Ground improvement body, construction method thereof, design method thereof and quality management method thereof

Abstract

To provide a ground improvement body low in cost and excellent in support strength and horizontal strength, a construction method thereof, a design method thereof, and a quality management method thereof.SOLUTION: A ground improvement body 1 is provided with a column-like cement part 3 buried in the ground 2, and a concrete long core member 4 with an upper end 4a formed larger than a lower end part 4b, which is buried in the cement part 3. The upper end part 4a of the core member 4 projects upward from an upper end part 3a of the cement part 3 and the ground 2.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a ground improvement body having a core material buried in a cement part, a construction method thereof, a design method thereof, and a quality control method thereof. [Background technology]

[0002] Conventionally, a cement column method is known as a ground improvement technique in which a reinforcing columnar structure of soil cement is formed in the ground. Such reinforcing columnar structures using soil cement columns are mainly used as ground improvement techniques to improve bearing capacity. Also known are a soil cement column in which a steel pipe is arranged as a reinforcing core material (see, for example, Patent Documents 1 to 3), a tapered soil cement column in which a steel pipe is arranged as a reinforcing core material (see, for example, Patent Document 4), and a soil cement column in which a tapered concrete column is arranged as a reinforcing core material (see, for example, Patent Document 5). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2001-182055 A [Patent Document 2] JP 2007-63881 A [Patent Document 3] JP 2007-191990 A [Patent Document 4] JP 2001-98542 A [Patent Document 5] JP 2011-47273 A Summary of the Invention [Problem to be solved by the invention]

[0004] When steel pipes are used as the core material as in the inventions described in the above Patent Documents 1 to 4, the material strength, frictional force, and end bearing capacity can be increased, and a bearing capacity higher than that of the normal soil cement method can be obtained, but no consideration is given to the appropriate external shape structure of the soil cement column and the core material to reliably transmit the stress transmitted from the steel pipe to the soil cement column when a vertical load is applied. In addition, steel pipes are expensive.

[0005] In this regard, in the case of the ground improvement body of the invention described in Patent Document 5, by arranging the concrete pillars away from the bottom end of the soil cement column and above, it is possible to improve the bearing capacity by the bearing capacity of the soil cement column and the frictional force of the concrete pillars, but the horizontal force of the building supported by the ground improvement body is not taken into consideration. Also, the bearing capacity in the case of the invention described in Patent Document 5 is determined by the ground destruction around and at the tip of the soil cement column, and the concept of the bearing capacity mechanism is no different from conventional methods.

[0006] The present invention has been made in consideration of the above points, and aims to provide a ground improvement body that is inexpensive and has excellent bearing capacity and horizontal force, a construction method thereof, a design method thereof, and a quality control method thereof. [Means for solving the problem]

[0007] The ground improvement body described in claim 1 comprises a columnar cement section buried in the ground, and a long core material made of concrete whose upper end is larger in diameter than its lower end and is embedded in the cement section, the core material being tapered in diameter gradually expanding from its lower end to its upper end, and whose upper end protrudes upward relative to the upper end of the cement section and the ground.

[0008] The ground improvement body according to claim 2 is the ground improvement body according to claim 1, wherein the lower end of the core material is positioned above and away from the lower end of the cement portion.

[0009] The ground improvement body according to claim 3 is the ground improvement body according to claim 1, further comprising a pile cap into which the upper end of the cement portion and the upper end of the core material protruding upward relative to the ground are embedded.

[0010] The construction method of a ground improvement body described in claim 4 is a construction method of a ground improvement body comprising a columnar cement section and a long core material made of concrete having one end formed with a larger diameter than the other end, in which a borehole is drilled in the ground while a cement-based solidification material is injected to mix and stir with soil to produce soil cement, and before the soil cement hardens, the core material is inserted into the soil cement with the other end facing downward and one end protruding upward from the ground, and the soil cement is hardened to form the cement section.

[0011] The construction method of a ground improvement body as described in claim 5 is the construction method of a ground improvement body as described in claim 4, in which when inserting a core material into the soil cement, the other end of the core material is inserted upwardly away from the lower end of the soil cement.

[0012] The construction method of a ground improvement body described in claim 6 is a construction method of a ground improvement body in which a ground improvement body comprising a columnar cement section and a long core material made of concrete having one end formed with a larger diameter than the other end is constructed on the ground, in which cement milk is injected into an excavation hole formed in the ground, and before the cement milk hardens, the core material is inserted into the cement milk with the other end facing downward and the one end protruding upward from the ground, and the cement milk is allowed to harden to form the cement section.

[0013] The construction method of a ground improvement body as described in claim 7 is the construction method of a ground improvement body as described in claim 6, in which when inserting a core material into cement milk, the other end of the core material is inserted so as to be separated upward from the lower end of the cement milk.

[0014] The construction method of a ground improvement body according to claim 8 is the construction method of a ground improvement body according to claim 4 or 6, in which a plurality of ground improvement bodies are arranged side by side and constructed on the ground.

[0015] The design method of a ground improvement body described in claim 9 is a design method of a ground improvement body constructed by the construction method of a ground improvement body described in claim 4 or 6, and designs the bearing capacity of the ground improvement body based on the splitting tensile strength of the cement part of the ground improvement body.

[0016] The quality control method for ground improvement bodies described in claim 10 is a quality control method for ground improvement bodies that manages the quality of ground improvement bodies constructed by the construction method for ground improvement bodies described in claim 4 or 5, and determines whether or not the bearing capacity satisfies a specified design value by calculating the splitting tensile strength of the cement part of the ground improvement body from soil cement collected during construction.

[0017] The quality control method for ground improvement bodies described in claim 11 is a quality control method for ground improvement bodies that manages the quality of ground improvement bodies constructed by the construction method for ground improvement bodies described in claim 6 or 7, and determines whether or not the bearing capacity satisfies a specified design value by calculating the splitting tensile strength of the cement part of the ground improvement body from cement milk collected during construction. Effect of the Invention

[0018] According to the present invention, it is possible to provide a ground improvement body which is inexpensive and has excellent bearing capacity and horizontal force. [Brief description of the drawings]

[0019] [Figure 1] This is a cross-sectional view showing a ground improvement body of one embodiment of the present invention, where (a) shows an example in which the lower end of the core material is in contact with the lower end of the borehole, and (b) shows an example in which the lower end of the core material is separated upward from the lower end of the borehole. [Diagram 2] 1A to 1D are perspective views showing an example of construction of the same ground improvement body. [Diagram 3]1A to 1E are explanatory cross-sectional views showing an example of a construction method for the same ground improvement body. [Figure 4] 11A to 11E are explanatory cross-sectional views showing other examples of the construction method of the same ground improvement body. [Diagram 5] 11A to 11E are explanatory cross-sectional views showing still another example of the construction method of the same ground improvement body. [Figure 6] This is a cross-sectional view showing an example of a core material used in a push-out load test to demonstrate the validity of the support capacity calculation formula. [Figure 7] 1A is a cross-sectional view showing an example of a test specimen used in the above-mentioned punching load test, which has an excess reinforcement portion below the core material, and FIG. 1B is a cross-sectional view showing an example of a test specimen used in the above-mentioned punching load test, which does not have an excess reinforcement portion below the core material. [Figure 8] This is a graph showing a comparison between the bearing capacity calculated using the bearing capacity calculation formula and the actual measured punching strength obtained by the same punching load test. [Figure 9] 1 is a graph showing the relationship between load and displacement in a plate loading test. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0021] 1(a) and 1(b), reference numeral 1 denotes a ground improvement body. The ground improvement body 1 integrally comprises a long columnar cement portion 3 buried in ground 2 and a long core material 4 buried in the cement portion 3.

[0022] The cement portion 3 is also called a cement column or the like. The cement portion 3 is formed from soil cement or cement milk. The cement portion 3 is formed into a cylindrical shape of a predetermined length. The cement portion 3 has a basically constant diameter dimension from the upper end portion 3a to the lower end portion 3b. The cement portion 3 is entirely buried in the ground 2, and the upper end portion 3a is positioned approximately flush with the ground. The cement portion 3 basically extends along a vertical direction.

[0023] The core material 4 is a cylindrical or cylindrical concrete column. In this embodiment, the core material 4 is a hollow cylindrical concrete column, in which PC steel wires (reinforcing bars) are embedded as reinforcing members. As an example, a discarded utility pole or the like is used for the core material 4. The length of the core material 4 is set to be equal or approximately equal to the length of the cement portion 3, for example.

[0024] The core material 4 is formed so that the upper end 4a has a larger diameter than the lower end 4b. In this embodiment, the core material 4 is formed in a tapered shape that gradually expands in diameter from the lower end 4b to the upper end 4a. The core material 4 is disposed coaxially with the cement portion 3.

[0025] The lower end 4b (below the pile) of the core material 4 may be in contact with the lower end 3b of the cement section 3 (Fig. 1(a)), or may be located above and away from the lower end 4b of the core material 4 with an excess portion 3c of the cement section 3 formed below the lower end 4b of the core material 4 as a vertical load transmission range for transmitting the vertical load from the core material 4 to the cement section 3 (Fig. 1(b)). In this case, the distance between the lower end 4b of the core material 4 and the lower end 3b of the cement section 3 is set to be, for example, equal to or greater than the maximum diameter dimension of the core material 4.

[0026] Additionally, the upper end 4a (pile head) of the core material 4 protrudes upward relative to the upper end 3a of the cement part 3 and the ground 2. The upper end 4a of the core material 4, together with the upper end of the cement part 3, is embedded in, for example, a pile cap 5. The pile cap 5 is a concrete mass that supports the superstructure of a building or the like and transmits the load to the ground improvement body 1 via the core material 4. The upper part of the pile cap 5 that supports the superstructure is planar (flat).

[0027] Preferably, a plurality of ground improvement bodies 1 are set on the ground 2. For example, as shown in FIG. 2(a), a single ground improvement body is arranged like a pile, as shown in FIG. 2(b), a plurality of rows of ground improvement bodies are arranged in a wall shape, as shown in FIG. 2(b), a plurality of ground improvement bodies are arranged in a lattice shape, as shown in FIG. 2(c), and a plurality of ground improvement bodies are arranged in a block shape, as shown in FIG. 2(d). The pile cap 5 is commonly arranged over a plurality of ground improvement bodies 1, for example, over all the ground improvement bodies 1, and is large enough to cover the entire plurality of ground improvement bodies 1 when viewed from above. In this way, the support structure is composed of the plurality of ground improvement bodies 1 and the pile cap 5 arranged over their core material 4.

[0028] Next, a construction method for the soil improvement body 1 according to one embodiment will be described.

[0029] The construction method of the ground improvement body 1 can be broadly divided into (A) a construction method in which the cement part 3 is a soil cement column, and (B) a construction method in which the cement part 3 is a cement milk column.

[0030] Regarding (A) above, first, as shown in FIG. 3(a), an excavator 10 is placed at the excavation position of the ground 2, and as shown in FIG. 3(b), a cement-based solidification material (soil cement) is injected into the excavation hole 11 while performing preliminary excavation by the excavator 10, and as shown in FIG. 3(c), the cement-based solidification material is mixed and stirred with the local soil to form soil cement 12, and the excavation is performed to the target depth. When the excavation hole 11 reaches the target depth, the excavator 10 is pulled out of the excavation hole 11 while stirring again, and the soil cement 12 is hardened. Before the soil cement 12 hardens, as shown in FIG. 3(d), the core material 4 is inserted into the soil cement 12 with the small diameter side facing downward so that it is separated upward from the lower end of the soil cement 12 and the large diameter side protrudes upward from the ground 2 so that the pile cap 5 (FIGS. 1(a) and 1(b)) can be attached. Then, the soil cement 12 is hardened to form the cement portion 3 as shown in Fig. 3(e) In this case, for example, a drum-type agitator is used as the excavation head of the excavator 10.

[0031] Regarding (B) above, for example, the following two different construction methods are possible.

[0032] For example, first, as shown in FIG. 4(a), a drilling machine 10 is placed at a drilling position of the ground 2, and as shown in FIG. 4(b), preliminary drilling is performed by the drilling machine 10 to form a drilling hole 11 to a target depth. Next, as shown in FIG. 4(c), cement milk 13 is injected into the drilling hole 11, and as shown in FIG. 4(d), before the cement milk 13 hardens, the core material 4 is inserted into the cement milk 13 with the small diameter side facing downward, away from the lower end of the cement milk 13, and the large diameter side protrudes upward from the ground 2 so that the pile cap 5 (FIGS. 1(a) and 1(b)) can be attached. Then, the cement milk 13 is hardened to form a cement part 3 as shown in FIG. 4(e). In this case, for example, a screw is used as the drilling head of the drilling machine 10.

[0033] As another method, for example, as shown in FIG. 5(a), a drilling machine 10 is placed at a drilling position of the ground 2, and as shown in FIG. 5(b), preliminary drilling is performed by the drilling machine 10 to form a drilling hole 11 to a target depth. Next, as shown in FIG. 5(c), cement milk 13 is injected into the drilling hole 11 while the drilling machine 10 is repeatedly moved up and down in the drilling hole 11, and as shown in FIG. 5(d), before the cement milk 13 hardens, the core material 4 is inserted into the cement milk 13 with the small diameter side on the bottom so that it is separated upward from the lower end of the cement milk 13 and the large diameter side protrudes upward from the ground 2 so that the pile cap 5 (FIGS. 1(a) and 1(b)) can be attached. Then, the cement milk 13 is hardened to form a cement part 3 as shown in FIG. 5(e). In this case, for example, a drum-type mixing device is used as the drilling head of the drilling machine 10.

[0034] The bearing mechanism of the ground improvement body 1 of this embodiment constructed in this manner will be described below.

[0035] In the ground improvement body 1, due to a vertical load acting on the upper end 4a of the core material 4, a lateral expansion pressure P is generated in the tapered portion of the core material 4 as a wedge effect (hereinafter referred to as the taper effect), and the resistance to this pressure corresponds to the bearing force.

[0036] This lateral expansion pressure P does not depend on the ground strength around the cement portion 3 of the ground improvement body 1.

[0037] The cement part 3 on the periphery of the core material 4 undergoes splitting failure due to the taper effect. Therefore, the bearing capacity Rf of the ground improvement body 1 can be designed using the following bearing capacity calculation formula (1) based on the splitting tensile strength of the cement part 3.

[0038] R f =β σ y π(D c -d ave )·L / 4 / 1000···(1)

[0039] Here, R f is the bearing capacity [kN], β is the correction coefficient (0.75~1.00), σ y is the splitting tensile strength [N / mm 2 〕, D c is the diameter of the cement part 3 [mm], d ave is the average diameter of the core material 4 [mm], and L is the length of the cement part 3 [mm]. Note that the average diameter d ave is the maximum diameter of the core material 4, which is the diameter of the upper end portion 4a (terminal end) in this embodiment, D0 [mm], and the minimum diameter of the core material 4, which is the diameter of the lower end portion 4b (base end) in this embodiment, D [mm], ave =(D0+D) / 2.

[0040] In this embodiment, preferably, the diameter D of the cement portion 3 c The diameter D0 of the core material 4 is set to 2 to 3.5 times the maximum diameter D0 of the core material 4. For example, when the maximum diameter D0 of the core material 4 is 200 mm, the diameter D c When the maximum diameter D0 of the core material 4 is 450 mm, the diameter D cThe length L of the cement portion 3 is, for example, 15 m, and the maximum length of the core material 4 is also set to the same 15 m as the length L of the cement portion 3.

[0041] Thus, according to one embodiment, the ground improvement body 1 is constructed by embedding a long concrete core material 4, the upper end 4a of which is formed with a larger diameter than the lower end 4b, in the cement part 3 to be buried in the ground 2, so that the vertical load acting on the core material 4 generates a lateral expansion pressure P from the core material 4 to the cement part 3, and the resistance to this pressure can be generated as a support force. In addition, by positioning the lower end 4b of the core material 4 away from the lower end 3b of the cement part 3 and forming a surplus part 3c of the cement part 3 below the lower end 4b of the core material 4, even after the cement part 3 is fractured by the lateral expansion pressure P (taper effect), an axial force remains in this surplus part 3c, so that brittle fracture does not occur as when the ground 2 is fractured. In addition, even if the cement part 3 is fractured by the lateral expansion pressure P (taper effect), the cement part 3 itself is supported by the surrounding ground, so brittle fracture does not occur as when the ground 2 is fractured.

[0042] Furthermore, by leaving the upper end 4a of the core material 4 above the ground 2, a pile cap 5 can be embedded in the upper end 4a of the core material 4, thereby ensuring the horizontal force of the superstructure.

[0043] Therefore, it is possible to provide a ground improvement body 1 which is inexpensive compared to a case where, for example, a steel pipe is used as the core material, and which has excellent bearing capacity and horizontal force.

[0044] Furthermore, since the core material 4 has a tapered shape in which the diameter gradually increases from the lower end 4b to the upper end 4a, the lateral expansion pressure P can be effectively generated and, for example, an abandoned utility pole or the like can be effectively used as the core material 4.

[0045] Furthermore, regardless of the strength of the ground 2 around and below the cement section 3, even if the ground 2 is extremely soft, the bearing capacity can be calculated using the above bearing capacity calculation formula (1) by utilizing the splitting tensile strength of the cement section 3 and the geometric dimensions of the cement section 3 and the core material 4.

[0046] Furthermore, when the core material 4 is inserted into the soil cement 12 or cement milk 13, the volume expansion due to the pressure at the time of insertion also contributes to an increase in the taper effect, thereby improving the bearing capacity of the ground improvement body 1.

[0047] Furthermore, by constructing multiple ground improvement bodies 1 in a line on the ground 2, such as by constructing the ground improvement body 1 in the form of a single pile as shown in Figure 2(a), a wall as shown in Figure 2(b), a lattice as shown in Figure 2(c), or a block as shown in Figure 2(d), the ground improvement body 1 can also be used as a liquefaction countermeasure, an earth retaining wall, and an earth pressure resistant structure.

[0048] In addition, since the bearing capacity of the ground improvement body 1 can be designed based on the fracture tensile strength of the cement part 3 using the above-mentioned bearing capacity calculation formula (1), it becomes possible to freely design according to the ground pressure of the superstructure based on the strength and geometric dimensions of the cement part 3 regardless of the hardness of the ground 2.

[0049] The splitting tensile strength of the cement part 3 can be calculated from laboratory experiments using on-site soil samples. Therefore, the bearing capacity of the ground improvement body 1 can be easily designed using the above-mentioned bearing capacity calculation formula (1) without a large-scale ground survey, making it possible to design at low cost.

[0050] In addition, by calculating the splitting tensile strength of the cement section 3 using the soil cement 12 or cement milk 13 collected during construction, it is possible to use the above-mentioned bearing capacity calculation formula (1) to confirm whether the bearing capacity of the ground improvement body 1 satisfies the design value. This makes it easy to conduct a complete survey of the ground improvement body 1 using this construction method without conducting a load test, enabling high-quality quality control at low cost.

[0051] Next, a simulation test showing the validity of the above-mentioned bearing capacity calculation formula (1) will be described with reference to Figs.

[0052] As shown in FIG. 6, the tapered pile (taper angle 0.42°) has a total length of 540 mm, a diameter (D0) of the upper end 4a of 70 mm, and a diameter (D) of the lower end 4b of 63 mm, i.e., an average diameter dave A tapered pile with a diameter of 66.5 (= (70 + 63) / 2) mm was used as the core material 4, and as shown in Figures 7(a) and 7(b), the core material 4 was inserted into each cement part 3 and embedded in the test specimens. For test conditions No. 1 to No. 14, the values ​​calculated from the bearing capacity calculation formula (1) using the splitting tensile strength of the cement part 3 were compared with the actual measured values ​​of the punching resistance.

[0053] The specimens had a core material 4 made of steel, for example SS400, and the cement part 3 was formed by placing a void pipe 16 on a bottom plate 15 and filling the inside of the void pipe with soil cement or cement milk as a solidification material. Kasaoka clay mixed with silica sand No. 6 was used as the soil cement. The amount of solidification material added, C, was 300 kg / m 3 The water-cement ratio (W / C) of each was 80%. The bottom plate 15 was made of steel, for example SS400, and an opening 15a was formed in the center opposite the lower end of the core material 4 so that the bottom plate 15 would not resist the core material 4 being pressed in. The diameter of the opening 15a was, for example, φ130 mm. The void pipes 16 used had a height of 500 mm and a thickness of 4 mm. In other words, the length (L) of the cement portion 3 was 500 mm. Furthermore, the inner diameter of the void pipe 16, i.e., the diameter (D c ) as shown in Table 1, those of 150 to 250 mm were used.

[0054] [Table 1]

[0055] In addition, to test the effect of the reinforcement 3c below the lower end 4b of the core material 4 relative to the lower end 3b of the cement part 3 on the bearing capacity calculation formula (1), a test specimen with the reinforcement 3c (Fig. 7(a)) and a test specimen without the reinforcement (Fig. 7(b)) were used. The length of the reinforcement 3c was set to 70 mm.

[0056] And, for the above test conditions No. 1 to No. 14, the splitting tensile strength σ yThe bearing capacity calculated based on the bearing capacity calculation formula (1) with the correction coefficient β = 0.75 was compared with the actual punching strength measured by applying a punching load Pi to the upper end portion 4a of the core material 4. The results are shown in Figure 8.

[0057] As shown in Figure 8, the calculated values ​​are generally close to the measured values, and it can be seen that the calculated values ​​are particularly close to the measured values ​​when soil cement is used as the solidification material. This demonstrates the validity of the bearing capacity calculation formula (1) above. Regarding the presence or absence of the reinforcement, although the punching resistance was greater with the reinforcement 3c, the effect of this on the bearing capacity calculation formula (1) was not clearly shown.

[0058] Next, a test showing the difference in bearing capacity between the presence and absence of the core material 4 in the ground improvement body 1 will be described.

[0059] First, a borehole was excavated in the ground, soil cement was injected, and the borehole was excavated to the target depth while mixing with the local soil, and a concrete pole (tapered pile) was sunk as the core material 4 into the unsolidified soil cement. The core material 4 was a tapered pile (taper angle 1 / 75°) with a total length of 8 m, a diameter (D0) of the upper end 4a of 190 mm, a diameter (D) of the lower end 4b of 297 mm, and a bending crack resistance of 5 kN. c ) was 800 mm, and the excavation length of the borehole, i.e., the length of the cement part 3 (L), was 8 m. The soil cement was sampled from the site and the strength of the cement part 3 was confirmed. y ) is 0.107N / mm 2 In addition, when the correction coefficient β is set to 0.75, the bearing capacity (R f ) was 281kN.

[0060] First, it was confirmed that the core material 4 could be fixed without any problem to the cement portion 3 where the soil cement had solidified.

[0061] Next, a plate loading test was carried out on the cement part 3, where the soil cement had solidified, using heavy machinery at the age of 28 days, to measure the load and displacement and to confirm the load relative to the bearing capacity calculated by the above-mentioned bearing capacity calculation formula (1). Test conditions No. 15 to No. 17 carried out in the test are shown in Table 2.

[0062] [Table 2]

[0063] As shown in Figure 9, for test conditions No. 15 and No. 16 using core material 4, the bearing capacity R calculated by the above-mentioned bearing capacity calculation formula (1) for each load was f There is almost no displacement until the load reaches the bearing capacity R f The cement part 3 fractured when the load exceeded 281 kN (approximately 310-315 kN). However, the load decreased slowly after reaching that load. This is thought to be because even if the cement part 3 fractured, the axial force remained in the remaining cement part 3 and the excess reinforcement part 3c below the core material 4, and the cement part 3 itself was supported by the surrounding ground, so brittle fracture did not occur.

[0064] In contrast, in test condition No. 17, which did not use core material 4, the specimen yielded at a load of approximately 140 kN.

[0065] As a result, it was shown that the bearing capacity of the ground improvement body 1 is significantly increased by embedding the core material 4 in the cement part 3 with the excess reinforcement part 3c. [Explanation of symbols]

[0066] 1. Ground improvement body 2 Ground 3. Cement Section 3a Upper end 3b Bottom end 4 Core material 4a Upper end 4b Bottom end 5. Pile Cap 11 Borehole 12 Soil Cement 13 Cement Milk

Claims

1. A columnar cement portion buried in the ground; a long concrete core material having an upper end portion with a larger diameter than a lower end portion and embedded in the cement portion; The core material is tapered so that the diameter gradually increases from the lower end to the upper end, and the upper end protrudes upward relative to the upper end of the cement portion and the ground. A ground improvement body characterized by the above.

2. The lower end of the core material is located above and away from the lower end of the cement portion.

2. The ground improvement body according to claim 1 .

3. The pile cap is provided with an upper end of the cement section and an upper end of the core material protruding upward from the ground, into which is embedded 2. The ground improvement body according to claim 1 .

4. A method for constructing a ground improvement body on the ground, the method comprising: constructing a ground improvement body having a columnar cement portion and a long concrete core material having one end formed with a larger diameter than the other end; A borehole is excavated in the ground while a cement-based solidification material is injected and mixed with the soil to produce soil cement; Before the soil cement hardens, the core material is inserted into the soil cement so that the other end is on the lower side and the one end protrudes upward from the ground, The soil cement is hardened to form the cement portion. A construction method for ground improvement body comprising the steps of:

5. When inserting the core material into the soil cement, the other end of the core material is inserted upwardly away from the lower end of the soil cement. A method for constructing a ground improvement body according to claim 4.

6. A method for constructing a ground improvement body on the ground, the method comprising: constructing a ground improvement body having a columnar cement portion and a long concrete core material having one end formed with a larger diameter than the other end; Injecting cement milk into a borehole formed in the ground; Before the cement milk hardens, the core material is inserted into the cement milk so that the other end is downward and the one end protrudes upward from the ground, The cement milk is hardened to form the cement part. A construction method for ground improvement body comprising the steps of:

7. When inserting the core material into the cement milk, the other end of the core material is inserted upwardly away from the lower end of the cement milk. A method for constructing a ground improvement body according to claim 6.

8. Multiple ground improvement bodies are lined up and constructed on the ground. A method for constructing a ground improvement body according to claim 4 or 6.

9. A method for designing a ground improvement body constructed by the construction method of the ground improvement body according to claim 4 or 6, The bearing capacity of the ground improvement body is designed based on the splitting tensile strength of the cement part of the ground improvement body. A method for designing a ground improvement body comprising the steps of:

10. A quality control method for a ground improvement body constructed by the construction method of the ground improvement body according to claim 4 or 5, By calculating the splitting tensile strength of the cement part of the ground improvement body from the soil cement sampled during construction, it is judged whether the bearing capacity satisfies the specified design value. A quality control method for ground improvement bodies, comprising:

11. A quality control method for a ground improvement body constructed by the construction method of the ground improvement body according to claim 6 or 7, By calculating the splitting tensile strength of the cement part of the ground improvement body from the cement milk sampled during construction, it is judged whether the bearing capacity satisfies the specified design value. A quality control method for ground improvement bodies, comprising:

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