Pile body for the outer excavation and foundation reinforcement method and outer excavation and foundation reinforcement method

Abstract

To provide a pile for an outer excavated foot protection method, and an outer excavated foot protection method, which are capable of improving the integrity between a pile tip part and a foot protection part.SOLUTION: A pile 1 for an outer excavated foot protection method is installed in a pile hole 5 in a straight shape. The pile 1 is provided wit a cylindrical concrete pile body 2 and a plurality of groove parts 3 having groove bottom parts with diameters smaller than that of the pile body 2 arranged on an outer peripheral surface of a support layer foot penetration part of the pile body 2. The groove part 3 has a taper part 3a on a corner part. All of the number thereof in accordance with a pile diameter D are within a length from a tip part of the pile body 2 installed in a support layer 8 to a length equal to a pile diameter D.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a pile body for an external excavation ground improvement method and an external excavation ground improvement method.

Background Art

[0002] Conventionally, in the external excavation ground improvement method, a straight pile hole having the same diameter over the entire length is excavated in the ground, a ground improvement liquid and a pile circumference fixing liquid are sequentially injected into the pile hole, a precast pile is sunk, and the ground improvement liquid and the pile circumference fixing liquid are solidified to form a ground improvement part and a pile circumference fixing part on the outer periphery of the pile (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the case of the above external excavation ground improvement method, when a vertical load acts on the tip of the pile, the load is transmitted to the ground improvement part by the adhesive force from the inner and outer surfaces of the pile and the bearing pressure of the bottom surface of the pile through the pile. Then, the load is transmitted from the circumferential surface and the bottom surface of the ground improvement part to the ground improvement part, the pile and the ground improvement part behave integrally, and are transmitted from the circumferential surface and the bottom surface of the ground improvement part to the supporting ground.

[0005] Therefore, in order to effectively transmit the vertical load to the supporting ground, it is desirable to improve the integrality between the tip of the pile and the ground improvement part.

[0006] The present invention has been made in view of such points, and an object thereof is to provide a pile body for an external excavation ground improvement method and an external excavation ground improvement method capable of improving the integrality between the tip of the pile and the ground improvement part.

Means for Solving the Problems

[0007] The pile body for the external excavation and foundation reinforcement method described in claim 1 is a pile body for the external excavation and foundation reinforcement method that is sunk into a straight-shaped pile hole, comprising a cylindrical concrete pile body and a plurality of grooves provided on the outer circumferential surface of the portion of the pile body embedded in the supporting layer, each having a groove bottom smaller in diameter than the outer diameter of the pile body, wherein the grooves have tapered portions at their corners, and all of the grooves, in a number corresponding to the pile diameter, are located within a range equal to the pile diameter from the tip of the pile body embedded in the supporting layer. Furthermore, the long-term allowable shear stress of the concrete of the pile body is 1.65 N / mm². 2 In summary, the short-term allowable shear stress is 2.48 N / mm². 2 That's all. It is.

[0008] The pile body for the external excavation and foundation reinforcement method described in claim 2 is the pile body for the external excavation and foundation reinforcement method described in claim 1, wherein all grooves are provided with the same shape and dimensions, and the number of grooves is set according to the pile diameter.

[0009] The pile body for the outer excavation and foundation reinforcement method described in claim 3 is the pile body for the outer excavation and foundation reinforcement method described in claim 1, The outer circumferential area of ​​the pile body between grooves is larger than the outer circumferential area of ​​the grooves, and the ratio of their areas is between 1.53 and 4.11. It is.

[0010] The external excavation and foundation reinforcement method described in claim 4 is a pile body for the external excavation and foundation reinforcement method described in any one of claims 1 to 3, comprising the steps of: forming a straight-shaped pile hole; injecting a foundation reinforcement liquid into the support layer portion of the pile hole; further injecting a pile periphery fixing liquid into the pile hole; sinking the pile body described in any one of claims 1 to 3 into the pile hole; and solidifying the foundation reinforcement liquid and the pile periphery fixing liquid to form a foundation reinforcement portion and a pile periphery fixing portion on the outer circumference of the pile body.

[0011] The external excavation and foundation reinforcement method described in claim 5 is the external excavation and foundation reinforcement method described in claim 4, wherein the outer diameter of the foundation reinforcement section is 1.33 times or more and 1.35 times or less the pile diameter, and the height of the foundation reinforcement section below the tip of the pile body is 1.2 times the pile diameter. [Effects of the Invention]

[0012] According to the present invention, it becomes possible to improve the integration between the pile tip and the base reinforcement portion. [Brief explanation of the drawing]

[0013] [Figure 1] This is a cross-sectional view of a pile body used for an external excavation and foundation reinforcement method according to one embodiment of the present invention during pile construction. [Figure 2] This is an enlarged side view of a portion of one example of the pile structure shown above. [Figure 3] This is an enlarged side view of a portion of another example of the same pile structure. [Figure 4] This is a side view showing the relationship between the outer circumferential area As1 of the groove portion in the pile body and the outer circumferential area As2 of the pile body sandwiched between the groove portions. [Figure 5] This is a cross-sectional view showing the relationship between the outer circumferential area As1 of the groove portion in the pile body and the outer circumferential area As2 of the pile body sandwiched between the groove portions. [Figure 6] These are half-section views showing examples of the same pile body, with (a) showing an example with a pile diameter of φ300 mm, (b) showing an example with a pile diameter of φ350 mm, (c) showing an example with a pile diameter of φ400 mm, and (d) showing an example with a pile diameter of φ450 mm. [Figure 7] These are half-section views showing examples of the same pile body, with (a) showing an example with a pile diameter of φ500 mm, (b) showing an example with a pile diameter of φ600 mm, and (c) showing an example with a pile diameter of φ700 mm. [Figure 8] These are half-section views showing examples of the same pile body, with (a) showing an example with a pile diameter of φ800 mm, (b) showing an example with a pile diameter of φ900 mm, and (c) showing an example with a pile diameter of φ1000 mm. [Figure 9] The above is a half-section view showing an example of a pile body; (a) shows an example with a pile diameter of φ1100 mm, and (b) shows an example with a pile diameter of φ1200 mm. [Figure 10] These are explanatory cross-sectional views showing the same external excavation and foundation reinforcement method in the order of (a) to (e). [Figure 11] This is a cross-sectional view of test specimen A, which does not have a groove. [Figure 12] This is a cross-sectional view of specimen B, which has two grooves with a groove depth of 3 mm. [Figure 13] This is a cross-sectional view of test specimen C, which has two grooves with a groove depth of 7 mm. [Figure 14]This is an explanatory diagram showing the procedure for performing load testing on a test specimen. [Figure 15] This is a characteristic diagram of the test results showing the relationship between the adhesion strength and pile head displacement of test specimen A-1. [Figure 16] This is a characteristic diagram of the test results showing the relationship between the adhesion strength and pile head displacement of test specimen A-2. [Figure 17] This is a characteristic diagram of the test results showing the relationship between the adhesion strength and pile head displacement of test specimen B-1. [Figure 18] This is a characteristic diagram of the test results showing the relationship between the adhesion strength and pile head displacement of test specimen B-2. [Figure 19] This is a characteristic diagram of the test results showing the relationship between the adhesion strength and pile head displacement of test specimen C-1. [Figure 20] This is a characteristic diagram of the test results showing the relationship between the adhesion strength and pile head displacement of test specimen C-2. [Modes for carrying out the invention]

[0014] Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

[0015] Figure 1 shows a pile body labeled 1. The pile body 1 shows a cross-section constructed using the external excavation and enlarged foundation reinforcement method. The pile body 1 is a precast concrete pile, and is constructed by forming multiple grooves (recessed grooves) 3 on the outer surface of the supporting layer embedded portion at the tip of the reinforced cylindrical concrete pile body 2, each groove having a smaller diameter bottom than the outer diameter of the pile body 2. A steel pipe fitting 4 is attached to the tip of the pile body 2 to temporarily reduce the frictional force on the outer surface of the pile and facilitate pile insertion. This pile body 1 is installed in a straight pile hole 5 along its entire length, and the foundation pile structure is formed by the foundation reinforcement portion (foundation reinforcement bulb portion) 6 formed at the tip of the pile and the pile perimeter fixing portion 7 formed around the pile.

[0016] In this construction method, when a vertical load acts on the pile tip, it is transmitted to the foundation reinforcement section 6 from the pile's circumferential and bottom surfaces, causing the pile body 2 and the foundation reinforcement section 6 to act as a single unit, and the load is transmitted to the supporting ground from the circumferential and bottom surfaces of the foundation reinforcement section 6. The pile tip bearing capacity is defined as the axial force (P) acting on the pile tip and the bearing capacity (P) of the ground at the lower end of the foundation reinforcement section 6. b ) and the circumferential friction force (P) of the root reinforcement part 6 fb ) is supported by the following: That is, P = P b +P fb ...(Equation 1).

[0017] In this construction method, the frictional force of the reinforcing section 6 embedded in the underground support layer 8 is high because of the high ground strength. Therefore, by increasing the frictional force between the reinforcing section 6 and the pile body 1, and improving the unity between the tip of the pile body 1 embedded in the support layer 8 and the reinforcing section 6, the frictional force between the support layer 8 and the reinforcing section 6 can be effectively utilized as the bearing capacity of the pile body 1.

[0018] The thickness t of the pile body 2 shall be equal to or greater than the thickness specified in "JIS A 5373:2010 Precast Prestressed Concrete Products Recommended Specifications E-1".

[0019] For the pile diameter D, for example, a diameter of φ300 mm to φ1200 mm is preferably used. The outer diameter Do of the base reinforcement section 6 is standardly 1.33 times the pile diameter D, and is rounded to the nearest 10 mm. Table 1 shows examples of the relationship between the pile diameter D and the outer diameter Do of the base reinforcement section 6 in this embodiment. In these examples, the outer diameter Do of the base reinforcement section 6 is 1.33 to 1.35 times the pile diameter D. In the table, Di is the inner diameter of the pile, and H1 is the required height of the base reinforcement section below the pile tip.

[0020] [Table 1]

[0021] In this embodiment, since the pile hole 5 is formed in a straight shape with the same diameter along its entire length, the outer diameter Do of the foundation reinforcement portion 6 is equal to the diameter of the pile hole 5.

[0022] The groove 3 is formed to improve integration with the foundation reinforcement section 6. In this embodiment, the groove 3 has tapered sections 3a formed at the upper and lower corners, which serve as corners, connecting the groove bottom with the outer surface of the pile body 2. Providing the tapered sections 3a is expected to reduce soil adhesion during pile insertion, and also to reduce the likelihood of underground obstacles getting caught in the groove 3 during pile insertion, thereby preventing damage to the groove 3.

[0023] The grooves 3 are positioned in the area where the pile tip is embedded in the support layer 8, and are formed on the outer surface of the pile from the pile tip to the section with a pile diameter of D. In this embodiment, the embedment length into the support layer 8 is greater than or equal to the pile diameter D. The spacing of the grooves 3 is set according to the pile diameter D to ensure integrity with the reinforcing material (mortar) formed in each groove 3 against the shear force generated by the vertical load acting on the pile body 1, and is, for example, spaced from 150 mm to 300 mm. Furthermore, the shape of the grooves 3 is such that, for a small pile diameter D, for example, the groove depth is 3 mm, and for a large pile diameter D, for example, the groove depth is 7 mm. As shown in Figure 2, in this embodiment, for pile bodies 1 with diameters of φ300 mm and φ350 mm, the groove depth is 3 mm, and as shown in Figure 3, for pile bodies 1 with diameters of φ400 mm to φ1200 mm, the groove depth is 7 mm. The groove width is 8 to 20 times the groove depth.

[0024] Furthermore, the number of grooves and shear strength of the grooves 3 shown in Figure 1 determine the frictional force and degree of friction that the grooves 3 embedded in the support layer 8 can withstand. In other words, the number of grooves and shear strength of the grooves 3 are set based on the frictional force and degree of friction that the grooves 3 embedded in the support layer 8 can withstand.

[0025] The number of the groove portions 3 is set according to the pile diameter D based on the results of the shear test of the groove portions 3. In the present embodiment, in the case of the pile body 1 with a pile diameter of φ300 mm to φ600 mm, there are two groove portions 3; in the case of the pile body 1 with a pile diameter of φ700 mm to φ900 mm, there are three groove portions 3; and in the case of the pile body 1 with a pile diameter of φ1000 mm to φ1200 mm, there are four groove portions 3.

[0026] Also, the shear strength of the groove portion 3 of the present embodiment is set in consideration of the theoretical compression strength of the root consolidation portion 6. Here, the average N value of the ground near the pile tip and the axial force (= α·N·A p =π·D 2 / 4, D is the pile diameter) obtained therefrom act on the α calculation position 9, and the frictional force (P p ) in the section where the pile body 2 is fixed to the root consolidation portion 6 causes the attenuated axial force (= the bearing resistance (P fa )) at the pile tip to act on the pile tip. This attenuated axial force is transmitted to the root consolidation portion 6, and the root consolidation portion 6 below the pile tip is in a bearing state. Therefore, the theoretical compression strength of the root consolidation portion 6 required for the bearing strength (F a ) acting on the pile tip (α calculation position 9) is obtained. B ) is obtained.

[0027] The bearing strength (F B ) acting on the pile tip is the value obtained by dividing the bearing resistance (P a ) acting on the pile tip by the bearing area (A2) (= P a / A2). The bearing area is equal to the closed cross-sectional area (A p ) of the pile tip. Also, for the theoretical compression strength (F C ) of the root consolidation portion 6, from the bearing test results, the bearing strength (F B ), the bearing area (A2), and the bearing area (A k), and the relationship between the compressive strength of the foundation reinforcement section 6 is used. For the bearing test, the results obtained from "Chapter VI 5. Foundation tests conducted in the performance evaluation 5.3 Bearing test" conducted in the BCJ Basic Evaluation-FD0069-03 (MRXX construction method) of the Japan Building Center, a general incorporated foundation, on March 22, 2006, are used. That is, the difference in bearing strength when the bearing area of ​​the test specimen is kept constant and the bearing area is changed was examined, and it was found that as the bearing area / bearing area ratio increases, the bearing strength tends to increase, so a regression equation and a lower limit of the 95% confidence interval were obtained from the test results. The following equation obtained from these results is adopted.

[0028] F B / F C =(Ak / A2) 0.29 Therefore, F C =F B / ( A k / A2) 0.29

[0029] Using the bearing capacity coefficient α = 417, the axial force acting on the pile tip (α calculation position 9) at the average N-value of the ground near the pile tip (= 60) is determined. Subtracting this force from the frictional force of the pile anchored to the base reinforcement section 6 gives the bearing capacity of the pile tip. The resulting bearing strength is 17.2 N / mm². 2 Therefore, calculating the theoretical compressive strength of the foundation reinforcement section 6 from the above formula, we get 14.5~14.6 N / mm², as shown in Table 2. 2 This is the result.

[0030] [Table 2]

[0031] Regarding the bearing capacity coefficient α, the Architectural Institute of Japan's "Report of the Subcommittee on Vertical Bearing Capacity of Piles," August 2008, in "Chapter 2: Tip Bearing Capacity, 2.5 Analysis of Tip Surface Bearing Capacity Focusing on Construction Methods and Tip Shapes of Piles, 2.5.2 Embedded Piles (High Bearing Capacity Piles)," evaluates that "the α value at the tip of the base reinforcement portion of an embedded pile is considered to be a reasonable value of 150 to 200, although this depends on the pile diameter." Therefore, based on the above Equation 1, when an axial force equivalent to a bearing capacity coefficient α = 417 is applied, the bearing capacity coefficient α0 (=P) of the ground at the tip of the pile when the average N value of the ground near the tip of the pile is 60 is... b / (N·A0), where A0 is the cross-sectional area of ​​the base reinforcement part 6 (=π·Do 2 The values ​​(τ) of the circumferential friction force of the base reinforcement section 6 are determined for each pile diameter (see Table 3), and these values ​​are adopted based on the fact that they fall within the range of reasonable values ​​mentioned above. f For ), we adopted 6.5N (from the panel discussion and keynote speech materials of the Structural Engineering Division (Foundation Structure) at the 2007 Architectural Institute of Japan Convention (Kyushu).

[0032] [Table 3]

[0033] Therefore, based on this theoretical compressive strength, the set compressive strength of the foundation reinforcement section 6 is set to, for example, 14.60 N / mm². 2 Based on the results of the shear test of groove 3, the ratio of the shear strength of groove 3 to the mortar strength of the 7-day-old specimen is 0.26 to 0.29, therefore the shear strength of groove 3 is 3.79 (= 14.60 × 0.26) N / mm². 2 Let's assume that.

[0034] Table 4 shows examples of the frictional force and degree of friction that the groove portion embedded in the support layer 8 can withstand under these conditions. In this embodiment, the upper limit of the degree of friction that the portion embedded in the support layer 8 can withstand is 0.76 N / mm². 2 ~1.52 N / mm 2 That is the case.

[0035] [Table 4]

[0036] Furthermore, as shown in Figures 4 and 5, the outer perimeter area As2 of the pile body 2 sandwiched between the upper and lower grooves 3, 3 is larger than the outer perimeter area As1 of the groove 3. In other words, if we consider the shear strength of the pile concrete on the safe side and set it to be the same as the shear strength of the grouting material (mortar), then for the pile body 2 to be safe against the axial force borne in the groove 3, the outer perimeter area As2 of the pile body 2 must be greater than or equal to the outer perimeter area As1 of the groove 3. In this case, the shear resistance area of ​​the pile body 2 will be larger than the shear resistance area of ​​the grouting material in the groove 3, and the pile body 2 will not be damaged by the shear stress τ. Table 5 shows examples of each pile diameter D, outer perimeter area As1, outer perimeter area As2, and their ratios, i.e., area ratios, in this embodiment. In these examples, the area ratios are 1.53 to 4.11, and the pile body 1 will not be damaged by shear force.

[0037] [Table 5]

[0038] Furthermore, when the ultimate vertical load acts on the pile body 1, the maximum shear force P acts on the upper concrete portion of the groove 3 (the portion extending from the upper tapered portion 3a of the groove 3 to the lower tapered portion 3a of the grooves lined up above the groove 3 (the range of As2 shown in Figures 4 and 5)) via the reinforcing portion 6 filled in the groove 3. max The shear strength τ of the groove 3 is u It is calculated by the product of the area As1 of the outer perimeter of the groove 3. At this time, the shear stress τ generated in the concrete portion at the top of the groove 3 max P is the maximum shear force. max The shear strength τ of the groove 3 can be obtained by dividing it by the outer perimeter area As2. u Divide this by the ratio of the area of ​​the outer perimeter As2 to the area of ​​the outer perimeter As1 (τ max =τ u This shear stress τ is calculated by (As2 / As1). maxThis is the maximum value under the application of the ultimate vertical load, and since the shear stress in the pile body 1 will not exceed this even under the application of the short-term allowable axial force, as a safety measure, the concrete portion at the top of the groove 3 will have the required short-term allowable shear stress τ. a2 This shear stress τ max Set to this.

[0039] Furthermore, according to Article 8, Paragraph 1, Item 5 of Notification No. 1113 of the Ministry of Land, Infrastructure, Transport and Tourism, the long-term allowable shear stress τ of the concrete portion at the top of the groove 3. a1 and short-term allowable shear stress τ a2 The ratio is 1:1.5.

[0040] Based on the conditions for a pile with a diameter of 300 mm in the example shown in Table 3 of this embodiment, the allowable shear stress of the concrete is the long-term allowable shear stress τ a1 1.65 N / mm 2 The above is the short-term allowable shear stress τ a2 2.48 N / mm 2 The above materials will be used. For example, the design strength (F) of the concrete used for pile body 2 is 105 N / mm². 2 According to Article 8, Paragraph 1, Item 5 of Notification No. 1113 of the Ministry of Land, Infrastructure, Transport and Tourism, the allowable shear stress of the concrete portion at the top of the groove 3 (long-term allowable shear stress τ) c1 , short-term allowable shear stress τ c2 )teeth, τ c1 = 1.2 N / mm 2 τ c2 = 1.8 N / mm 2 Therefore, the long-term and short-term shear forces Q acting on the concrete portion at the top of the groove 3 and the allowable shear stress Q of the concrete portion at the top of the groove 3 are determined. a When comparing them, (long term) Q=τ a1 As1 = 1.65 × 56549 = 93306 (N) Q a =τ c1 As² = 1.2 × 86821 = 104185 (N) (short term) Q=τ a2 As1 = 2.48 × 56549 = 140242 (N) Q a =τ c2 As² = 1.8 × 86821 = 156277 (N) Therefore, all are Q a Therefore, by using concrete with the above-mentioned allowable shear stress, the concrete portion at the top of the groove 3 will not be damaged.

[0041] Based on the above considerations, examples of pile bodies 1 in this embodiment are shown in Figures 6 to 9. Figure 6(a) shows an example of a pile body 1 with a diameter of φ300 mm, Figure 6(b) shows an example of a pile body 1 with a diameter of φ350 mm, Figure 6(c) shows an example of a pile body 1 with a diameter of φ400 mm, and Figure 6(d) shows an example of a pile body 1 with a diameter of φ450 mm. Figure 7(a) shows an example of a pile body 1 with a diameter of φ500 mm, Figure 7(b) shows an example of a pile body 1 with a diameter of φ600 mm, and Figure 7(c) shows an example of a pile body 1 with a diameter of φ700 mm. Figure 8(a) shows an example of a pile body 1 with a diameter of φ800 mm, Figure 8(b) shows an example of a pile body 1 with a diameter of φ900 mm, and Figure 8(c) shows an example of a pile body 1 with a diameter of φ1000 mm. Figure 9(a) shows an example of pile body 1 with a pile diameter of φ1100 mm, and Figure 9(b) shows an example of pile body 1 with a pile diameter of φ1200 mm.

[0042] As shown in these examples, multiple grooves 3 of the same shape and dimensions are provided for each pile body 1, and the number of grooves increases or decreases according to the pile diameter D. The width of the grooves 3 is set to a constant value considering the shear strength of the foundation reinforcement material (mortar) within the grooves 3, and the depth of the grooves 3 is set to a constant value considering the amount of concrete cover up to the reinforcement of the pile body 2. By making the shape (dimensions) of the grooves 3 the same in this way, the cost of pile manufacturing (formwork) is reduced.

[0043] Next, the effects and advantages of this embodiment will be explained.

[0044] ​In this embodiment of the external excavation and foundation reinforcement method, first, as shown in Figure 10(a), a straight-shaped pile hole 5 is excavated and formed. At this time, the excavation center of the auger (excavation and mixing device) 10 is aligned with the pile center, and while injecting water or the like, the auger 10 is moved up and down as needed to excavate down to the lower end of the foundation reinforcement in the supporting ground.

[0045] Next, as shown in Figure 10(b), the root-stabilizing liquid 11 is injected into the support layer 8 portion of the pile hole 5. For example, after injecting half to the entire amount of the root-stabilizing liquid 11 at the lower end of the root-stabilizing section, the auger 10 is moved up and down a predetermined number of times, for example, twice, within the upper section, for example, within a range of 1.7 times the pile diameter D, and after injecting the entire amount of root-stabilizing liquid 11, the auger 10 is moved up and down along the entire length of the root-stabilizing section 6 as needed.

[0046] Furthermore, as shown in Figure 10(c), pile-peripheral fixing fluid 12 is injected into the pile hole 5. At this time, for example, the auger 10 is raised while injecting the pile-peripheral fixing fluid 12 from the lower end depth to the upper end depth of the injection range, and the auger 10 is raised and lowered at least once within the injection range. After that, the auger 10 is raised from the pile hole 5.

[0047] Subsequently, as shown in Figure 10(d), the pile body 1 is erected in the pile hole 5 and sunk to a predetermined depth.

[0048] Then, the root reinforcement liquid 11 and the pile perimeter fixing liquid 12 are solidified to form the root reinforcement portion 6 and the pile perimeter fixing portion 7 on the outer circumference of the pile body 1, as shown in Figure 10(e).

[0049] When a vertical load is applied to the pile tip (α calculation position 9) of the pile body 1, as shown in Figure 1, the load is transmitted from the pile circumferential surface and bottom surface within the base reinforcement section 6 to the base reinforcement section 6. The pile body 1 and the base reinforcement section 6 then behave as a single unit, and the load is transmitted from the bottom surface of the base reinforcement section 6 to the supporting ground.

[0050] In this case, for the entire cross-sectional area of ​​the bottom surface of the foundation reinforcement section 6 to function effectively, the ratio of the outer diameter Do of the foundation reinforcement section 6 to the pile diameter D (width ratio) and the ratio of the height H1 of the foundation reinforcement section 6 to the pile diameter D (height ratio) are relevant. Examples of width ratios and height ratios in the pile body 1 of this embodiment are shown in Table 6.

[0051] [Table 6]

[0052] In this embodiment, the width ratio is 1.33 as standard, and the height ratio is 1.20, which allows the entire cross-sectional area of ​​the bottom surface of the foundation reinforcement section 6 to be effectively utilized.

[0053] Furthermore, the groove 3 ensures the integrity of the pile body 2 and the base reinforcement section 6.

[0054] Therefore, when a vertical load is applied to the pile body 2, the shear force can be effectively transmitted to the supporting layer 8 via the root reinforcement portion 6, which is integrated in the groove portion 3 provided on the outer circumferential surface of the supporting layer embedded portion of the pile body 2.

[0055] By providing a tapered section 3a at the corner of the groove 3, the amount of soil adhering to the corner of the groove 3 during pile insertion can be reduced, and the resistance acting on the corner of the groove 3 from underground obstacles can be reduced, thereby preventing damage to the groove 3. Furthermore, by providing a tapered section 3a, the bearing area during pile installation can be increased, thereby reducing the bearing pressure, i.e., the stress load, and preventing damage to the groove 3 due to demolding during pile manufacturing, making demolding easier.

[0056] Even if the pile diameter changes, the shape and dimensions of the groove 3 remain unchanged. By increasing or decreasing the number of grooves, a common mold for forming the grooves can be used, thereby reducing the cost of manufacturing the piles.

[0057] By setting the long-term allowable shear stress of the concrete in the pile body 2 to 1.65 or higher and the short-term allowable shear stress to 2.48 or higher, it is possible to prevent the concrete in the upper part of the groove 3 from being damaged by shear force.

[0058] The outer surface area of ​​the pile body 2 between grooves 3, 3 is the groove 3Since the grooves are formed to be larger than the outer perimeter area, the shear resistance area between the grooves 3, 3 of the pile body 2 becomes larger than the shear resistance area of ​​the root reinforcement portion 6 formed within the grooves 3, thus preventing shear failure between the grooves 3, 3 of the pile body 2.

[0059] Since the outer diameter Do of the base reinforcement section is between 1.33 and 1.35 times the pile diameter D, and the height of the base reinforcement section 6 below the tip of the pile body 1 is 1.2 times the pile diameter D, the vertical load acting on the pile tip can be effectively transmitted to the supporting ground by utilizing the entire cross-sectional area of ​​the bottom surface of the base reinforcement section 6.

[0060] Next, the shear test of the groove 3 at the tip of the pile will be described with reference to Figures 11 to 20.

[0061] (1) Test Objectives The load at the pile tip is transmitted to the base reinforcement section 6 via the pile body 1 by the adhesion force from the inner and outer surfaces of the pile, as well as the bearing pressure at the lower end of the pile. Here, in order to increase the adhesion strength between the base reinforcement section 6 and the outer surface of the pile, a groove 3 is placed on the outer surface of the pile tip, and the adhesion strength between the pile body 1 and the base reinforcement section 6 is investigated.

[0062] (2) Examination Overview (a) Implementation details The test specimens were based on a pile body 2 with an outer diameter of φ200 mm and a length of 300 mm, with a base reinforcement section 6 formed on the outer surface, and a push-out test was performed. The test specimens consisted of two groove sections 3, with the groove sections 3 having two different depths of 3 mm and 7 mm. In addition, a straight-shaped test specimen without groove sections 3 was added, for a total of three types of concrete test specimens.

[0063] (b) Type of test specimen Table 7 shows test specimens A, B, and C used to investigate the adhesion strength between groove 3 and root reinforcement 6.

[0064] [Table 7]

[0065] (3) Preparation of test specimens (a) Test specimens for adhesion strength investigation The test specimens will be manufactured in the following cross-sectional shapes: mortar specimens A-1 and A-2 without grooves as shown in Figure 11; specimens B-1 and B-2 with two grooves 3 and a groove depth of 3 mm as shown in Figure 12; and specimens C-1 and C-2 with two grooves 3 and a groove depth of 7 mm as shown in Figure 13.

[0066] (b) Preparation of test specimens Formwork for pile body 1; for centrifugal specimens (φ200mm~300mm) Root reinforcement section, type 6 frame; PVC pipe (inner diameter φ286mm~250mm, thickness 16.2mm) Concrete mix for pile body 1; compressive strength is σ u = 105 N / mm 2 formulation Mortar mix for the base reinforcement section 6; Table 8

[0067] [Table 8]

[0068] The curing method used was air curing. Three test specimens (φ50mm to 100mm) were prepared for strength testing during the manufacturing process, and their strength was confirmed on the same day as the shear test.

[0069] (4) Test method As shown in Figure 14, the test method employed was an extrusion test method in which the test specimen was placed between a pressure receiving jig 15 and a pressurizing jig 16 and then pressurized.

[0070] Test machine; 500t Amsura Displacement measuring instrument; High-sensitivity displacement meter (50mm stroke) Loading method; continuous loading Measurement items: Load, pile head displacement (5) Summary of the results of the adhesion test The test results are shown in Table 9. The relationship between adhesion strength and displacement is shown in Figures 15 to 20.

[0071] [Table 9]

[0072] (a) Specimens A-1 and A-2, which lack grooves, failed due to linear displacement. Specimens B-1, B-2, C-1, and C-2, which have grooves, showed a temporary decrease in load after linear displacement, but the load increased again as the displacement progressed and reached its maximum value.

[0073] (b) The adhesion strength of the outer surface of the pile to the base reinforcement section 6 is the average compressive strength of 12.08 N / mm for mortar specimens A-1 and A-2, which do not have grooves 3. 2 In this case, the average adhesion strength is 0.77 N / mm². 2 Furthermore, the average compressive strength of the mortar specimens B-1 and B-2, with a groove depth of 3 mm, was 12.33 N / mm². 2 In this case, the average adhesion strength is 2.06 N / mm². 2 The average compressive strength of the mortar specimens C-1 and C-2, with a groove depth of 7 mm, was 12.35 N / mm². 2 In this case, the average adhesion strength is 2.01 N / mm². 2 Therefore, no significant difference in adhesion strength due to groove depth was observed.

[0074] (6) Friction force on the pile surface within the base reinforcement section 6 (τ ft Regarding the relationship between ) and the compressive strength (σ) of the root reinforcement section Based on the adhesion test results above, the frictional force on the pile surface within the base reinforcement section 6 (τ ft The relationship between ( ) and the compressive strength (σ) of the foundation reinforcement is calculated.

[0075] The shear force borne by groove 3 is determined by subtracting the adhesion force in the area excluding groove 3 from the test load. This calculation for the surface area excluding groove 3 is determined by adopting the average adhesion strength from the test results of test specimen A, which does not have groove 3. Therefore, the shear stress (τ) in the groove 3 area is m The shear force ) is calculated by dividing this shear force by the surface area of ​​the groove 3. The calculation formula is as follows.

[0076] τ m =P-(L0-L1)×π×D×τ st / (π×D×L1) Here, P is the test load (kN), D is the pile diameter (mm), L0 is the length (mm) in contact with the fixing part 6, L1 is the length (mm) of the groove part 3, and τ st is the shear stress intensity (N / mm 2 ) excluding the groove area. The average shear stress intensity τ st of the test specimens A-1 and A-2 is 0.77 N / mm 2 .

[0077] The shear stress intensity borne by the groove part 3 according to the experimental results is 3.70 N / mm 2 and 3.20 N / mm 2 for the test specimens B-1 and B-2 with a groove depth of 3 mm, and 3.72 N / mm 2 and 2.98 N / mm 2 for the test specimens C-1 and C-2 with a groove depth of 7 mm. The average value (τ m ) of the shear stress intensity of the groove part 3 is 3.40 N / mm 2 .

[0078] Also, since the average value of the mortar strength of the test specimens is 12.25 N / mm 2 , the relationship between the pile circumferential friction intensity (τ ft ) and the fixing part compressive strength (σ) within the fixing part 6 deeper than the α calculation position 9 (1.5D above the pile tip) is shown in Tables 10 and 11, and the maximum value of τ ft / σ is 0.120 and the minimum value is 0.091.

[0079]

Table 10

[0080]

Table 11

Explanation of Symbols

Claims

1. A pile body for an external excavation and foundation reinforcement method, which is installed in a straight-shaped pile hole, A cylindrical concrete pile body, The pile body comprises a plurality of grooves, each having a groove bottom smaller in diameter than the outer diameter of the pile body, provided on the outer circumferential surface of the portion embedded in the supporting layer of the pile body, These grooves have tapered sections at their corners, and all of them, corresponding to the pile diameter, are located within a length equal to the pile diameter from the tip of the pile body, which is embedded in the supporting layer. The long-term allowable shear stress of the concrete of the pile body is 1.65 N / mm² or higher, and the short-term allowable shear stress is 2.48 N / mm² or higher. A pile body for external excavation and foundation reinforcement construction, characterized by the above features.

2. All grooves are provided with the same shape and dimensions, and their number is set according to the pile diameter. The pile body for the external excavation and foundation reinforcement method according to claim 1.

3. The outer circumferential area of ​​the pile body between the grooves is larger than the outer circumferential area of ​​the grooves, and the ratio of their areas is 1.53 to 4.

11. The pile body for the external excavation and foundation reinforcement method according to claim 1.

4. The process of forming a straight-shaped pile hole, The process involves injecting a root-stabilizing liquid into the support layer portion of the pile hole, The process involves further injecting pile-peripheral fixing fluid into the pile hole, A step of sinking the pile body according to any one of claims 1 to 3 into a pile hole, The process involves solidifying the root reinforcement liquid and the pile perimeter fixing liquid to form a root reinforcement section and a pile perimeter fixing section on the outer circumference of the pile body, An external excavation and foundation reinforcement method characterized by having the following features.

5. The outer diameter of the base reinforcement section is between 1.33 and 1.35 times the pile diameter, and the height of the base reinforcement section below the tip of the pile body is 1.2 times the pile diameter. The external excavation and foundation reinforcement method described in feature 4.

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