, it is sometimes necessary to preserve the drilled area between drilling and the installation of the steel pipe piles or concrete piles. As a means of achieving this, ground stabilization materials such as backfill material are injected into the drilled area.

[0016] The inventors of the present invention have diligently studied ground stabilization materials that can be used for such applications, which can suppress the leaching of hexavalent chromium into the ground, keep the soil cement formed by mixing the ground stabilization material with in-situ soil to a relatively low strength, and reduce the amount of cement used in the ground stabilization material.

[0017] As a result, the above problems can be solved by replacing a portion of the cement with blast furnace slag fine powder and optimizing the amount of water, thus completing the present invention. Furthermore, it has become clear that, according to the present invention, material segregation does not occur after the construction of the ground stabilization material, and the material can exhibit the necessary performance as a ground stabilization material. The following describes the ground stabilization method and pile driving method, which are embodiments of the present invention.

[0018] The ground stabilization method of this embodiment includes the step of injecting a ground stabilization material containing cement into an excavated hole formed in the ground, and forming soil cement by stirring and mixing the ground stabilization material with in-situ soil, wherein the ground stabilization material contains cement and 3000 cm 2 / g~10000cm 2 This is a ground stabilization method that contains a solidifying agent consisting of blast furnace slag fine powder with a specific surface area of ​​ / g, water, and an admixture, wherein the cement is either ordinary Portland cement, low-heat Portland cement, or moderate-heat Portland cement, and satisfies the following formulas (i) to (iii). 30≦C / (C+GGBFS)×100≦70 …(i) 150≦W / (C+GGBFS)×100≦270…(ii) 0≦SP / (C+GGBFS)×100≦5 …(iii) However, in equations (i) to (iii), C is the mass of cement (kg), GGBFS is the mass of blast furnace slag powder (kg), W is the mass of water (kg), and SP is the mass of the admixture (kg).

[0019] Furthermore, the pile driving method of this embodiment is a pile driving method in which a new excavation hole is formed by re-drilling into the ground containing hardened soil cement formed in the excavation hole by the above-described ground stabilization method, and a steel pipe pile or concrete pile is driven into the new excavation hole.

[0020] In the ground stabilization method of this embodiment, first, as shown in Figure 1, a borehole 1 is formed by pre-drilling into the ground G1. For example, the earth auger drilling method can be applied for the pre-drilling. The earth auger drilling method uses an auger screw with an auger head attached to its tip to drill into the ground G1. This creates a borehole 1 in the ground G1. There are no particular restrictions on the depth of the borehole 1, and as shown in Figure 1, it may be made to penetrate an intermediate layer G2 that includes underground obstacles or hard ground. Note that in-situ soil, not shown, which has been agitated by drilling, remains in the borehole 1.

[0021] Next, as shown in Figure 2, the ground stabilizing material according to this embodiment is injected into the borehole 1, and then mixed with the remaining in-situ soil to form soil cement 2. The injection of the ground stabilizing material and mixing with the in-situ soil may be performed, for example, by supplying the ground stabilizing material into the ground from the auger head while raising the auger screw that was inserted into the ground during the preliminary drilling, and mixing the ground stabilizing material with the in-situ soil by the rotating auger head.

[0022] Thus, in the ground stabilization method of this embodiment, when it is necessary to preserve the excavation hole 1 between the time of initial drilling and the time of driving the steel pipe piles, soil cement 2 is formed inside the excavation hole 1 and hardened to form a soil cement column. This stabilizes the ground in and around the excavation hole 1 and preserves the excavation hole.

[0023] Next, in the pile driving method of this embodiment, as shown in Figure 3, a re-drilled hole 3 is created in the ground G1 containing the hardened soil cement 2 by re-drilling. The formation of the re-drilled hole 3 can be done in the same way as in the case of the initial drilling, for example, by applying the earth auger drilling method. The position of the re-drilled hole 3 is approximately the same as the position of the drilled hole 1 created by the initial drilling. Since the drilled hole 1 is filled with soil cement 2, the re-drilling will excavate at least the soil cement.

[0024] The re-drilling may be performed to the same depth as the initial drilling or to a deeper depth than the initial drilling, that is, to drill through the entire soil cement. Alternatively, the re-drilling may be performed to a shallower depth than the initial drilling, that is, to drill in a way that leaves a portion of the soil cement intact.

[0025] Next, as shown in Figure 4, a steel pipe pile 5 is driven into the re-excavated hole 3. Alternatively, a concrete pile may be driven instead of the steel pipe pile 5.

[0026] Furthermore, when constructing the steel pipe pile 5, an expanded base reinforcement section may be formed at the tip of the steel pipe pile 5 to constitute a tip-base reinforced and expanded-base pile. Alternatively, before driving the steel pipe pile 5 or concrete pile, soil cement slurry may be injected into the re-excavated hole 3, and then the steel pipe pile 5 or concrete pile may be driven to constitute a soil cement pile.

[0027] Next, the ground stabilization material applied to the ground stabilization method and pile driving method of this embodiment will be described.

[0028] The ground stabilizing material of this embodiment is composed of a solidifying agent, water, and an admixture. Note that the admixture may not be included in the ground stabilizing material. The composition of the ground stabilizing material is described below.

[0029] The solidifying agent is cement and 3000 cm 2 / g~10000cm 2 It consists of blast furnace slag fine powder with a specific surface area of ​​ / g. It consists of cement and blast furnace slag fine powder.

[0030] For the cement, for example, any one of ordinary Portland cement, low heat Portland cement or moderate heat Portland cement can be used.

[0031] The fine powder of blast furnace slag is obtained by rapidly cooling the molten slag formed simultaneously with pig iron in a blast furnace with water to obtain water - quenched slag and then pulverizing the water - quenched slag. By blending the fine powder of blast furnace slag into the ground stabilizer, the curing reaction of soil cement can be suppressed, the curing rate can be reduced, and the high - strength improvement of the soil cement after curing can be prevented. Also, by substituting a part of the cement with the fine powder of blast furnace slag, the elution value of hexavalent chromium into the ground G1 can be suppressed.

[0032] In this embodiment, as the fine powder of blast furnace slag, those with a specific surface area in the range of 3000 cm 2 / g to 10000 cm 2 / g are used. When the specific surface area is less than the lower limit value, the curing reaction of soil cement is significantly suppressed, the curing rate decreases, and the curing time until the desired hardness is reached becomes long, which may cause problems such as material separation, so it is not preferable. Also, when the specific surface area exceeds the upper limit value, the curing of soil cement progresses rapidly, and the strength of the soil cement rises excessively, so it is not preferable.

[0033] The blending ratio of cement in the amount of the solidifying agent (total amount of cement and fine powder of blast furnace slag) in the ground stabilizer needs to satisfy the following formula (i).

[0034] 30≦C / (C + GGBFS)×100≦70 …(i)

[0035] In formula (i), C is the mass (kg) of cement, and GGBFS is the mass (kg) of the fine powder of blast furnace slag.

[0036] If C / (C+GGBFS)×100 is less than 30, that is, if the ratio of cement to the total amount of cement and blast furnace slag fine powder is less than 30%, the hardening rate of the soil cement will decrease, the hardening time to reach the desired hardness will increase, and there is a risk of problems such as material separation, which is undesirable. On the other hand, if C / (C+GGBFS)×100 exceeds 70, that is, if the ratio of cement to the total amount of cement and blast furnace slag fine powder exceeds 70%, there will be an excess of cement, and the amount of hexavalent chromium leached from the soil cement into the ground G1 will increase, which is undesirable. The range of C / (C+GGBFS)×100 may be greater than 36 and 90 or less, 40 or more and 80 or less, or 50 or more and 70 or less.

[0037] Water enhances the fluidity of the ground stabilization material and also affects the hardness of the soil cement after hardening; therefore, the amount of water used in this embodiment is an important factor. The ratio of water to the amount of solidifying agent (total amount of cement and blast furnace slag powder) in the ground stabilization material must satisfy the following formula (ii).

[0038] 150≦W / (C+GGBFS)×100≦270…(ii)

[0039] In equation (ii), C is the mass of cement (kg), GGBFS is the mass of blast furnace slag powder (kg), and W is the mass of water (kg).

[0040] If W / (C+GGBFS)×100 is less than 150, that is, if the ratio of water to the total amount of cement and blast furnace slag powder is less than 150%, the fluidity of the ground stabilizing material decreases, sufficient mixing with the in-situ soil does not proceed, and it becomes impossible to form soil-cement columns with a uniform composition, resulting in variations in strength, which is undesirable. On the other hand, if W / (C+GGBFS)×100 exceeds 270, that is, if the ratio of water to the total amount of cement and blast furnace slag powder exceeds 270%, there is an excess of water, the strength of the soil-cement columns after hardening decreases significantly, and the ground cannot be sufficiently stabilized. The range of W / (C+GGBFS)×100 may be 170 or more and 230 or less, or 200 or more and 220 or less.

[0041] In this embodiment, the admixture may be formulated primarily for the purpose of reducing the hardening rate of the soil cement. Alternatively, the admixture may be formulated for the purpose of improving fluidity. Furthermore, the admixture may be formulated for the purpose of reducing the amount of water while maintaining fluidity.

[0042] The mixing ratio of admixture to the amount of solidifying agent (total amount of cement and blast furnace slag powder) in the ground stabilization material must satisfy the following formula (iii).

[0043] 0≦SP / (C+GGBFS)×100≦5 …(iii)

[0044] In equation (iii), C is the mass of cement (kg), and GGBFS is the mass of blast furnace slag powder (kg).

[0045] SP / (C+GGBFS)×100 may be 0, but it may be 0.1 or greater in order to obtain the desired effect of the admixture. That is, if the mixing ratio of the admixture to the total amount of cement and blast furnace slag fine powder is 0.1% or more, the effects of the admixture in reducing the hardening speed, improving fluidity, and reducing the amount of water can be fully exerted. On the other hand, if SP / (C+GGBFS)×100 exceeds 5, that is, if the mixing ratio of the admixture to the total amount of cement and blast furnace slag fine powder exceeds 5%, the effect of adding the admixture becomes saturated. The range of SP / (C+GGBFS)×100 may be 0.1 or more, or 0.2 or more and 4 or less, or 0.5 or more and 3 or less, or 1 or more and 2 or less.

[0046] The admixture is more preferably a chemical admixture containing one or more of lignin sulfonates, oxycarboxylates, polycarboxylates, or silicoids. By using the above chemical admixture as the admixture, the hardening rate of the soil cement can be reduced, and the strength of the soil cement after hardening can be prevented from becoming excessively high.

[0047] Furthermore, as a mixing agent, the above-mentioned chemical admixtures may be replaced with, or together with, AE agents, high-performance water-reducing agents, AE water-reducing agents, fluidizing agents, etc.

[0048] Furthermore, the ground stabilization material can also contain additives. Examples of additives include pozzolanic materials, hydraulic alumina components, hydraulic additives such as ultrafast-setting cement or gypsum, and lime components such as quicklime, slaked lime, lightly calcined dolomite, or hydroxide dolomite. By adding these, the ground stabilization material can be suitably used even if the soil type of the ground is high-organic soil, sludge, or other special soils.

[0049] In this embodiment, 1.0 m of in-situ soil is used. 3It is preferable to add 50 to 300 kg of solidifying agent (cement and blast furnace slag fine powder) to the soil. By adding 50 kg or more, it is possible to ensure sufficient volume of soil cement after hardening without insufficient soil stabilization material relative to the in-situ soil, thereby stabilizing the ground. Alternatively, by adding 300 kg or less, it is possible to ensure the strength of the soil cement, stabilize the ground, and suppress the leaching of hexavalent chromium into the ground G1.

[0050] In this embodiment, it is preferable to prepare the ground stabilization material at the construction site of the steel pipe pile or concrete pile. Specifically, it is preferable to prepare the ground stabilization material at the construction site by mixing cement, blast furnace slag powder, water, and pre-admixture, and then inject the prepared ground stabilization material into the excavated hole in the ground.

[0051] Furthermore, when preparing the ground stabilization material, blast furnace cement can be used as the cement. In this case, it is preferable to adjust the proportions of blast furnace cement and blast furnace slag powder so that the total amount of blast furnace slag powder and blast furnace slag contained in the blast furnace cement, and the proportion of cement contained in the blast furnace cement, satisfy formula (iv) below, instead of formula (i) above. The reason for limiting formula (iv) is the same as in the case of formula (i).

[0052] 30≦C' / (C'+GGBFS')×100≦70 …(iv)

[0053] In equation (iv), C' is the mass (kg) of cement contained in the blast furnace cement, and GGBFS' is the total amount (kg) of blast furnace slag fine powder and blast furnace slag contained in the blast furnace cement.

[0054] The ground stabilization material used in this embodiment is injected into ground G1 after preliminary drilling to stabilize the ground at the drilled site. After the injection of the ground stabilization material, it is mixed with the in-situ soil and then hardens to form soil-cement columns, stabilizing the ground at the drilled site. This type of ground stabilization treatment is carried out as an intermediate step in pile driving after drilling of ground G1, and after a predetermined time has elapsed, the ground that has been stabilized is drilled again and piles are driven. In this way, for ground stabilization materials used as an intermediate step in pile driving, it is desirable that the formed soil-cement exhibits the following performance characteristics due to its construction characteristics.

[0055] [Uniaxial compressive strength of soil cement at 28 days of age: 10-1550 kN / m 2 ] The unconfined compressive strength of the soil cement, measured in accordance with JIS A 1216:2020 "Unconfined Compression Test Method for Soil," is preferably 100 to 1550 kN / m². 2 And more preferably 200-1550 kN / m 2 It is preferable that the strength is within the low strength range described above. If the strength is too high, it will hinder subsequent re-drilling processes, while if the strength is too low, the ground G1 cannot be effectively stabilized.

[0056] [Hexavalent chromium elution level: 0.05 mg / L or less] After the soil-cement columns are formed in the ground, hexavalent chromium contained in the cement must not leach into the surrounding ground beyond the specified limit. Therefore, the hexavalent chromium leaching value, measured in accordance with "Environmental Notification No. 46 Test," must be kept below 0.05 mg / L.

[0057] As explained above, according to the ground stabilization method of this embodiment, since blast furnace slag fine powder is incorporated into the ground stabilization material by substituting a portion of the cement, it can suppress the leaching of hexavalent chromium, an environmentally harmful substance, and reduce the risk of environmental pollution. Furthermore, since the unconfined compressive strength of the ground stabilization material after hardening is kept in the low strength range, it does not hinder subsequent re-drilling processes and provides performance that enables ground stabilization treatment. In addition, from the viewpoint of CO2 emissions, CO2 emissions can be kept low by using blast furnace slag fine powder as a substitute for cement.

[0058] Furthermore, by adjusting the blending ratio of blast furnace slag fine powder to an appropriate range, the leaching of hexavalent chromium derived from cement can be effectively suppressed. Furthermore, by setting the water-binding ratio (W / (C+GGBFS)) to 150-270%, it is possible to ensure the strength of the soil cement and the fluidity (viscosity) of the ground stabilization material necessary for the ground stabilization method. Furthermore, the desired effect can be achieved by mixing the admixture with the binder (C+GGBFS) at a ratio of 5.0% or less. Furthermore, by using either ordinary Portland cement, low-heat Portland cement, or moderate-heat Portland cement, and partially substituting these cements with blast furnace slag powder, appropriate hardening delay, strength development, and fluidity (viscosity) can be achieved. The specific surface area related to the reactivity of blast furnace slag powder is 3000-10000 cm². 2 Anything within the range of / g is acceptable. Due to the above characteristics, the ground can be stabilized by injecting a ground stabilization material into the ground after pre-drilling.

[0059] Furthermore, according to the ground stabilization method of this embodiment, 1 m of in-situ soil 3 By adding 50 to 300 kg of solidifying agent, the soil cement can be mixed with the in-situ soil while maintaining fluidity, and then hardened. The hardened soil cement has a moderately low strength, making it easy to re-drill.

[0060] Furthermore, according to the ground stabilization method of this embodiment, by using a chemical admixture whose main components are one or more of polycarboxylic acids, ligninsulfonic acid, oxycarboxylic acids, or silicogenic compounds, particularly effective performance can be achieved in terms of fluidity and strength.

[0061] Furthermore, according to the ground stabilization method of this embodiment, by mixing the ground stabilization material at the construction site, it is possible to mix a ground stabilization material that is suitable for the detailed soil conditions of the site, which become clear during the construction phase, and to carry out construction using a ground stabilization material that is more appropriate for the ground at the site.

[0062] Furthermore, according to the pile driving method of this embodiment, when re-drilling in areas where the ground stabilization method of this embodiment has been implemented, the soil cement is kept at a low strength, resulting in good workability during re-drilling. In addition, since the surrounding ground is also in a stable state, the structural performance exhibited after the steel pipe piles or concrete piles are driven will also be more stable. [Examples]

[0063] The present invention will be specifically described below with reference to examples. At an ambient temperature of 20°C, ground stabilization materials No. 1 to 26 shown in Table 1A were manufactured by mixing cement, blast furnace slag powder, water, and admixtures in predetermined proportions. The blast furnace slag powder had a surface area of ​​4100 cm². 2 The product used was one containing 1g of material. Ordinary Portland cement was used. The admixtures used were chemical admixtures with the compositions shown in Table 2 below.

[0064] Next, soil cement was created by mixing in-situ soil with ground stabilization materials No. 1 to 26, including sandy soil (simulated soil), cohesive soil (simulated soil), and soil collected from the Kanto loam layer (collected from the construction site). 1 m of in-situ soil 3 The amount of solidifying agent added per unit was set at 300 kg or 100 kg. Bentonite (B) was added only when the soil type was sandy, and per 1 m³ of in-situ soil. 320 kg was added per unit. For sandy soil, silica sand and kaolinite clay were mixed in a mass ratio of silica sand:kaolinite clay = 9:1. For clayey soil, kaolinite clay was used.

[0065] The obtained soil cement was cured by sealing at a temperature of 20°C and a humidity of 90% or higher. The unconfined compressive strength at 7 days and 28 days of age, as well as the hexavalent chromium leaching value at 7 days and 28 days of age, were measured for the cured soil cement. The measurement methods were as described above. The results are shown in Table 1B.

[0066] Table 1B shows the CO2 emissions during the manufacturing of each concrete composition. These CO2 emissions were calculated using the following formula (A), assuming CO2 intensity for cement and blast furnace slag powder were 755.5 kg-CO2 / t and 40.21 kg-CO2 / t, respectively. The CO2 intensity for cement is based on the cement variety inventory data list in "Overview of LCI Data for Cement," published April 1, 2024, by the Japan Cement Association. The CO2 intensity for blast furnace slag powder is based on the Japan Concrete Institute's Research Committee Report on Environmental Impact Assessment of Cement and Concrete, published September 2024. Bentonite was not considered because its addition amount was very small and its impact on CO2 intensity was expected to be small.

[0067] CO2 emissions from concrete composition (kg / m³) 3 ) = {755.5 × cement mix ratio (kg / m 3 ) + 40.21 × amount of blast furnace slag fine powder added (kg / m³ 3 ) + 7.09 x aggregate content (kg / m 3 )} / 1000 …(A)

[0068] [Table 1A]

[0069] [Table 1B]

[0070] [Table 2]

[0071] As shown in Tables 1A and 1B, samples No. 1, 2, 4, 5, 7-11, 13, and 15-26, which contain blast furnace slag fine powder, all satisfy the specified performance values, indicating that suitable ground stabilization materials for ground stabilization methods are provided. 3 CO2 emissions per unit area are 200 kg / m³ 3 The results are as follows: Compared to samples No. 3, 6, 12, and 14, which did not contain blast furnace slag powder, replacing a portion of the cement with blast furnace slag powder made it possible to reduce CO2 emissions during the production of the ground stabilizing material, thus contributing to the preservation of the global environment.

[0072] On the other hand, samples No. 3, 6, 12, and 14, which did not contain blast furnace slag powder, showed slightly higher levels of hexavalent chromium leaching, and the ground stabilization material 1m 3 CO2 emissions per unit area are 200 kg / m³ 3 They all exceeded this value, indicating high levels.

[0073] Based on the above results, it was found that the ground stabilization material of the present invention can exhibit excellent performance. [Explanation of Symbols]

[0074] 1…Drilled hole 2…Soil cement 3…Re-excavated hole 5…Steel pipe pile G1…Ground G2…Middle layer

Claims

1. The process includes injecting a ground stabilizing material containing cement into a borehole formed in the ground, and then mixing the ground stabilizing material with in-situ soil to form soil cement. The aforementioned ground stabilizing material is made of cement and 3000 cm ２ / g~10000cm ２ It contains a solidifying agent consisting of blast furnace slag fine powder with a specific surface area of ​​1 / g, water, and an admixture. The cement is either ordinary Portland cement, low-heat Portland cement, or moderate-heat Portland cement. A ground stabilization method that satisfies equations (i) through (iii) below. 30≦C / (C+GGBFS)×100≦70…(i) 150≦W / (C+GGBFS)×100≦270…(ii) 0≦SP / (C+GGBFS)×100≦5…(iii) However, in equations (i) to (iii), C is the mass of cement (kg), GGBFS is the mass of blast furnace slag powder (kg), W is the mass of water (kg), and SP is the mass of the admixture (kg).

2. In-situ soil 1.0m ３ The ground stabilization method according to claim 1, wherein the amount of the solidifying agent added to is 50 to 300 kg.

3. The ground stabilization method according to claim 1, wherein the admixture (SP) is a chemical admixture containing one or more of lignin sulfonates, oxycarboxylic acid salts, polycarboxylic acid salts, or silicogenic compounds.

4. The ground stabilization method according to claim 1, comprising: preparing the ground stabilizing material at the construction site by mixing the cement, the blast furnace slag fine powder, the water, and the admixture; and injecting the prepared ground stabilizing material into the excavated hole formed in the ground.

5. Blast furnace cement is used as the aforementioned cement. The ground stabilization method according to claim 4, wherein the blending ratio of the blast furnace cement and the blast furnace slag powder is adjusted so that the total amount of blast furnace slag contained in the blast furnace cement and the cement contained in the blast furnace cement satisfy formula (iv) below instead of formula (i). 30≦C' / (C'+GGBFS')×100≦70...(iv) However, in formula (iv), C' is the mass (kg) of cement contained in the blast furnace cement, and GGBFS' is the total amount (kg) of blast furnace slag fine powder and blast furnace slag contained in the blast furnace cement.

6. A pile driving method comprising: re-drilling into the ground containing hardened soil cement formed in the excavation hole by the ground stabilization method described in any one of claims 1 to 5 to form a new excavation hole; and driving a steel pipe pile or a concrete pile into the new excavation hole.

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