Pile for outer excavated foot protection method and outer excavated foot protection 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 outside excavation and foot protection method and to an outside excavation and foot protection method. [Background technology]

[0002] Conventionally, the external excavation base reinforcement method involves excavating a straight pile hole of the same diameter over its entire length into the ground, sequentially injecting base reinforcement liquid and pile periphery fixing liquid into the pile hole, and then sinking a prefabricated pile to solidify the base reinforcement liquid and pile periphery fixing liquid, thereby forming a base reinforcement section and pile periphery fixing section around the pile (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2019-183510 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the case of the above-mentioned external excavation foot protection method, when a vertical load acts on the tip of the pile, the load is transmitted to the foot protection section through the pile by the adhesion forces from the inner and outer surfaces of the pile and the bearing pressure of the bottom end surface of the pile. The load is then transmitted to the foot protection section from the periphery and bottom surface of the pile in the foot protection section, and the pile and the foot protection section behave as one unit, and the load is transmitted to the supporting ground from the periphery and bottom surface of the foot protection section.

[0005] Therefore, in order to effectively transmit the vertical load to the supporting ground, it is desirable to improve the integrity between the pile tip and the base reinforcement portion.

[0006] The present invention has been developed in consideration of these points, and aims to provide a pile body for external excavation foot protection method and an external excavation foot protection method that can improve the integrity between the tip of the pile and the foot protection portion. [Means for solving the problem]

[0007] The pile body for external excavation and base protection method described in claim 1 is a pile body for external excavation and base protection method sunk into a straight-shaped pile hole, and comprises a cylindrical concrete pile body and a plurality of groove portions having groove bottoms with a diameter smaller than the outer diameter of the pile body provided on the outer surface of the part of the pile body that is embedded in the supporting layer, and these groove portions have tapered portions at the corners, and all of them, the number of which corresponds to the pile diameter, are within a length range equal to the pile diameter from the tip of the pile body that is embedded in the supporting layer.

[0008] The pile body for the external excavation and foot protection method described in claim 2 is a pile body for the external excavation and foot protection method described in claim 1, in which all groove portions are provided with the same shape and the same dimensions, and the number is set according to the pile diameter.

[0009] The pile body for the external excavation and foot protection method described in claim 3 is a pile body for the external excavation and foot protection method described in claim 1, in which the long-term allowable shear stress of the concrete in the pile body is 1.65 or more and the short-term allowable shear stress of the concrete is 2.48 or more.

[0010] The external excavation foot protection method described in claim 4 relates to a pile body for the external excavation foot protection method described in any one of claims 1 to 3, which comprises the steps of forming a straight-shaped pile hole, injecting a foot protection liquid into the supporting layer portion of the pile hole, further injecting a pile periphery fixing liquid into the pile hole, sinking a pile body described in any one of claims 1 to 3 into the pile hole, and solidifying the foot protection liquid and the pile periphery fixing liquid to form a foot protection portion and a pile periphery fixing portion on the outer periphery of the pile body.

[0011] The external excavation foot protection method described in claim 5 is the external excavation foot protection method described in claim 4, wherein the outer diameter of the foot protection portion is 1.33 to 1.35 times the pile diameter, and the height of the foot protection portion below the tip of the pile body is 1.2 times the pile diameter. Effect of the Invention

[0012] According to the present invention, it is possible to improve the integrity between the tip portion of the pile and the base protection portion. [Brief description of the drawings]

[0013] [Figure 1] FIG. 2 is a cross-sectional view of a pile body for an external excavation foot protection method according to one embodiment of the present invention during pile construction. [Diagram 2] FIG. 2 is an enlarged side view of a portion of the example of the pile body. [Diagram 3] FIG. 11 is an enlarged side view of a portion of another example of the pile body. [Figure 4] FIG. 2 is a side view showing the relationship between the outer peripheral area As1 of the grooves in the pile body and the outer peripheral area As2 of the pile main body sandwiched between the grooves. [Diagram 5] FIG. 2 is a cross-sectional view showing the relationship between an outer peripheral area As1 of the grooves in the pile body and an outer peripheral area As2 of the pile main body sandwiched between the grooves. [Figure 6] 4A to 4D are half-sectional views showing examples of the above pile bodies, where (a) shows an example of a pile diameter of φ300 mm, (b) shows an example of a pile diameter of φ350 mm, (c) shows an example of a pile diameter of φ400 mm, and (d) shows an example of a pile diameter of φ450 mm. [Figure 7] 4A and 4B are half-sectional views showing examples of the above pile bodies, where (a) shows an example of a pile diameter of φ500 mm, (b) shows an example of a pile diameter of φ600 mm, and (c) shows an example of a pile diameter of φ700 mm. [Figure 8] 4A and 4B are half-sectional views showing examples of the above pile bodies, where (a) shows an example of a pile diameter of φ800 mm, (b) shows an example of a pile diameter of φ900 mm, and (c) shows an example of a pile diameter of φ1000 mm. [Figure 9] 4A and 4B are half-sectional views showing examples of the above pile bodies, where (a) shows an example of a pile diameter of φ1100 mm, and (b) shows an example of a pile diameter of φ1200 mm. [Figure 10] 1A to 1E are explanatory cross-sectional views showing the above-mentioned outer excavation and foot protection method in the order of (a) to (e). [Figure 11] FIG. 13 is a cross-sectional view of test piece A having no groove. [Figure 12] FIG. 13 is a cross-sectional view of specimen B having two grooves with a groove depth of 3 mm. [Figure 13] FIG. 13 is a cross-sectional view of specimen C having two grooves with a groove depth of 7 mm. [Figure 14] FIG. 2 is an explanatory diagram showing a procedure for carrying out a load test on a test specimen. [Figure 15] This is a characteristic diagram of test results showing the relationship between the bond strength and pile head displacement of test specimen A-1. [Figure 16] This is a characteristic diagram of test results showing the relationship between the bond strength and pile head displacement of test specimen A-2. [Figure 17] This is a characteristic diagram of test results showing the relationship between the bond strength of test specimen B-1 and the pile head displacement. [Figure 18] This is a characteristic diagram of test results showing the relationship between the bond strength and pile head displacement of test specimen B-2. [Figure 19] This is a characteristic diagram of test results showing the relationship between the bond strength and pile head displacement of test specimen C-1. [Figure 20] This is a characteristic diagram of test results showing the relationship between the bond strength and pile head displacement of test specimen C-2. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0015] 1 shown in FIG. 1 is a pile body. The cross section of the pile body 1 is constructed by the outer excavation and enlarged footing construction method. The pile body 1 is a precast concrete pile, and is configured by forming a plurality of grooves (concave grooves) 3 having a groove bottom with a diameter smaller than the outer diameter of the pile body 2 on the outer surface of the bearing layer root part of the tip of the pile body 2 made of reinforced cylindrical concrete. A steel pipe shoe 4 is attached to the tip of the pile body 2 to temporarily reduce the friction force of the outer surface of the pile to facilitate the pile insertion construction. This pile body 1 is installed in a pile hole 5 having a straight shape over its entire length, and a footing part (footing bulb part) 6 formed at the tip of the pile and a pile periphery fixing part 7 formed around the pile constitute a foundation pile structure.

[0016] In this construction method, when a vertical load acts on the tip of the pile, the load is transmitted from the periphery and bottom of the pile in the base fixing section 6 to the base fixing section 6, and the pile body 2 and the base fixing section 6 behave as one unit, and the load is transmitted from the periphery and bottom of the base fixing section 6 to the supporting ground. The pile tip bearing capacity is the axial force (P) acting on the tip of the pile, and the bearing capacity of the ground at the lower end of the base fixing section 6 (P b) and the peripheral friction force of the foot protection part 6 (P fb ) and P = P b +P fb ...(Equation 1).

[0017] In this construction method, the frictional force of the base fixing portion 6 that is embedded in the supporting layer 8 underground is large due to the high ground strength. Therefore, by increasing the frictional force between the base fixing portion 6 and the pile body 1 and improving the integrity between the tip portion that is embedded in the supporting layer 8 of the pile body 1 and the base fixing portion 6, the frictional force between the supporting layer 8 and the base fixing portion 6 can be effectively utilized in the supporting force 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] The pile diameter D is preferably, for example, φ300mm to φ1200mm. The outer diameter Do of the base fixing portion 6 is set to 1.33 times the pile diameter D as standard, and is rounded up to the nearest 10mm. Table 1 shows examples of the relationship between the pile diameter D and the outer diameter Do of the base fixing portion 6 in this embodiment. In these examples, the outer diameter Do of the base fixing portion 6 is 1.33 to 1.35 times the pile diameter D. In the table, Di indicates the inner diameter of the pile, and H1 indicates the required height of the base fixing portion below the tip of the pile.

[0020] [Table 1]

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

[0022] The groove 3 is formed to improve the unity with the base fixing portion 6. In this embodiment, the groove 3 has a tapered portion 3a formed at each of the upper and lower corners as corners, which connect the groove bottom to the outer circumferential surface of the pile main body 2. By providing the tapered portion 3a, it is expected that the adhesion of soil and sand during pile insertion will be reduced, and by providing the tapered portion 3a, it is expected that the groove 3 will be less likely to be caught by underground obstacles during pile insertion, thereby preventing the groove 3 from being destroyed.

[0023] The grooves 3 are set at positions where the tip of the pile is embedded in the supporting layer 8, and are formed on the outer circumferential surface of the pile in a pile diameter D section from the tip of the pile. In this embodiment, the embedment length into the supporting layer 8 is equal to or greater than the pile diameter D. The intervals between the grooves 3 are set according to the pile diameter D so as to ensure the unity with the foot protection material (mortar) formed in each groove 3 against the shear force generated by the vertical load acting on the pile body 1, and are set at intervals of, for example, 150 mm to 300 mm. Furthermore, the shape of the grooves 3 is, for example, 3 mm in groove depth when the pile diameter D is small, and 7 mm in groove depth when the pile diameter D is large. As shown in FIG. 2, in this embodiment, in the case of the pile body 1 with a pile diameter of φ300 mm and φ350 mm, the groove depth is 3 mm, and as shown in FIG. 3, in the case of the pile body 1 with a pile diameter of φ400 mm to φ1200 mm, the groove depth is 7 mm. In addition, the groove width is 8 to 20 times the groove depth.

[0024] 1, the frictional force and the degree of friction that the groove portion 3 embedded in the support layer 8 can bear are determined. That is, the number of grooves 3 and the shear strength are set based on the frictional force and the degree of friction that the groove portion 3 embedded in the support layer 8 can bear.

[0025] The number of grooves 3 is set according to the pile diameter D based on the results of a shear test of the grooves 3. In this embodiment, in the case of a pile body 1 with a pile diameter of φ300mm to φ600mm, the number of grooves 3 is set to two, in the case of a pile body 1 with a pile diameter of φ700mm to φ900mm, the number of grooves 3 is set to three, and in the case of a pile body 1 with a pile diameter of φ1000mm to φ1200mm, the number of grooves 3 is set to four.

[0026] In addition, the shear strength of the groove 3 in this embodiment is set in consideration of the theoretical compressive strength of the foot protection portion 6. Here, the average N value of the ground near the tip of the pile and the pile tip blockage cross-sectional area (A p =π D 2 / 4, D is the pile diameter) and the axial force (=α N A p ) acts on the α calculation position 9, and the friction force (P fa ) and the damped axial force (= bearing capacity of the pile tip (P a )) acts on the tip of the pile. This damped axial force is transmitted to the foot protection section 6, and the foot protection section 6 below the tip of the pile is in a bearing state. Therefore, the bearing strength (F B ) The theoretical compressive strength of the foot protection section 6 required is calculated.

[0027] Bearing strength acting on the tip of the pile (F B ) is the bearing capacity acting on the tip of the pile (P a ) divided by the bearing area (A2) (=P a The bearing area is the pile tip closed cross-sectional area (A p ) is equal to the theoretical compressive strength (F C ) is based on the results of the bearing test. B ), bearing area (A2), bearing area (A k ), and the compressive strength of the foot reinforcement section 6. The results of the bearing test are used from "Chapter VI, 5. Basic tests carried out in existing performance evaluations, 5.3 Bearing test" conducted on March 22, 2006 in the Building Center of Japan's BCJ Basic Evaluation-FD0069-03 (MRXX method). In other words, the bearing area of ​​the test specimen was kept constant, and the bearing area was changed to examine the difference in bearing strength. As there was a tendency for the bearing strength to increase as the bearing area / bearing area ratio increased, a regression equation and a lower equation for the 95% confidence limit were obtained from the test results. The following equation obtained from this result is used.

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

[0029] The bearing capacity of the pile tip is calculated by subtracting the axial force acting on the pile tip (α calculation position 9) at the average N value (=60) of the ground near the pile tip from the bearing capacity coefficient α = 417, and the frictional force of the pile fixed to the base part 6. The bearing strength calculated from this value is 17.2 N / mm 2 The theoretical compressive strength of the foot protection section 6 is calculated from the above formula, and is 14.5 to 14.6 N / mm 2 It becomes.

[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" in August 2008, "Chapter 2, Tip Bearing Capacity, 2.5, Analysis of Tip Surface Bearing Capacity Focused on Pile Construction Method and Tip Shape, 2.5.2, Buried Piles (High Bearing Capacity Piles)" evaluates that "the α value at the tip of the base of an embedded pile is considered to be a reasonable value of 150 to 200, depending on the pile diameter." Based on the above formula 1, when an axial force equivalent to the bearing capacity coefficient α = 417 is applied, the bearing capacity coefficient α 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 (=P b / (N·A0), A0 is the cross-sectional area of ​​the foot protection section 6 (=π·Do 2 The frictional force (τ f ) 6.5N (from the panel discussion and keynote speech materials in the Structural Section (Foundation Structure) at the 2007 Architectural Institute of Japan Annual Meeting (Kyushu)) was adopted.

[0032] [Table 3]

[0033] Therefore, from this theoretical compressive strength, the set compressive strength of the foot protection section 6 is set to, for example, 14.60 N / mm 2 From the results of the shear test of the groove 3, the ratio of the shear strength of the groove 3 to the strength of the mortar specimen at 7 days is 0.26 to 0.29, so the shear strength of the groove 3 is 3.79 (= 14.60 × 0.26) N / mm 2 Let us assume that.

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

[0035] [Table 4]

[0036] As shown in Figs. 4 and 5, the outer peripheral area As2 of the pile body 2 sandwiched between the upper and lower grooves 3, 3 is larger than the outer peripheral area As1 of the groove 3. In other words, if the shear strength of the pile body concrete is considered to be on the safe side and is the same as the shear strength of the base protection material (mortar), in order for the pile body 2 to be safe against the axial force borne by the groove 3, if the outer peripheral area As2 of the pile body 2 is equal to or larger than the outer peripheral area As1 of the groove 3, the shear resistance area of ​​the pile body 2 becomes larger than the shear resistance area of ​​the base protection material in the groove 3, so that the pile body 2 will not be damaged by the shear stress τ. Table 5 shows examples of the pile diameter D, the outer peripheral area As1, the outer peripheral area As2, and their ratio, i.e., the area ratio, in this embodiment. In these examples, the area ratio is 1.53 to 4.11, and the pile body 1 will not be damaged by the shear force.

[0037] [Table 5]

[0038] Furthermore, when an ultimate vertical load acts on the pile body 1, the maximum shear force P acting on the concrete portion at the top of the groove 3 (the portion extending from the tapered portion 3a at the top of the groove 3 to the tapered portion 3a at the bottom of the groove 3 aligned with the top of the groove 3 (the range of As2 shown in Figures 4 and 5)) through the foot protection portion 6 filled in the groove 3 is max is the shear strength τ of the groove 3 u and the outer peripheral area As1 of the groove 3. At this time, the shear stress τ generated in the concrete part at the top of the groove 3 is max is the maximum shear force P max is divided by the outer peripheral area As2, so the shear strength τ of the groove portion 3 is u Divide by the area ratio between the outer perimeter area As2 and the outer perimeter area As1 (τ max = τ u This shear stress τ max is the maximum value when the ultimate vertical load acts, and even when the short-term allowable axial force acts, a shear stress exceeding this value will not occur in the pile body 1. Therefore, on the safe side, the concrete part at the top of the groove 3 is set to the required short-term allowable shear stress τ a2 Let this shear stress τ max Set to.

[0039] In addition, according to the Ministry of Land, Infrastructure, Transport and Tourism Notification No. 1113, Article 8, Paragraph 1, Item 5, the long-term allowable shear stress τ of the concrete part above the groove 3 is 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 concrete is the long-term allowable shear stress τ a1 is 1.65N / mm 2 The above is the short-term allowable shear stress τ a2 is 2.48N / mm 2 For example, the design strength (F) of the concrete used for the pile body 2 is set to 105 N / mm 2According to the Ministry of Land, Infrastructure, Transport and Tourism Notification No. 1113, Article 8, Paragraph 1, Item 5, the allowable shear stress of the concrete part above the groove 3 (long-term allowable shear stress τ c1 , short-term allowable shear stress τ c2 )teeth, τ c1 =1.2N / mm 2 τ c2 =1.8N / mm 2 Therefore, the long-term and short-term shear forces Q acting on the concrete part above the groove 3 and the allowable shear stress Q of the concrete part above the groove 3 are a Compared to (long term) Q=τ a1 As1 = 1.65 x 56549 = 93306 (N) Q a = τ c1 As2 = 1.2 x 86821 = 104185 (N) (short term) Q=τ a2 As1 = 2.48 x 56549 = 140242 (N) Q a = τ c2 As2=1.8×86821=156277(N) From Q a Therefore, by using concrete with the above allowable shear stress, the concrete portion in the upper part of the groove 3 will not be damaged.

[0041] ​Examples of the pile body 1 in this embodiment based on the above considerations are shown in Figs. 6 to 9. Fig. 6(a) shows an example of the pile body 1 with a pile diameter of φ300 mm, Fig. 6(b) shows an example of the pile body 1 with a pile diameter of φ350 mm, Fig. 6(c) shows an example of the pile body 1 with a pile diameter of φ400 mm, and Fig. 6(d) shows an example of the pile body 1 with a pile diameter of φ450 mm. Fig. 7(a) shows an example of the pile body 1 with a pile diameter of φ500 mm, Fig. 7(b) shows an example of the pile body 1 with a pile diameter of φ600 mm, and Fig. 7(c) shows an example of the pile body 1 with a pile diameter of φ700 mm. Fig. 8(a) shows an example of the pile body 1 with a pile diameter of φ800 mm, Fig. 8(b) shows an example of the pile body 1 with a pile diameter of φ900 mm, and Fig. 8(c) shows an example of the pile body 1 with a pile diameter of φ1000 mm. FIG. 9(a) shows an example of a pile body 1 having a pile diameter of φ1100 mm, and FIG. 9(b) shows an example of a pile body 1 having 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 is increased or decreased depending on the pile diameter D. The groove width of the grooves 3 is set to a constant value taking into consideration the shear strength of the foot protection material (mortar) in the grooves 3, and the groove depth of the grooves 3 is set to a constant value taking into consideration the covering amount up to the rebar in the pile body 2. In this way, by making the shape (dimensions) of the grooves 3 the same, the pile manufacturing (formwork) costs can be reduced.

[0043] Next, the effects of this embodiment will be described.

[0044] In the external excavation and foot protection method of this embodiment, first, as shown in Fig. 10(a), a straight-shaped pile hole 5 is excavated. At this time, the center of excavation by the auger (excavation and mixing device) 10 is aligned with the center of the pile, and the auger 10 is moved up and down as necessary while injecting water, etc., to excavate to the bottom of the foot protection of the supporting ground.

[0045] Next, as shown in Fig. 10(b), the root fixing liquid 11 is injected into the bearing layer 8 of the pile hole 5. For example, after half to the entire amount of the root fixing liquid 11 is injected at the lower end of the root fixing 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 1.7 times the pile diameter D, and after the entire amount of the root fixing liquid 11 is injected, the auger 10 is moved up and down repeatedly over the entire length of the root fixing section 6 as necessary.

[0046] 10(c), the pile hole 5 is further injected with the pile fixing fluid 12. At this time, for example, the auger 10 is raised while injecting the pile fixing fluid 12 from the lower end depth to the upper end depth of the injection range, and the auger 10 is repeatedly raised and lowered in the injection range one or more times. Then, the auger 10 is raised from the pile hole 5.

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

[0048] Then, the base fixing liquid 11 and the pile periphery fixing liquid 12 are solidified to form a base fixing portion 6 and a pile periphery fixing portion 7 on the outer periphery of the pile body 1 as shown in FIG. 10(e).

[0049] When a vertical load acts on the tip of the pile (α calculation position 9) of the pile body 1 sunk in this manner, as shown in Figure 1, the load is transmitted from the surrounding surface and bottom surface of the pile within the foot protection section 6 to the foot protection section 6, and the pile body 1 and the foot protection section 6 behave as a single unit, and the load is transmitted from the bottom surface of the foot protection section 6 to the supporting ground.

[0050] At this time, for the total cross-sectional area of ​​the bottom surface of the base fixing portion 6 to act effectively, the ratio (width ratio) between the outer diameter Do of the base fixing portion 6 and the pile diameter D and the ratio (height ratio) between the height H1 of the base fixing portion 6 and the pile diameter D are related. Table 6 shows examples of the width ratio and height ratio for an example of the pile body 1 of this embodiment.

[0051] [Table 6]

[0052] In this embodiment, the standard width ratio is 1.33, and the standard height ratio is 1.20, so that the total cross-sectional area of ​​the bottom surface of the foot fixing portion 6 can be effectively utilized.

[0053] In addition, the groove portion 3 ensures the integrity of the pile main body 2 and the base fixing portion 6.

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

[0055] By providing tapered portions 3a at the corners of the groove portion 3, it is possible to reduce the amount of soil adhering to the corners of the groove portion 3 when the pile is inserted, and it is also possible to reduce the resistance acting on the corners of the groove portion 3 from underground obstacles, thereby preventing destruction of the groove portion 3. Furthermore, by providing tapered portions 3a, it is possible to increase the bearing area when the pile is installed, which in turn reduces the bearing pressure, i.e., the stress load, and it is also possible to prevent damage to the groove portion 3 due to removal of the form during pile manufacturing, making it easier to remove the form.

[0056] Even if the pile diameter changes, the shape and dimensions of the grooves 3 can be left unchanged, and the number of grooves can be increased or decreased, allowing a common formwork for forming the grooves to be used, thereby reducing the pile manufacturing costs.

[0057] By setting the long-term allowable shear stress of the concrete of the pile body 2 to 1.65 or more and the short-term allowable shear stress to 2.48 or more, the concrete in the upper part of the groove portion 3 can be prevented from being damaged by shear force.

[0058] Since the outer peripheral area of ​​the pile body 2 between the groove portions 3, 3 is formed larger than the outer peripheral area of ​​the groove portion 2, the shear resistance area between the groove portions 3, 3 of the pile body 2 becomes larger than the shear resistance area of ​​the root fixing portion 6 formed within the groove portion 3, and shear failure between the groove portions 3, 3 of the pile body 2 can be prevented.

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

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

[0061] (1) Purpose of the study The load at the tip of the pile is transmitted to the base protection part 6 by adhesion forces from the inner and outer surfaces of the pile via the pile body 1, and by the bearing pressure at the bottom end of the pile. Here, in order to increase the adhesion strength between the base protection part 6 and the outer periphery of the pile, a groove part 3 is placed on the outer periphery of the pile tip, and the adhesion strength between the pile body 1 and the base protection part 6 is investigated.

[0062] (2) Test Overview (a) Details of the implementation The test specimen was based on a pile body 2 with an outer diameter of φ200 mm and a length of 300 mm, with a base protection section 6 formed on the outer periphery, and a push-out test was conducted. The test specimen had two grooves 3, with two groove 3 shapes set to depths of 3 mm and 7 mm, and a straight specimen without grooves 3 was also added, for a total of three types of concrete specimens.

[0063] (b) Type of test specimen Test specimens A, B, and C used to investigate the adhesion strength between the groove portion 3 and the foot protection portion 6 are shown in Table 7.

[0064] [Table 7]

[0065] (3) Creation of test specimen (a) Test specimen for bond strength investigation The cross-sectional shapes of the test specimens produced are mortar test specimens A-1 and A-2 having no grooves as shown in Figure 11, test specimens B-1 and B-2 having two grooves 3 with a groove depth of 3 mm as shown in Figure 12, and test specimens C-1 and C-2 having two grooves 3 with a groove depth of 7 mm as shown in Figure 13.

[0066] (b) Fabrication of test specimen Formwork for pile body 1; for centrifugal specimen (φ200mm~300mm) Foot protection section 6 formwork: PVC pipe (inner diameter φ286mm~250mm, thickness 16.2mm) Concrete mix for pile 1; compressive strength is σ u =105N / mm 2 Mixture of Mortar mix for foot protection section 6: Table 8

[0067] [Table 8]

[0068] The curing method was air curing. Three specimens (φ50mm~100mm) were made for strength investigation during production, and their strength was confirmed on the same day as the shear test.

[0069] (4) Test method The test method employed was a push-out test method in which a test piece was sandwiched between a pressure-receiving jig 15 and a pressure-applying jig 16 and pressurized, as shown in FIG.

[0070] Testing machine: 500t Amsla Displacement measuring device: High sensitivity displacement meter (stroke 50mm) Loading method: Continuous loading Measurement items: Load, pile head displacement (5) Summary of adhesion test results The test results are shown in Table 9. The relationship between the adhesive strength and the amount of displacement is shown in Figs. 15 to 20.

[0071] [Table 9]

[0072] (a) Specimens A-1 and A-2 without grooves break with linear displacement. Specimens B-1, B-2, C-1, and C-2 with grooves temporarily reduce the load after linear displacement, but as the displacement continues, the load increases again and reaches its maximum value.

[0073] (b) The bond strength of the outer surface of the pile to the base protection portion 6 is the average compressive strength of the mortar specimens A-1 and A-2 without the groove portion 3, which is 12.08 N / mm 2 In this case, the average adhesion strength is 0.77N / mm 2 The average compressive strength of the mortar specimens B-1 and B-2, which had a groove depth of 3 mm, was 12.33 N / mm 2 In this case, the average adhesion strength is 2.06N / mm2 The average compressive strength of the mortar specimens C-1 and C-2 with a groove depth of 7 mm was 12.35 N / mm 2 In this case, the average adhesion strength is 2.01N / mm 2 No significant difference in adhesion strength due to groove depth was confirmed.

[0074] (6) Friction force of the pile surface in the foot protection section 6 (τ ft ) and the compressive strength of the foot protection section (σ) From the results of the adhesion test, the friction force (τ ft ) and the compressive strength of the base protection section (σ).

[0075] The shear force of the groove 3 is calculated by subtracting the adhesive force of the adhesive surface area excluding the groove 3 from the test load. The calculation of the surface area excluding the groove 3 is done by adopting the average adhesive strength from the test results of the test piece A without the groove 3. Therefore, the shear stress intensity (τ m ) 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 of contact with the foot protection part 6 (mm), L1 is the length of the groove part 3 (mm), and τ st is the shear stress excluding the groove area (N / mm 2 ) The average shear stress τ of specimens A-1 and A-2 is st =0.77N / mm 2 It is.

[0077] The shear stress intensity borne by the groove 3 in the experimental results was 3.70 N / mm for specimens B-1 and B-2 with a groove depth of 3 mm. 2 , 3.20N / mm 2 , and for specimens C-1 and C-2 with a groove depth of 7 mm, the load was 3.72 N / mm 2 , 2.98N / mm 2 and the average shear stress intensity of the groove 3 (τm ) is 3.40N / mm 2 It becomes.

[0078] The average strength of the mortar specimens was 12.25N / mm 2 Therefore, the frictional force around the pile in the foot protection part 6 deeper than the α calculation position 9 (1.5D above the tip of the pile) (τ ft The relationship between the compressive strength of the foundation and the root protection section (σ) is shown in Tables 10 and 11. ft The maximum value of / σ was 0.120 and the minimum value was 0.091.

[0079] [Table 10]

[0080] [Table 11] [Explanation of symbols]

[0081] 1 Pile body 2 Pile body 3 Groove 3a Tapered section 5. Pilehole 6 Root protection section 7 Pile circumference fixing part 8 Support layer 11 Root hardening liquid 12 Pile circumference fixative D Pile diameter Do outer diameter

Claims

1. A pile body for an external excavation and foot protection method that is sunk into a straight-shaped pile hole, A cylindrical concrete pile body; A plurality of grooves having groove bottoms with a diameter smaller than the outer diameter of the pile body provided on the outer peripheral surface of the bearing layer embedded portion of the pile body, These grooves have tapered corners, and the number of grooves according to the pile diameter is determined based on the length of the pile from the tip of the pile body that is embedded in the supporting layer. A pile body for use in an external excavation and foot protection method.

2. All grooves are of the same shape and dimensions, and the number of grooves is set according to the pile diameter. A pile body for use in the external excavation and foot protection method according to claim 1.

3. The long-term allowable shear stress of the concrete in the pile body is 1.65 or more, and the short-term allowable shear stress is 2.48 or more. A pile body for use in the external excavation and foot protection method according to claim 1.

4. forming a straight-shaped pile hole; A step of injecting a root consolidation liquid into a supporting layer portion of the pile hole; Further injecting a pile periphery fixing liquid into the pile hole; A step of sinking the pile body according to any one of claims 1 to 3 into a pile hole; A step of solidifying the root fixing liquid and the pile periphery fixing liquid to form a root fixing portion and a pile periphery fixing portion on the outer periphery of the pile body; An external excavation and foot protection method characterized by comprising:

5. The outer diameter of the base protection part is 1.33 times or more and 1.35 times or less of the pile diameter, and the height of the base protection part below the tip of the pile body is 1.2 times the pile diameter.

5. The external excavation and foot protection method according to claim 4.

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