Steel pipe soil cement piles and their construction method

Abstract

This invention provides a steel pipe soil-cement pile and a construction method that can reduce the amount of cement used by suppressing the leaching of hexavalent chromium, while also reducing the pile's resistance to penetration into the soil-cement. [Solution] The system comprises a steel pipe (2) and a pile-circumferential soil cement (5), wherein the pile-circumferential soil cement (5) consists of soil cement containing cement milk, and the cement milk contains cement and 3000 cm 2 / g or more 10000cm 2 A steel pipe soil cement pile (1) is adopted, which contains a solidifying agent consisting of blast furnace slag fine powder having a specific surface area of ​​less than / g, water, and an admixture, and the soil cement (5) filling the pile perimeter has a different composition in the general pile section (3a) and the pile tip section (4a), and the cement is either ordinary Portland cement, low-heat Portland cement, or moderate-heat Portland cement.

Description

[Technical Field]

[0001] The present invention relates to steel pipe soil cement piles and methods for constructing them. [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 that constitute the foundation structures of these buildings and facilities.

[0003] Incidentally, when driving piles into hard ground, a construction method is employed in which pre-drilling is performed using an excavation auger, followed by the driving of steel pipe piles. In such construction methods, when the hard ground is in the intermediate layer, or when the supporting layer is deep and it is desired to stabilize the steel pipe pile foundation as a friction pile, a high circumferential friction force is required. In such cases, the steel pipe soil cement pile construction method is particularly effective, in which pile circumferential filling liquid (cement milk) is filled into the steel pipe and the ground, mixed with the in-situ soil to form soil cement, and the soil cement is hardened.

[0004] However, cement in cement grout may contain hexavalent chromium. If this hexavalent chromium leaches from the soil cement into the ground, it can trigger environmental problems. In addition, after the cement is injected into the ground, it is mixed with the in-situ soil and hardens, but if the steel pipe installation work is delayed due to weather problems or equipment problems, the hardening of the soil cement may progress, making it difficult to install the steel pipes. Furthermore, in recent years, from the perspective of protecting the global environment, the need to reduce the amount of cement used, which emits a large amount of CO2 during its manufacture, has been raised.

[0005] 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

[0006] Furthermore, Patent Document 2 describes a pile-surrounding filling liquid (cement milk) made by adding water 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%.

[0007] However, the slurry composition for ground improvement described in Patent Document 1 is used for ground improvement in mountain retaining work, underground water stopping work, soft ground improvement work, etc. Further, the pile circumferential filling liquid described in Patent Document 2 is used for the purpose of filling the circumferential portion of an existing pile to increase the friction with the ground. Thus, Patent Documents 1 and 2 are not related to the construction of steel pipe soil-cement piles. Therefore, in the construction of steel pipe soil-cement piles, the difficulty of sinking the steel pipe into the soil-cement, or in other words, the pile penetration resistance against the soil-cement, has not been studied at all.

Prior Art Documents

Patent Documents

[0008]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0009] The present invention has been made in view of the above circumstances, and an object thereof is to provide a steel pipe soil-cement pile and a construction method thereof that can reduce the pile penetration resistance into soil-cement while suppressing the elution of hexavalent chromium and reduce the amount of cement used.

Means for Solving the Problems

[0010] In order to solve the above problems, the present invention adopts the following configuration. (1) A steel pipe soil-cement pile comprising a steel pipe buried in the ground and soil-cement for filling around the steel pipe, wherein the soil-cement for filling around the pile consists of soil-cement containing cement milk, and the cement milk is composed of cement and 3000 cm 2 / g or more and 10000 cm 2It contains a solidifying agent consisting of blast furnace slag fine powder with a specific surface area of ​​less than / g, water, and an admixture. The aforementioned pile-filling soil cement satisfies the following formulas (i), (ii), and (iii): A steel pipe soil cement pile, wherein the cement used is either ordinary Portland cement, low-heat Portland cement, or moderate-heat Portland cement. 30≦C / (C+GGBFS)×100≦70…(i) 80≦W / (C+GGBFS)×100≦160…(ii) 0.1≦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) The aforementioned steel pipe soil cement pile is divided into a pile tip portion and a general pile portion located above ground level than the pile tip portion. The pile-filling soil cement formed in the general portion of the pile satisfies formulas (i), (ii), and (iii). The pile tip filling cement formed at the pile tip satisfies formulas (i), (iii) and formula (iv) below, as described in (1), for the steel pipe soil cement pile. 45≦W / (C+GGBFS)×100≦110…(iv) However, in equation (iv), 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). (3) In the aforementioned soil cement, 1.0 m of in-situ soil 3 The amount of the solidifying agent mixed per unit area is In the general pile section, the weight is between 100 kg and 500 kg. The steel pipe soil cement pile according to (2), characterized in that the pile tip weighs between 800 kg and 1200 kg. (4) The steel pipe soil cement pile according to (1) or (2), wherein the admixture (SP) is a chemical admixture containing a lignin sulfonate, an oxycarboxylate, a polycarboxylate, or a silicoid. (5) The steel pipe soil cement pile according to (1) or (2), characterized in that the steel pipe is a steel pipe with external protrusions. (6) A method for constructing steel pipe soil cement piles, in which soil cement is formed around a steel pipe buried in the ground, The aforementioned pile perimeter filling soil cement is formed by soil cement containing cement milk, The aforementioned cement milk is made of cement and 3000 cm 2 / g or more 10000cm 2 It contains a solidifying agent consisting of blast furnace slag fine powder with a specific surface area of ​​less than / g, water, and an admixture. The aforementioned pile-filling soil cement satisfies the following formulas (i), (ii), and (iii): A method for constructing steel pipe soil cement piles, wherein the cement used is either ordinary Portland cement, low-heat Portland cement, or moderate-heat Portland cement. 30≦C / (C+GGBFS)×100≦70…(i) 80≦W / (C+GGBFS)×100≦160…(ii) 0.1≦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). (7) The aforementioned steel pipe soil cement pile is divided into a pile tip portion and a general pile portion located above ground level than the pile tip portion. The pile-filling soil cement formed in the general portion of the pile satisfies formulas (i), (ii), and (iii). The construction method for steel pipe soil cement piles described in (6), wherein the pile tip filling cement formed at the pile tip satisfies formulas (i), (iii) and formula (iv) below. 45 ≦ W / (C + GGBFS) × 100 ≦ 110 …(iv) However, in formula (iv), C is the mass of cement (kg), GGBFS is the mass of ground granulated blast - furnace slag powder (kg), and W is the mass of water (kg). (8) In the construction method of the soil - cement pile, the blending amount of the solidifying agent per 1.0 m 3 of the in - situ soil is 800 kg or more and 1200 kg / m 3 at the tip of the pile, and 100 kg or less and 500 kg / m 3 at the general part of the pile. The construction method of the steel - pipe soil - cement pile according to (7) is characterized by this. (9) The admixture (SP) is a chemical admixture containing lignin sulfonate, oxycarboxylate, polycarboxylate or silicofluoride. The construction method of the steel - pipe soil - cement pile according to (6) or (7). (10) The steel pipe is a steel pipe with protrusions on the outer surface. The construction method of the steel - pipe soil - cement pile according to (6) or (7) is characterized by this. (11) At the construction site of the steel - pipe soil - cement pile, the cement milk is prepared by kneading the solidifying agent, the water and the admixture, and the prepared cement milk is supplied around the steel pipe buried in the ground. The construction method of the steel - pipe soil - cement pile according to (6) or (7). (12) Using blast - furnace cement as the cement, The blending amount of the blast - furnace cement and the ground granulated blast - furnace slag powder is adjusted so that the mixing ratio of the total amount of the blast - furnace slag contained in the ground granulated blast - furnace slag powder and the blast - furnace cement and the cement contained in the blast - furnace cement satisfies the following formula (v) instead of the formula (i). The construction method of the steel - pipe soil - cement pile according to (11). 30 ≦ C’ / (C’ + GGBFS’) × 100 ≦ 70 …(v) However, in equation (v), 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. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a steel pipe soil cement pile and a method for constructing it that can reduce the amount of cement used while suppressing the leaching of hexavalent chromium and reducing the resistance of the pile to penetration into the soil cement. [Brief explanation of the drawing]

[0012] [Figure 1] This is a cross-sectional view of a steel pipe soil cement pile after construction is completed according to an embodiment of the present invention. [Figure 2] This is a schematic cross-sectional view showing one step in the first construction example according to an embodiment of the present invention. [Figure 3] This is a schematic cross-sectional view showing the next step following the process in Figure 2. [Figure 4] This is a schematic cross-sectional view showing the next step following the process shown in Figure 3. [Figure 5] This is a schematic cross-sectional view showing the next step following the process in Figure 4. [Figure 6] This is a schematic cross-sectional view showing the next step following the process in Figure 5. [Figure 7] This is a schematic cross-sectional view showing one step in a second construction example according to an embodiment of the present invention. [Figure 8] This is a schematic cross-sectional view showing the next step following the process shown in Figure 7. [Figure 9] This is a schematic cross-sectional view showing the next step following the process in Figure 8. [Figure 10] This is a schematic cross-sectional view showing the next step following the process in Figure 9. [Figure 11] This is a schematic cross-sectional view showing the next step following the process in Figure 10. [Figure 12] This is a schematic cross-sectional view showing the next step following the process in Figure 11. [Modes for carrying out the invention]

[0013] [Steel pipe soil cement piles] The steel pipe soil cement 1 of this embodiment comprises a steel pipe buried in the ground and pile-circumferential soil cement formed around the steel pipe. The aforementioned pile-filling soil cement consists of soil cement containing cement milk. The aforementioned cement milk is made of cement and 3000 cm 2 / g or more 10000cm 2 It contains a solidifying agent consisting of blast furnace slag fine powder with a specific surface area of ​​less than / g, water, and an admixture. The aforementioned pile-filling soil cement satisfies the following formulas (i), (ii), and (iii): The aforementioned cement is either ordinary Portland cement, low-heat Portland cement, or moderate-heat Portland cement, and the steel pipe soil cement pile 1 is one of these. 30≦C / (C+GGBFS)×100≦70…(i) 80≦W / (C+GGBFS)×100≦160…(ii) 0.1≦SP / (C+GGBFS)×100≦6 …(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). Furthermore, the steel pipe soil cement pile 1 is divided into a pile tip portion 4a and a general pile portion 3a located on the ground side of the pile tip portion 4a. The pile-peripheral filling soil cement formed in the general pile section 3a satisfies formulas (i), (ii), and (iii). The pile tip filling cement formed at the pile tip portion 4a preferably satisfies formulas (i), (iii) and formula (iv) below. 45≦W / (C+GGBFS)×100≦110…(iv) However, in equation (iv), 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). In the following explanation, "soil cement filling the general section of the pile" will be referred to as "general section soil cement," and "cement filling the pile tip" will be referred to as "tip cement."

[0014] As shown in Figure 1, the steel pipe soil cement pile 1 of this embodiment consists of a steel pipe 2 embedded in the ground and pile-circumferential filling soil cement 5 formed around the steel pipe 2. The steel pipe 2 is driven to a depth where a supporting layer exists. That is, the tip of the steel pipe 2 penetrates the supporting layer. In the following description, when the steel pipe 2 is embedded in the ground, the end on the above-ground side (upper side) of the longitudinal ends of the steel pipe 2 may be called the rear end, and the end on the underground side (lower side) may be called the tip.

[0015] The steel pipe soil cement pile 1 is divided into a pile tip section 4a and a general pile section 3a. More specifically, the area from the tip of the core material (steel material) upwards, corresponding to the diameter of the soil cement, is defined as the pile tip section 4a, and the area above that is defined as the general pile section 3a.

[0016] The pile-circumferential soil cement 5 is formed along the entire longitudinal direction of the steel pipe 2, that is, from the pile tip 4a to the general pile section 3a. The pile-circumferential soil cement 5 is divided into pile tip cement 4 and general pile section soil cement 3. The pile tip cement 4 reaches the bearing layer G1.

[0017] Furthermore, the steel pipe soil cement pile 1 of this embodiment is equipped with a pile head reinforcement 7 attached to the rear end of the steel pipe 2, and a footing 8. The footing 8 is provided to increase the bearing capacity of the steel pipe soil cement pile 1 in the ground. In addition, external protrusions 6 are attached to the outer circumference of the steel pipe 2.

[0018] As described above, the pile-surrounding soil cement 5 in this embodiment immediately after construction is composed of soil cement containing cement milk. Over time, the pile-surrounding soil cement 5 becomes composed of hardened soil cement.

[0019] The outer diameter of the steel pipe soil cement pile 1 is (outer diameter of steel pipe + 200) mm or more and (outer diameter of steel pipe + 400) mm or less, and a maximum of 2400 mm or less, more preferably 1700 mm or less. Here, the outer diameter of the steel pipe refers to the outer diameter of the steel pipe 2. It is desirable that the outer diameter of the steel pipe soil cement pile 1 be uniform in the direction of the pile axis. The soil cement 5 filling the pile perimeter, when the soil cement has hardened, transmits the external forces acting through the pile to the surrounding ground and exhibits excellent circumferential friction as the steel pipe soil cement pile 1 itself. If the outer diameter of the steel pipe soil cement pile 1 is less than (outer diameter of steel pipe + 200) mm, the bearing capacity of the steel pipe soil cement pile 1 decreases and effective performance may not be obtained. Also, if the outer diameter of the steel pipe soil cement pile 1 exceeds (outer diameter of steel pipe + 400) mm or exceeds 2400 mm, the excavation cost will increase, and an excessive amount of cement grout may be required.

[0020] Next, we will explain the cement slurry contained in soil cement.

[0021] The cement milk contained in soil cement consists of cement, blast furnace slag powder, water, and admixtures. The following describes the composition of the cement milk.

[0022] The cement is composed of either ordinary Portland cement, low-heat Portland cement, or moderate-heat Portland cement. When cement (C) is one of ordinary Portland cement, low-heat Portland cement, or moderate-heat Portland cement, and a portion of these is replaced with blast furnace slag powder, and an appropriate amount of chemical admixture is added, it is possible to achieve appropriate hardening delay effect, strength development, and fluidity (viscosity).

[0023] Blast furnace slag fine powder is obtained by rapidly cooling molten slag, which is formed simultaneously with pig iron in a blast furnace, with water to produce water-granulated slag, and then crushing the water-granulated slag. By mixing blast furnace slag fine powder with cement grout, the hardening reaction of soil cement can be suppressed, reducing the hardening rate and facilitating the installation of steel pipes. Furthermore, by replacing a portion of the cement with blast furnace slag fine powder, the amount of hexavalent chromium leaching into the ground G can be suppressed.

[0024] In this embodiment, blast furnace slag fine powder is used, with a specific surface area of ​​3000 cm². 2 / g~10000cm 2 Use a specific surface area within the range of / g. If the specific surface area falls below the lower limit, the hardening reaction of the soil cement will be significantly suppressed, reducing the hardening rate, which will lengthen the hardening time required to reach the desired hardness and may cause problems such as material segregation, so this is undesirable. Also, if the specific surface area exceeds the upper limit, the hardening of the soil cement will proceed rapidly, which will worsen the pile penetration resistance of the soil cement, so this is also undesirable.

[0025] [Contains cement milk] The cement mixture prepared on-site during construction must satisfy the following formula (i) in terms of the ratio of cement to the total amount of cement and blast furnace slag powder.

[0026] 30≦C / (C+GGBFS)×100≦70…(i)

[0027] In equation (i), C is the mass of cement (kg), and GGBFS is the mass of blast furnace slag powder (kg).

[0028] 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 25% or 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 G will increase, which is undesirable. The range of C / (C+GGBFS)×100 may be 25 or more, or more than 36 and 90 or less, or 40 or more and 80 or less, or 50 or more and 70 or less.

[0029] Water enhances the fluidity of the cement grout and also affects the hardness of the soil cement after hardening; therefore, the amount of water used in this embodiment is an important factor.

[0030] The cement grout used to form the general pile soil cement 3 must satisfy the following formula (ii) in terms of the ratio of water to the total amount of cement, blast furnace slag fine powder.

[0031] 80≦W / (C+GGBFS)×100≦160…(ii)

[0032] If W / (C+GGBFS)×100 falls below 80, that is, if the water-to-cement ratio of cement and blast furnace slag powder is less than 80%, the fluidity of the cement grout decreases, sufficient mixing with the in-situ soil does not occur, and it becomes impossible to form soil cement with a uniform composition, resulting in variations in strength, which is undesirable. On the other hand, if W / (C+GGBFS)×100 exceeds 160, that is, if the water-to-cement ratio of cement and blast furnace slag powder exceeds 160%, there is an excess of water, and the strength of the soil cement after hardening decreases significantly, preventing it from exhibiting the strength required for the on-site structure.

[0033] The cement grout used to form the cement 4 at the tip of the pile must satisfy the following formula (iv) in terms of the ratio of water to the total amount of cement, blast furnace slag powder, and cement.

[0034] 45≦W / (C+GGBFS)×100≦110…(iv)

[0035] In equation (iv), 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).

[0036] If W / (C+GGBFS)×100 is less than 45, that is, if the ratio of water to the total amount of cement and blast furnace slag powder is less than 45%, the fluidity of the cement grout decreases, sufficient mixing with the in-situ soil does not occur, and it becomes impossible to form cement with a uniform composition, resulting in variations in strength, which is undesirable. On the other hand, if W / (C+GGBFS)×100 exceeds 110, that is, if the ratio of water to the total amount of cement and blast furnace slag powder exceeds 110%, there is an excess of water, and the strength of the soil cement after hardening decreases significantly, making it impossible to achieve the strength required for the on-site structure.

[0037] 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.

[0038] In this embodiment, the mixing ratio of the admixture to the total amount of cement and blast furnace slag fine powder must satisfy the following formula (iii).

[0039] The range of W / (C+GGBFS)×100 is, 0.1≦SP / (C+GGBFS)×100≦6 …(iii)

[0040] In equation (iii), C is the mass of cement (kg), and GGBFS is the mass of blast furnace slag powder (kg).

[0041] SP / (C+GGBFS)×100 must be 0.1 or greater. 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 6, that is, if the mixing ratio of the admixture to the total amount of cement and blast furnace slag fine powder exceeds 6%, the effect of adding the admixture becomes saturated. The range of SP / (C+GGBFS)×100 may be 0.2 or more and 4 or less, 0.5 or more and 3 or less, or 1 or more and 2 or less.

[0042] The admixture is more preferably a chemical admixture containing one or more of the following: lignin sulfonate, oxycarboxylate, polycarboxylate, or silicophilic acid. By using the above chemical admixture as the admixture, the hardening of the soil cement, which is mixed with the in-situ soil and hardens, can be delayed, and construction defects such as high penetration during pile driving can be avoided.

[0043] Furthermore, the admixture may contain, in place of or together with, the above-mentioned chemical admixture, an air-entraining agent, a high-performance water-reducing agent, an air-entraining water-reducing agent, a fluidizing agent, etc.

[0044] Furthermore, the pile-surrounding soil cement 5 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 pile-surrounding soil cement can be suitably used even if the soil type of the ground is high-organic soil, sludge, or other special soils.

[0045] 1.0 m of in-situ soil when forming cement 4 at the pile tip. 3The amount of solidifying agent (cement and blast furnace slag fine powder) added to the soil is preferably between 800 kg and 1200 kg. 3 By adding 800 kg or more of a hardening agent, the cement after hardening can have the strength required for the on-site structure. 3 By limiting the amount of solidifying agent added to 1200 kg or less, good fluidity can be maintained, pile penetration ability can be preserved, and the amount of hexavalent chromium leaching into the ground G can be suppressed.

[0046] 1.0 m of in-situ soil when forming soil cement 3 for the general pile section. 3 The amount of solidifying agent added is preferably between 100 kg and 500 kg. (1.0 m of in-situ soil) 3 By adding 100 kg or more of the solidifying agent, the soil can be mixed with the in-situ soil while maintaining good fluidity, and sufficient strength for construction can be obtained after hardening. 3 By limiting the amount of solidifying agent added to 1200 kg or less, good fluidity can be maintained with the in-situ soil, pile penetration can be maintained, and the amount of hexavalent chromium leaching into the ground G can be suppressed.

[0047] In this embodiment, it is preferable to prepare the cement grout at the construction site of the steel pipe pile. Specifically, it is preferable to prepare the cement grout at the construction site by mixing cement, blast furnace slag powder, water, and pre-admixture, and then supply the prepared cement grout to the excavated hole made in the ground G.

[0048] It is preferable that the steel pipe 2 is a steel pipe with external protrusions. This effectively ensures integration with the pile-filling soil cement 5, forming a structurally stable pile foundation. In addition, the outer diameter of the steel pipe 2 is preferably in the range of 400 mm to 2000 mm, more preferably 400 mm to 1500 mm. Within this range, it can effectively integrate with the pile-filling soil cement 5 and satisfy the required performance as a pile foundation.

[0049] As shown in Figure 1, the steel pipe soil cement pile 1 is driven to a depth where the cement 4 at the pile tip reaches the supporting layer G1 of the ground G. In Figure 1, the steel pipe soil cement pile is driven to a depth where it reaches the supporting layer G1, but the cement 4 at the pile tip does not necessarily have to reach the supporting layer G1.

[0050] Although the embodiment described includes a steel pipe soil cement pile 1 having a pile tip portion 4a, a steel pipe soil cement pile 1 may also be provided without a pile tip portion 4a, consisting only of a general pile portion 3a. For example, if the steel pipe soil cement pile 1 has not reached the supporting layer G1, a steel pipe soil cement pile 1 consisting only of a general pile portion 3a may be provided.

[0051] [Construction method for steel pipe soil cement piles] [First example of construction] Next, we will describe the first construction example of the construction method for the steel pipe soil cement pile 1 described above. Figures 2 to 6 are diagrams showing the construction procedure in the first construction example of the steel pipe soil cement pile 1 of this embodiment.

[0052] As shown in Figure 2, an expanding / contracting drilling head 20 equipped with a stirring blade 21 is inserted into the steel pipe 2, and the steel pipe 2 is inserted into the ground while the ground G is excavated by the expanding / contracting drilling head 20 at the attachment position of the pipe end 22. Excavation by the expanding / contracting drilling head 20 is carried out in the pile axis direction up to the attachment position of the pile tip 4a of the steel pipe 2, for example, to a depth that reaches the supporting layer G1.

[0053] Next, as shown in Figure 3, cement grout is injected from a nozzle (not shown) provided on the expanding / contracting excavation head 20. The cement grout used satisfies equations (i), (ii), and (iii) above. Along with the injection of cement grout, the in-situ soil and cement grout are stirred by the stirring blade 21 to form the general pile soil cement 3. At the same time as the soil cement is formed, the steel pipe 2 is sunk into the general pile soil cement 3.

[0054] Next, as shown in Figure 4, when the expanding / contracting excavation head 20 reaches the vicinity of the supporting layer G1, cement grout satisfying equations (i), (iii), and (iv) above is injected to form the pile tip cement 4. The cement grout used to form the pile tip cement 4 is adjusted to satisfy equation (iv) above by reducing the water content compared to the cement grout used to form the soil cement 3 for the general part of the pile. In addition, the pile tip cement 4 is constructed without mixing with the in-situ soil to form a cement solidified body, but a portion of the pile tip cement 4 may include soil cement formed by mixing with the in-situ soil.

[0055] After forming the cement 4 at the pile tip, the expanding and contracting drilling head 20 is withdrawn, as shown in Figure 5, to form the pliers section 25.

[0056] Subsequently, as shown in Figure 6, backfill soil is placed in the pylon section 25 to form the excavation section 26, thereby completing the construction of the steel pipe soil cement pile 1.

[0057] [Second example of construction] Next, a second construction example of the steel pipe soil cement pile 1 described above will be explained. Figures 7 to 12 are diagrams showing the construction procedure in the second construction example of the steel pipe soil cement pile 1 of this embodiment.

[0058] As shown in Figure 7, the ground G at the mounting position of the pipe opening 22 is excavated using an expanding / contracting drilling head 20 equipped with a stirring blade 21. Excavation by the expanding / contracting drilling head 20 is carried out in the pile axis direction up to the mounting position of the pile tip 4a of the steel pipe 2, for example, to a depth that reaches the supporting layer G1.

[0059] Next, as shown in Figure 8, cement grout is injected from a nozzle (not shown) provided on the expanding / contracting excavation head 20. The cement grout used satisfies equations (i), (ii), and (iii) above. Along with the injection of cement grout, the in-situ soil and cement grout are mixed by the stirring blade 21 to form the general pile section soil cement 3.

[0060] Next, as shown in Figure 9, when the expanding / contracting drilling head 20 reaches the vicinity of the supporting layer G1, cement grout satisfying equations (i), (iii), and (iv) above is injected to form the pile tip cement 4. The cement grout used to form the pile tip cement 4 is adjusted to satisfy equation (iv) above by reducing the water content compared to the cement grout used to form the soil cement 3 of the general pile section.

[0061] Subsequently, as shown in Figure 10, the expanding / contracting drilling head 20 is withdrawn, and as shown in Figure 11, the steel pipe 2 is buried.

[0062] Subsequently, as shown in Figure 12, backfill soil is placed in the pylon section 25 to form the excavation section 26, thereby completing the construction of the steel pipe soil cement pile 1 according to the second construction example.

[0063] During the construction process, it is desirable that the cement grout supplied to the steel pipes 2 buried underground be prepared at the construction site of the steel pipe soil cement piles 1 by mixing cement, blast furnace slag powder, water, and admixtures. By preparing the cement grout on-site, it is possible to produce cement grout that is appropriate for the detailed soil conditions of the site, which become clear during the construction phase. This makes it possible to provide cement grout that is suitable for the site conditions, thereby reducing the risk of environmental pollution, improving strength development, and improving fluidity.

[0064] Furthermore, when preparing cement milk, blast furnace cement can be used as the cement. In this case, it is preferable to adjust the amounts of blast furnace cement and blast furnace slag powder so that the total amount of blast furnace slag contained in blast furnace slag powder and blast furnace slag contained in blast furnace cement, and the mixing ratio of cement contained in blast furnace cement, satisfies formula (v) below, instead of formula (i) above. The reason for limiting formula (v) is the same as in the case of formula (i).

[0065] 30≦C' / (C'+GGBFS')×100≦70 …(v)

[0066] In equation (v), C' is the mass of cement contained in the blast furnace cement (kg), and GGBFS' is the total amount of blast furnace slag fine powder and blast furnace slag contained in the blast furnace cement (kg).

[0067] For blast furnace cement, a type manufactured by mixing blast furnace slag fine powder with ordinary Portland cement can be used. For example, any of the following types specified in JIS R 5211:2019 can be used: Type A (amount of blast furnace slag: more than 5% but within 30%), Type B (amount of blast furnace slag: more than 30% but within 60%), or Type C (amount of blast furnace slag: more than 60% but within 70%).

[0068] In the steel pipe soil cement pile 1 of this embodiment, it is desirable that the formed soil cement exhibits the following performance characteristics due to its construction characteristics.

[0069] [Uniaxial compressive strength of soil cement at 28 days of age] The unconfined compressive strength of soil cement, measured in accordance with JIS A 1216:2020 "Unconfined Compression Test Method for Soil," is preferably 1000 kN / m for the general pile section 3a. 2 That concludes the explanation. When the value is above this level, the soil-cement section is not damaged by the shear force transmitted from the pile, and frictional force can be effectively transmitted to the surrounding ground. Furthermore, the unconfined compressive strength at the pile tip 4a is 15,000 kN / m 2 It is preferable that the strength is equal to or greater than this value. A strength equal to or greater than this value allows for excellent tip bearing capacity and effective transmission of external forces to the surrounding ground. If this strength is too low, it is not possible to form a structurally stable pile foundation. In addition, at the pile tip 4a, the hardening material (also called "hydraulic substance" or "cement hardened body") is basically used to replace the in-situ soil to form the hardened material. Therefore, in the test results exemplified in this embodiment, it is acceptable as long as the above compressive strength is achieved for sandy soil, which is the type of soil that is most likely to produce high strength.

[0070] [Resistance to pile penetration] In some cases, piles are driven into the soil cement after cement grout has been injected and mixed into the in-situ soil. If the strength of the soil cement is too high during pile penetration, there is a concern that the pile may not be driven to the desired position, thus impairing structural performance. Therefore, the penetration resistance value, measured according to "JIS A 1147: Test Method for Setting Time of Concrete," should be 8.0 kN / m after 8 hours post-placement. 2 The following is required:

[0071] [Hexavalent chromium elution value] After soil cement is 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.

[0072] Furthermore, when pumping cement grout into the ground, if the viscosity is too high, pumping becomes impossible. Therefore, the viscosity of the cement grout must be kept low. For this reason, the cement grout before being injected into the ground must have the following properties.

[0073] [P funnel flow time] The flow time through the P funnel, measured in accordance with "JSCE-F521 Method for testing the fluidity of injection mortar in pre-packed concrete (method using a P funnel)," must be kept to 14 seconds or less.

[0074] In this embodiment, the excavation and cement grout injection were performed simultaneously. However, it is also possible to perform the construction by first excavating and forming the location for burying the steel pipe soil cement pile 1, and then supplying the cement grout.

[0075] The structure and construction method of the steel pipe soil cement pile 1 described above demonstrate an effect in suppressing the leaching of hexavalent chromium, an environmentally harmful substance, thereby reducing the risk of environmental pollution. Furthermore, the penetration resistance is kept sufficiently low. This is thought to be the result of the delayed hardening of the soil cement due to the influence of blast furnace slag fine powder, and the effect of the admixture (chemical admixture). As a result, the pile penetration resistance is kept sufficiently low, providing a specification that poses no problems during construction. In addition, from the perspective of CO2 emissions, using blast furnace slag fine powder as a cement substitute keeps CO2 emissions low.

[0076] It should be noted that the technical scope of the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention.

[0077] For example, 1.0 m of in-situ soil 3 The amount of solidifying agent added per unit area may be less than 800 kg or more than 1200 kg at the pile tip 4a, and may be less than 100 kg or more than 500 kg at the general pile section 3a. The steel pipe 2 used in the steel pipe soil cement pile 1 does not necessarily have to be a steel pipe with external protrusions. [Examples]

[0078] Next, an example of a case study conducted to support the effectiveness of the steel pipe soil cement pile 1 and its construction method according to the above-described embodiment will be explained below.

[0079] At an ambient temperature of 20°C, cement grout No. 1 to No. 15 was produced by mixing cement, blast furnace slag powder, water, and admixtures in predetermined proportions, as shown in Tables 1 and 2. Note that No. 1 to No. 3 listed in Table 1 are cement grout for the pile tip, and No. 4 to No. 15 listed in Table 1 are cement grout for the general part of the pile. The blast furnace slag powder had a surface area of ​​4100 cm². 2 The product used was one with a concentration of / g. Ordinary Portland cement was used. The admixtures used were chemical admixtures with the compositions shown in Table 3 below.

[0080] Next, the cement slurry No. 1 to No. 15 was mixed with in-situ soil, specifically sandy soil (simulated soil) and clayey soil (simulated soil), to create soil cement. (1 m of in-situ soil) 3 The amount of solidifying agent added per unit area is 1000 kg / m³ at the pile tip section 4a. 3 The water-to-powder ratio (W / P) was set to 50%. In the general pile section 3a, 1 m of in-situ soil was used. 3 The amount of solidifying agent added per unit is 300 kg / m³. 3 The water-to-powder ratio (W / P) was set to 100% and 150%. The substitution rate of blast furnace slag fine powder (GGBFS) for cement (N) was set to 0 (comparative example), 50%, and 70%. Bentonite (B) was added at 20 kg / m³ only when the target soil type was sandy soil. 3 The following was added: For the admixture (SP), a chemical admixture mainly composed of oxycarboxylic acid was added at a concentration of 1.0 to 3.0 wt% of the powder components. The sandy soil was a mixture of silica sand and kaolinite clay in a mass ratio of silica sand:kaolinite clay = 9:1. The clayey soil was kaolinite clay.

[0081] [Table 1]

[0082] [Table 2]

[0083] [Table 3]

[0084] 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 flow time of the cement milk through a P funnel was also measured. These measurements were performed as described above. The results are shown in Tables 1 and 2. Note that "ND" in the needle penetration test results indicates a test value of 0.1 N / mm. 2 This indicates that it is less than [amount]. Furthermore, the needle penetration test results are from 8 hours after mixing. "Solidifying agent added amount" refers to the amount (kg) of cement (C) and blast furnace slag fine powder (GGBFS), and "Solidifying agent added amount" is calculated per 1 m³ of in-situ soil. 3 This indicates the amount of solidifying agent added relative to the total amount.

[0085] Table 1 shows the CO2 emissions during the production of each soil cement. 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 the amount added was very small and its impact on CO2 intensity was expected to be small.

[0086] CO2 emissions from cement milk (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)

[0087] As shown in Tables 1 and 2, all of Nos. 1, 2, 4, 5, 7, 8, 10, 11, 13, and 14, which are formulated with blast furnace slag fine powder, satisfy the specified performance values, indicating that cement grout suitable for both the pile tip 4a and the general pile section 3a of steel pipe soil cement piles is provided. 3 The CO2 emissions per unit area for piles No. 1 and 2, which are used for the pile tip, are 500 kg / m 3 The following applies to piles for general use: Nos. 4, 5, 7, 8, 10, 11, 13, and 14, which have a load capacity of 300 kg / m 3 The results were as follows. From this, it was found that by replacing a portion of the cement with blast furnace slag powder, it is possible to reduce CO2 emissions related to the production of cement milk, making it a material that contributes to the preservation of the global environment.

[0088] On the other hand, samples No. 3, 6, 9, 12, and 15, which did not contain blast furnace slag powder, showed slightly higher levels of hexavalent chromium leaching. 3 The CO2 emissions per unit area for No. 3, which is intended for the pile tip, are 500 kg / m 3 For piles intended for general use, Nos. 6, 9, 12, and 15, the capacity is 300 kg / m 3 These values ​​all exceeded the ranges shown in the examples where blast furnace slag powder was incorporated, and all of them showed higher values ​​than those in the examples where blast furnace slag powder was incorporated.

[0089] Based on the above results, it can be seen that the steel pipe soil cement pile 1 of the present invention exhibits excellent performance.

[0090] Furthermore, it is possible to replace the components in the above embodiments with numerical components as appropriate, without departing from the spirit of the present invention, and the above modifications may be combined as appropriate. For example, in this embodiment, sandy soil and cohesive soil are used as in-situ soil, but even when the cement milk of the present invention is used in the Kanto loam soil layer, which has a higher risk of hexavalent chromium leaching, suppression of hexavalent chromium leaching can be expected. [Explanation of symbols]

[0091] 1. Steel pipe soil cement pile 2 Steel pipe 3. General pile section: Soil cement 4. Cement at the tip of the pile 5. Soil cement filling around the pile 6 External protrusion 7. Reinforcement bars at the pile heads 20 drilling heads 21 Stirring blade 22 Mouth tube 25 Pliers 26 Drilling section G Ground G1 support layer

Claims

1. A steel pipe soil cement pile comprising a steel pipe buried in the ground and pile-circumferential filling soil cement formed around the steel pipe, The aforementioned pile-filling soil cement consists of soil cement containing cement milk. The cement milk mentioned above contains cement and 3000 cm ２ / g or more 10000cm ２ It contains a solidifying agent consisting of blast furnace slag fine powder with a specific surface area of ​​less than / g, water, and an admixture. The aforementioned pile-filling soil cement satisfies the following formulas (i), (ii), and (iii): A steel pipe soil cement pile, wherein the cement used is either ordinary Portland cement, low-heat Portland cement, or moderate-heat Portland cement. 30≦C / (C+GGBFS)×100≦70…(i) 80≦W / (C+GGBFS)×100≦160…(ii) 0.1≦SP / (C+GGBFS)×100≦6…(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. The aforementioned steel pipe soil cement pile is divided into a pile tip portion and a general pile portion located above ground level than the pile tip portion. The pile-peripheral filling soil cement formed in the general part of the pile satisfies the above formulas (i), (ii), and (iii), The pile tip filling cement formed at the pile tip satisfies formulas (i), (iii) and formula (iv) below, as described in claim 1. 45≦W / (C+GGBFS)×100≦110…(iv) However, in equation (iv), 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).

3. In the aforementioned soil cement, 1.0 m of in-situ soil ３ The amount of the solidifying agent mixed per unit area is In the general pile section, the weight is between 100 kg and 500 kg. The steel pipe soil cement pile according to claim 2, characterized in that the pile tip weighs 800 kg or more and 1200 kg or less.

4. The steel pipe soil cement pile according to claim 1 or claim 2, wherein the admixture (SP) is a chemical admixture containing a lignin sulfonate, an oxycarboxylate, a polycarboxylate, or a silicoid.

5. The steel pipe soil cement pile according to claim 1 or 2, characterized in that the steel pipe is a steel pipe with external protrusions.

6. A method for constructing steel pipe soil cement piles, in which soil cement is formed around a steel pipe buried in the ground, The aforementioned pile perimeter filling soil cement is formed by soil cement containing cement milk, The cement milk mentioned above contains cement and 3000 cm ２ / g or more 10000cm ２ It contains a solidifying agent consisting of blast furnace slag fine powder with a specific surface area of ​​less than / g, water, and an admixture. The aforementioned pile-filling soil cement satisfies the following formulas (i), (ii), and (iii): A method for constructing steel pipe soil cement piles, wherein the cement used is either ordinary Portland cement, low-heat Portland cement, or moderate-heat Portland cement. 30≦C / (C+GGBFS)×100≦70…(i) 80≦W / (C+GGBFS)×100≦160…(ii) 0.1≦SP / (C+GGBFS)×100≦6…(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).

7. The aforementioned steel pipe soil cement pile is divided into a pile tip portion and a general pile portion located above ground level than the pile tip portion. The pile-peripheral filling soil cement formed in the general part of the pile satisfies the above formulas (i), (ii), and (iii), The method for constructing a steel pipe soil cement pile according to claim 6, wherein the pile tip filling cement formed at the pile tip satisfies formulas (i), (iii) and formula (iv) below. 45≦W / (C+GGBFS)×100≦110…(iv) However, in equation (iv), 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).

8. In the above soil cement construction method, 1.0 m of in-situ soil ３ The amount of the solidifying agent mixed per unit area is At the tip of the aforementioned pile, 800 kg to 1200 kg / m ３ And, In the general section of the pile, 100 kg or less and 500 kg / m ３ The method for constructing steel pipe soil cement piles according to claim 7, characterized in that it is the same as the present invention.

9. The method for constructing steel pipe soil cement piles according to claim 6 or claim 7, wherein the admixture (SP) is a chemical admixture containing lignin sulfonate, oxycarboxylate, polycarboxylate, or silicogenic compound.

10. The method for constructing a steel pipe soil cement pile according to claim 6 or claim 7, characterized in that the steel pipe is a steel pipe with external protrusions.

11. A method for constructing a steel pipe soil cement pile according to claim 6 or claim 7, comprising: mixing the solidifying agent, the water, and the admixture to prepare the cement milk at the construction site of the steel pipe soil cement pile; and supplying the prepared cement milk around the steel pipe buried in the ground.

12. Blast furnace cement is used as the aforementioned cement. A method for constructing a steel pipe soil cement pile according to claim 11, 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 the following formula (v) instead of formula (i). 30≦C' / (C'+GGBFS')×100≦70...(v) However, in formula (v), 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.

Images