Ground improvement bodies, their construction methods, their design methods, and their quality control methods

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 in which a core material is embedded in the cement portion, a method for constructing the same, a method for designing the same, and a method for quality control the same. [Background technology]

[0002] Conventionally, a known ground improvement technique is the cement column method, which involves forming a reinforcing columnar structure of soil cement in the ground. Such reinforcing columnar structures using soil cement columns are mainly used for ground improvement to improve bearing capacity. In addition, there are known types in which steel pipes are placed as reinforcing core materials inside soil cement columns (see, for example, Patent Documents 1 to 3), in which steel pipes are placed as reinforcing core materials inside tapered soil cement columns (see, for example, Patent Document 4), or in which tapered concrete columns are placed as reinforcing core materials inside soil cement columns (see, for example, Patent Document 5). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2001-182055 [Patent Document 2] Japanese Patent Publication No. 2007-63881 [Patent Document 3] Japanese Patent Publication No. 2007-191990 [Patent Document 4] Japanese Patent Publication No. 2001-98542 [Patent Document 5] Japanese Patent Publication No. 2011-47273 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] As described in the inventions in Patent Documents 1 to 4 above, when steel pipes are used as the core material, the material strength, frictional force, and tip bearing capacity can be greatly utilized, and a higher bearing capacity than the conventional soil-cement method can be obtained. However, the appropriate external shape structure of the soil-cement column and the core material to reliably transmit the stress transmitted from the steel pipe into the soil-cement column when a vertical load is applied has not been considered. 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, although it is possible to improve the bearing capacity by positioning the concrete column body upward away from the lower end of the soil cement column body through the bearing capacity of the soil cement column body and the frictional force of the concrete column body, the horizontal force of the building supported by the ground improvement body body is not taken into consideration. Furthermore, in the case of the invention described in Patent Document 5, the bearing capacity is determined by the ground failure around and at the tip of the soil cement column body, and the concept of the bearing capacity mechanism is no different from before.

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

[0007] The ground improvement body according to claim 1 comprises a columnar cement portion embedded in the ground, and a long concrete core material embedded in the cement portion, the core material being tapered, with the diameter gradually increasing from the lower end to the upper end, and the upper end protruding upward from the upper end of the cement portion and the ground. The structure further comprises a pile cap into which the upper end of the cement portion and the upper end of the core material protruding upward from the ground are embedded. It is.

[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 located above and away from the lower end of the cement portion.

[0009] request request 3The described ground improvement body construction method includes a columnar cement part, a long core material made of concrete with one end formed to have a larger diameter than the other end, A pile cap into which one end of this core material is embedded, and is a ground improvement body construction method for constructing a ground improvement body provided with A pile cap into which one end of this core material is embedded, in the ground. While excavating an excavation hole in the ground, a cement-based solidifying material is injected and mixed and stirred with soil to generate soil cement. Before the soil cement hardens, the core material is inserted into the soil cement with the other end facing downward and the one end protruding upward from the ground, and the soil cement is hardened to form the cement part Then, the pile cap is attached so as to embed the upper end of the cement portion and the end of the core material that protrudes upward relative to the ground. as described.

[0010] Claim 4 The described ground improvement body construction method is, in the ground improvement body construction method described in Claim 3 wherein when inserting the core material into the soil cement, the other end of the core material is inserted so as to be separated upward from the lower end of the soil cement.

[0011] Claim 5 The described ground improvement body construction method includes a columnar cement part, a long core material made of concrete with one end formed to have a larger diameter than the other end, A pile cap into which one end of this core material is embedded, and is a ground improvement body construction method for constructing a ground improvement body provided with A pile cap into which one end of this core material is embedded, in the ground. Cement milk is injected into the excavation hole formed in the ground. 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 hardened to form the cement part Then, attach a pile cap so as to embed the upper end of the cement portion and the end of the core material that protrudes upward relative to the ground. as described.

[0012] Claim 6 The described ground improvement body construction method is, in the ground improvement body construction method described in Claim 5 wherein when inserting the core material into the 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.

[0013] Claim 7 The described ground improvement body construction method is, in Claim 3 or 5The construction method for the ground improvement body described involves constructing multiple ground improvement bodies side by side on the ground.

[0014] Claim 8 The design method for the ground improvement body described is as stated in the claim. 3 or 5 A method for designing a ground improvement body to be constructed by the construction method of the ground improvement body described herein, wherein the bearing capacity of the ground improvement body is designed based on the splitting tensile strength of the cement portion of the ground improvement body.

[0015] Claim 9 The quality control method for the ground improvement body described is as stated in the claim. 3 or 4 A quality control method for ground improvement bodies constructed by the construction method described herein, which determines whether the bearing capacity satisfies a predetermined design value by calculating the splitting tensile strength of the cement portion of the ground improvement body from the soil cement sampled during construction.

[0016] Claim 10 The quality control method for the ground improvement body described is as stated in the claim. 5 or 6 A method for controlling the quality of a ground improvement body constructed by the construction method described herein, wherein the method involves determining whether the bearing capacity satisfies a predetermined design value by calculating the splitting tensile strength of the cement portion of the ground improvement body from the cement grout sampled during construction. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a ground improvement body that is inexpensive and has excellent bearing capacity and horizontal force resistance. [Brief explanation of the drawing]

[0018] [Figure 1] This is a cross-sectional view showing a ground improvement body according to 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 excavation hole, and (b) shows an example in which the lower end of the core material is separated upward from the lower end of the excavation hole. [Figure 2] Figures (a) to (d) show perspective views of the construction examples of the above-mentioned ground improvement body. [Figure 3] Figures (a) to (e) are explanatory cross-sectional views illustrating an example of the construction method for the above-mentioned ground improvement body. [Figure 4] Figures (a) through (e) show explanatory cross-sectional views illustrating other examples of the construction method for the same ground improvement body. [Figure 5] Figures (a) through (e) show further explanatory cross-sectional views illustrating 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 loading test to demonstrate the validity of the bearing capacity calculation formula. [Figure 7] (a) is a cross-sectional view showing an example of a test specimen used in the same punch-out loading test that has an excess reinforcement below the core material, and (b) is a cross-sectional view showing an example of a test specimen used in the same punch-out loading test that does not have an excess reinforcement below the core material. [Figure 8] This graph compares the calculated bearing capacity using the bearing capacity calculation formula with the measured value of the piercing load test using the same formula. [Figure 9] This graph shows the relationship between load and displacement in a plate load test. [Modes for carrying out the invention]

[0019] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

[0020] In Figures 1(a) and 1(b), 1 is a ground improvement body. The ground improvement body 1 integrally comprises a long columnar cement section 3 embedded in the ground 2 and a long core material 4 embedded in the cement section 3.

[0021] The cement section 3 is also called a cement column, etc. The cement section 3 is formed from soil cement or cement grout. The cement section 3 is formed in a cylindrical shape of a predetermined length. The cement section 3 has a basically constant diameter from the upper end 3a to the lower end 3b. The entire cement section 3 is embedded in the ground 2, and the upper end 3a is positioned approximately flush with the ground. The cement section 3 basically extends along a vertical direction.

[0022] The core material 4 is a cylindrical or cylindrical concrete column. In this embodiment, the core material 4 is a cylindrical hollow concrete column with PC steel wire (reinforcement) embedded as a reinforcing member. As an example, discarded utility poles or the like can be used as the core material 4. The length of the core material 4 is set to be equal to or approximately equal to the length of the cement section 3, for example.

[0023] The core material 4 is formed with an upper end 4a having a larger diameter than the lower end 4b. In this embodiment, the core material 4 is formed in a tapered shape, gradually increasing in diameter from the lower end 4b to the upper end 4a. The core material 4 is arranged coaxially with the cement portion 3.

[0024] The lower end 4b (below the pile) of the core material 4 may be in contact with the lower end 3b of the cement portion 3 (Figure 1(a)), or it may be located above and separated, with an excess portion 3c of the cement portion 3 below the lower end 4b of the core material 4 serving as a vertical load transmission range for transmitting the vertical load from the core material 4 to the cement portion 3 (Figure 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 portion 3 shall be, for example, greater than or equal to the maximum diameter of the core material 4.

[0025] Furthermore, the upper end 4a (pile head) of the core material 4 protrudes upward relative to the upper end 3a of the cement portion 3 and the ground 2. The upper end 4a of the core material 4, together with the upper end of the cement portion 3, is embedded in, for example, a pile cap 5. The pile cap 5 is a concrete block 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).

[0026] Preferably, multiple ground improvement bodies 1 are set in the ground 2. For example, as shown in Figure 2(a), there is an example of arranging them as individual ground improvement bodies in a pile-like manner; as shown in Figure 2(b), there is an example of arranging multiple rows of ground improvement bodies in a wall-like manner; as shown in Figure 2(c), there is an example of arranging multiple ground improvement bodies 1 in a grid pattern; and as shown in Figure 2(d), there is an example of arranging multiple ground improvement bodies 1 in a block-like manner. The pile cap 5 is placed in common across multiple ground improvement bodies 1, for example, all of the ground improvement bodies 1, and is large enough to cover the entire set of ground improvement bodies 1 when viewed from above. In this way, the support structure is formed by multiple ground improvement bodies 1 and pile caps 5 placed across their core material 4.

[0027] Next, a construction method for the ground improvement body 1 according to one embodiment will be described.

[0028] The construction methods for the ground improvement body 1 can be broadly classified into two types: (A) a construction method when the cement section 3 is a soil cement column, and (B) a construction method when the cement section 3 is a cement milk column.

[0029] Regarding (A) above, first, as shown in Figure 3(a), the excavator 10 is positioned at the excavation site in the ground 2, and as shown in Figure 3(b), the excavator 10 is used to perform preliminary excavation while injecting a cement-based solidifying agent (soil cement) into the excavation hole 11, and as shown in Figure 3(c), the cement-based solidifying agent is mixed and stirred with the local soil to form soil cement 12, and the excavation is continued to the target depth. When the excavation hole 11 reaches the target depth, the excavator 10 is withdrawn from the excavation hole 11 while being stirred again, and the soil cement 12 is allowed to harden. Before the soil cement 12 hardens, as shown in Figure 3(d), the core material 4 is inserted into the soil cement 12 with the smaller diameter side facing downwards, away from the lower end of the soil cement 12, and with the larger diameter side protruding upwards from the ground 2 so that the pile cap 5 (Figures 1(a) and 1(b)) can be attached. Then, the soil cement 12 is hardened to form the cement section 3 as shown in Figure 3(e). In this case, for example, a drum-type agitator is used as the drilling head of the excavator 10.

[0030] Regarding (B) above, for example, the following two further different construction methods are possible.

[0031] For example, first, as shown in Figure 4(a), the excavator 10 is positioned at the excavation site in the ground 2, and as shown in Figure 4(b), preliminary excavation is performed with the excavator 10 to form a borehole 11 to the target depth. Next, as shown in Figure 4(c), cement grout 13 is injected into the borehole 11, and as shown in Figure 4(d), before the cement grout 13 hardens, the core material 4 is inserted relative to the cement grout 13 with its smaller diameter side facing downwards, away from the lower end of the cement grout 13, and with its larger diameter side protruding upwards from the ground 2 so that a pile cap 5 (Figures 1(a) and 1(b)) can be attached. Then, the cement grout 13 is allowed to harden to form the cement section 3 as shown in Figure 4(e). In this case, for example, a screw is used as the excavation head of the excavator 10.

[0032] Another method involves, for example, positioning the excavator 10 at the excavation site in the ground 2 as shown in Figure 5(a), and performing preliminary excavation with the excavator 10 to form a borehole 11 to the target depth as shown in Figure 5(b). Then, as shown in Figure 5(c), injecting cement grout 13 into the borehole 11 while repeatedly moving the excavator 10 up and down in the borehole 11, and as shown in Figure 5(d), inserting the core material 4 into the cement grout 13 with its smaller diameter side facing downwards, away from the lower end of the cement grout 13, and with its larger diameter side protruding upwards from the ground 2 so that a pile cap 5 (Figures 1(a) and 1(b)) can be attached. Finally, the cement grout 13 is allowed to harden to form the cement section 3 as shown in Figure 5(e). In this case, for example, a drum-type agitator is used as the excavation head of the excavator 10.

[0033] The bearing capacity mechanism of the ground improvement body 1 of this embodiment, constructed in this manner, will now be described.

[0034] In the ground improvement body 1, a vertical load acting on the upper end portion 4a of the core material 4 generates a lateral expansion pressure P in the tapered portion of the core material 4 as a wedge effect (hereinafter referred to as the tapered effect), and the resistance to this pressure corresponds to the bearing capacity.

[0035] This lateral expansion pressure P does not depend on the ground strength around the cement portion 3 of the ground improvement body 1.

[0036] The cement portion 3 on the circumferential surface of the core material 4 undergoes splitting failure due to the tapering 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 portion 3.

[0037] R f =β·σ y ·π·(D c -d ave )·L / 4 / 1000 ···(1)

[0038] Here, R f σ is the bearing capacity [kN], β is the correction factor (0.75~1.00), σ yis the splitting tensile strength [N / mm 2 , D c is the diameter [mm] of the cement part 3, d ave is the average diameter [mm] of the core material 4, and L is the length [mm] of the cement part 3. Note that the average diameter d ave of the core material 4 is the maximum diameter of the core material 4. In this embodiment, the diameter of the upper end portion 4a (the end mouth) is D0 [mm], and the minimum diameter of the core material 4, in this embodiment, the diameter of the lower end portion 4b (the original mouth) is D [mm]. Then, d ave =(D0 + D) / 2 is obtained.

[0039] In this embodiment, preferably, the diameter D c of the cement part 3 is 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 of the cement part 3 is 400 to 700 mm. When the maximum diameter D0 of the core material 4 is 450 mm, the diameter D c of the cement part 3 is 900 to 1500 mm. Also, the length L of the cement part 3 is, for example, 15 m, and the maximum length of the core material 4 is also the same 15 m as the length L of the cement part 3.

[0040] Thus, according to one embodiment, the ground improvement body 1 embeds a long concrete core material 4 in which the upper end portion 4a is formed with a larger diameter than the lower end portion 4b in the cement part 3 buried in the ground 2. Due to the vertical load acting on the core material 4, a lateral expansion pressure P is generated from the core material 4 to the cement part 3, and the resistance to this can be generated as a supporting force. By positioning the lower end portion 4b of the core material 4 above the lower end portion 3b of the cement part 3, a surplus portion 3c of the cement part 3 is formed below the lower end portion 4b of the core material 4. Therefore, even after the cement part 3 is split and broken due to the lateral expansion pressure P (taper effect), an axial force remains in this surplus portion 3c, so brittle failure like when the ground 2 is broken does not occur. Also, even if the cement part 3 is split and broken due to the lateral expansion pressure P (taper effect), the cement part 3 itself is supported by the surrounding ground, so brittle failure like when the ground 2 is broken does not occur.

[0041] Furthermore, by leaving the upper end portion 4a of the core material 4 above the ground 2, the pile cap 5 can be embedded in the upper end portion 4a of the core material 4, thereby ensuring horizontal force for the superstructure.

[0042] Therefore, compared to cases such as using steel pipes as core materials, it is possible to provide a ground improvement body 1 that is inexpensive and has excellent bearing capacity and horizontal force resistance.

[0043] Furthermore, since the core material 4 is tapered, gradually increasing in diameter from the lower end 4b to the upper end 4a, it can effectively generate lateral expansion pressure P, and can also effectively utilize discarded utility poles, for example, as the core material 4.

[0044] Furthermore, regardless of the strength of the ground 2 surrounding and below the cement section 3, even in the case of extremely soft ground 2, 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.

[0045] Furthermore, when inserting the core material 4 into the soil cement 12 or cement milk 13, the volume expansion due to the pressure during insertion also contributes to increasing the taper effect, thereby improving the bearing capacity of the ground improvement body 1.

[0046] Furthermore, by constructing multiple ground improvement bodies 1 in the ground 2, such as by constructing them as individual piles as shown in Figure 2(a), walls as shown in Figure 2(b), grids as shown in Figure 2(c), or blocks as shown in Figure 2(d), they can be used for liquefaction countermeasures, retaining walls, and earth pressure resistant structures.

[0047] Furthermore, since the bearing capacity of the ground improvement body 1 can be designed using the bearing capacity calculation formula (1) above based on the splitting tensile strength of the cement portion 3, it becomes possible to freely design the superstructure according to the ground pressure based on the strength and geometric dimensions of the cement portion 3, regardless of the hardness of the ground 2.

[0048] The splitting tensile strength of cement section 3 can be calculated from laboratory experiments by collecting soil samples from the site. Therefore, the bearing capacity of the ground improvement body 1 can be easily designed using the bearing capacity calculation formula (1) above without the need for large-scale ground investigations, enabling low-cost design.

[0049] Furthermore, 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 confirm whether the bearing capacity of the ground improvement body 1 satisfies the design value using the bearing capacity calculation formula (1) described above. This makes it easy to conduct a comprehensive survey of all ground improvement bodies 1 using this method without performing load tests, enabling low-cost and high-quality quality control.

[0050] Next, with reference to Figures 6 to 8, we will explain a simulated test demonstrating the validity of the above bearing capacity calculation formula (1).

[0051] As shown in Figure 6, the tapered pile 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 (taper angle 0.42°), meaning the average diameter d ave A tapered pile with a diameter of 66.5 (=(70+63) / 2) mm was used as the core material 4. As shown in Figures 7(a) and 7(b), the core material 4 was inserted into each cement section 3 and embedded in the test specimens. For test conditions No. 1 to No. 14, the calculated values ​​obtained from the bearing capacity calculation formula (1) using the splitting tensile strength of the cement section 3 were compared with the measured values ​​of the push-out resistance.

[0052] The test specimen was constructed using steel, such as SS400, for the core material 4. For the cement section 3, void tubes 16 were placed on the bottom plate 15, and soil cement or cement grout was filled inside them as a solidifying agent. As for the soil cement, a mixture of Kasaoka clay and silica sand No. 6 was used. The amount of solidifying agent added C was 300 kg / m³ in each case. 3Each was set to have a water-cement ratio (W / C) of 80%. The material of the bottom plate 15 was 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 pressing of the core material 4. The diameter of the opening 15a was, for example, φ130 mm. In addition, a void tube 16 with a height of 500 mm and a thickness of 4 mm was used. In other words, the length (L) of the cement section 3 is 500 mm. Furthermore, the inner diameter of the void tube 16, i.e., the diameter (D) of the cement section 3 c For the ), we used those measuring 150-250 mm, as shown in Table 1.

[0053] [Table 1]

[0054] Furthermore, in order to test the influence of the excess reinforcement portion 3c below the lower end 4b of the core material 4 on the bearing capacity calculation formula (1) relative to the lower end 3b of the cement portion 3, a test specimen with the excess reinforcement portion 3c (Figure 7(a)) and a test specimen without the excess reinforcement portion (Figure 7(b)) were used. The length of the excess reinforcement portion 3c was set to 70 mm.

[0055] And for the above test conditions No. 1 to No. 14, the splitting tensile strength σ y Figure 8 shows a comparison between the bearing capacity calculated based on the bearing capacity calculation formula (1) with a correction factor β = 0.75, and the measured value of the piercing resistance measured by applying a piercing load Pi to the upper end 4a of the core material 4.

[0056] As shown in Figure 8, the calculated values ​​are generally close to the measured values, and in particular, when soil cement is used as the solidifying agent, the calculated values ​​and measured values ​​are extremely close. Therefore, the validity of the bearing capacity calculation formula (1) above has been demonstrated. Regarding the presence or absence of the excess reinforcement section, although the impact on the bearing capacity calculation formula (1) was not clearly shown, the presence of the excess reinforcement section 3c resulted in greater push-out resistance.

[0057] Next, we will describe a test that demonstrates the difference in bearing capacity depending on the presence or absence of the core material 4 in the ground improvement body 1.

[0058] First, soil cement was injected while excavating a borehole into the ground, and the borehole was drilled to the target depth while mixing it with the local soil. A concrete pole (tapered pile) was then sunk into the unsolidified soil cement as core material 4. Core material 4 was a tapered pile (taper angle 1 / 75°) with a total length of 8m, a diameter (D0) of 190mm at the upper end 4a and a diameter (D) of 297mm at the lower end 4b, and a bending crack resistance of 5kN was used. The excavation diameter of the borehole, i.e., the diameter (D) of the cement section 3, was used. c The borehole length was set to 800 mm, and the length of the drilled hole, i.e., the length of cement section 3 (L), was set to 8 m. The splitting tensile strength (σ) of cement section 3 was confirmed by taking soil cement samples from the site. y ) is 0.107 N / mm 2 Furthermore, when the correction coefficient β is set to 0.75, the bearing capacity (R) can be calculated from these values ​​using the bearing capacity calculation formula (1) above. f The power output was 281 kN.

[0059] First, it was confirmed that the core material 4 could be fixed without any problems to the cement section 3 where the soil cement had hardened.

[0060] Next, a plate load test was conducted on cement section 3, where the soil cement had solidified, at 28 days of age using heavy machinery. The applied load and displacement were measured to confirm the applied load relative to the bearing capacity calculated using the bearing capacity calculation formula (1) above. Test conditions No. 15 to No. 17 implemented in the test are shown in Table 2.

[0061] [Table 2]

[0062] As shown in Figure 9, for test conditions No. 15 and 16 using core material 4, the bearing capacity R was calculated using the bearing capacity calculation formula (1) above for each load. f There is almost no displacement until the load is supported by bearing force R. fThe cement section 3 fractured when the load exceeded 281kN (approximately 310-315kN). However, the decrease in load after reaching that point was gradual. This is thought to be because even after the cement section 3 fractured, axial force remained in the remaining cement section 3 and the excess pile 3c below the core material 4, and because the cement section 3 itself was supported by the surrounding ground, brittle fracture did not occur.

[0063] In contrast, under test condition No. 17, which did not use core material 4, yielding occurred at a load of approximately 140 kN.

[0064] As a result, it was shown that embedding the core material 4 in the cement section 3 with an excess pile section 3c significantly increases the bearing capacity of the ground improvement body 1. [Explanation of symbols]

[0065] 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 boreholes 12 Soil Cement 13 Cement Milk

Claims

1. A columnar cement section embedded in the ground, It comprises a long concrete core material embedded in the cement portion, with the upper end having a larger diameter than the lower end, The core material is tapered, gradually increasing in diameter from the lower end to the upper end, with the upper end protruding upward relative to the upper end of the cement portion and the ground. The pile cap further comprises the upper end of the cement portion and the upper end of the core material that protrudes upward from the ground into which the upper end of the core material is embedded. A ground improvement body characterized by the following features.

2. The core material is positioned with its lower end separated above the lower end of the cement portion. The ground improvement body according to claim 1.

3. A method for constructing a ground improvement body on the ground, comprising a columnar cement section, a long concrete core material with one end having a larger diameter than the other end, and a pile cap into which one end of the core material is embedded, While excavating a borehole in the aforementioned ground, a cement-based solidifying agent 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 with the other end facing downwards and one end protruding upwards from the ground. The soil cement is hardened to form the cement portion. The pile cap is attached so as to embed the upper end of the cement portion and the one end of the core material that protrudes upward from the ground. A method for constructing a ground improvement body characterized by the following features.

4. When inserting the core material into the soil cement, the other end of the core material is inserted so that it is separated upward from the lower end of the soil cement. A method for constructing a ground improvement body as described in feature 3.

5. A method for constructing a ground improvement body on the ground, comprising a columnar cement section, a long concrete core material with one end having a larger diameter than the other end, and a pile cap into which one end of the core material is embedded, Cement grout is injected into the borehole formed in the ground. Before the cement grout hardens, the core material is inserted into the cement grout with the other end facing downwards and one end protruding upwards from the ground. The cement milk is hardened to form the cement portion. A pile cap is attached so as to embed the upper end of the cement portion and the one end of the core material that protrudes upward from the ground. A method for constructing a ground improvement body characterized by the following features.

6. When inserting the core material into the cement grout, the other end of the core material is inserted so that it is separated upward from the lower end of the cement grout. A method for constructing a ground improvement body according to feature 5.

7. Multiple ground improvement structures are placed side by side and constructed on the ground. A method for constructing a ground improvement body according to claim 3 or 5, characterized by the features described above.

8. A method for designing a ground improvement body to be constructed by the ground improvement body construction method described in claim 3 or 5, The bearing capacity of the ground improvement body is designed based on the splitting tensile strength of the cement portion of the ground improvement body. A method for designing a ground improvement body, characterized by the following features.

9. A method for controlling the quality of a ground improvement body constructed by the ground improvement body construction method described in claim 3 or 4, the method comprising: By calculating the splitting tensile strength of the cement portion of the ground improvement body from the soil cement sampled during construction, it is determined whether or not the bearing capacity satisfies the predetermined design value. A method for quality control of ground improvement bodies characterized by the following features.

10. A method for controlling the quality of a ground improvement body constructed by the construction method of a ground improvement body described in claim 5 or 6, the method comprising: By calculating the splitting tensile strength of the cement portion of the ground improvement body from the cement grout sampled during construction, it is determined whether or not the bearing capacity satisfies the predetermined design value. A method for quality control of ground improvement bodies characterized by the following features.

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