Pile foundations and their design methods

Abstract

To provide a pile foundation capable of properly evaluating bearing power of a pile, and to provide a design method of the same.SOLUTION: A pile foundation 10 includes a pile 8 formed by embedding a pile body 2 having at least one of a protrusion and a recess on a peripheral face in a pile hole 1 provided by excavating a ground via soil cement and hardening the soil cement to integrate it with the pile body 2. When assuming that a characteristic value related to a friction force reflecting a strength of the ground around the pile 8 is T, a length in a constant section where the pile 8 is in contact with the ground is L, geology of the ground is the same in the whole of the constant section, a peripheral length of the pile body 2 is ψ, an expansion ratio that is a ratio of an excavation diameter of the pile hole to a standard excavation diameter which is decided based on a pile diameter of the pile body 2 is ωs, and a target value of a surface friction to the pile hole 1 of the pile 8 in the constant section is Rf, Rf≤TLψωs is satisfied.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a pile foundation and a design method thereof. [Background technology]

[0002] A pile foundation usually includes multiple piles. For example, bored piles are used for the piles. Borehole piles can be constructed by mixing cement milk and excavated soil in a pile hole excavated in the ground to form soil cement, and then sinking prefabricated piles into this soil cement. When the soil cement hardens, it becomes integrated with the prefabricated piles to form the pile. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-98108 Summary of the Invention [Problem to be solved by the invention]

[0004] The bearing force that a pile receives from the ground consists of the tip bearing force acting from the ground at the bottom end of the pile and the skin friction force acting from the ground on the periphery of the pile. Skin friction force is thought to be affected by the excavation diameter of the pile hole. However, the effect of the excavation diameter on skin friction force has not been quantitatively and formally evaluated, and no evaluation method has been established. For this reason, conventional evaluation methods have not been considered appropriate for evaluating skin friction force.

[0005] An object of the present invention is to provide a pile foundation design method and pile foundation that can appropriately evaluate the bearing capacity that a pile receives from the ground. [Means for solving the problem]

[0006] A pile foundation according to one aspect of the present invention is a pile foundation including a pile having a pile body having at least one of a convex portion and a concave portion on its peripheral surface, which is embedded in a pile hole formed by excavating the ground via a hardening material, and the hardening material is hardened to be integrated with the pile body, wherein a characteristic value relating to the frictional force reflecting the strength of the ground around the pile is defined as T, the length of a certain section where the pile is in contact with the ground is defined as L, the ground in the certain section has the same geology, the perimeter of the pile body is defined as ψ, and an expansion ratio which is the ratio of the excavation diameter of the pile hole to the standard excavation diameter determined based on the pile diameter of the pile body is defined as ω. s If the target value of the surface friction force of the pile against the pile hole in a certain section is Rf, then Rf ≦ TLψω s Meet the following.

[0007] According to this aspect of the pile foundation, the expansion ratio ω, which is the ratio of the excavation diameter of the pile hole to the standard excavation diameter determined based on the pile diameter of the pile body s By adding this to the evaluation criteria for the skin friction force of the pile, the bearing capacity that the pile receives from the ground can be appropriately evaluated.

[0008] A design method for a pile foundation according to another aspect is a design method for a pile foundation including a pile having a pile body having at least one of a convex portion and a concave portion on its peripheral surface, which is embedded in a pile hole formed by excavating the ground via a hardening material, and the hardening material is hardened to be integrated with the pile body, the design method including the method defining a characteristic value related to frictional force reflecting the strength of the ground around the pile as T, a length of a certain section where the pile is in contact with the ground as L, the ground in the certain section has the same geology, a perimeter of the pile body as ψ, and an expansion ratio which is a ratio of the excavation diameter of the pile hole to a standard excavation diameter determined based on the pile diameter of the pile body as ω, s If the target value of the surface friction force of the pile against the pile hole in a certain section is Rf, then Rf ≦ TLψω s The pile foundation is designed to satisfy the following.

[0009] According to this aspect of the pile foundation design method, the expansion ratio ω, which is the ratio of the excavation diameter of the pile hole to the standard excavation diameter determined based on the pile diameter of the pile body s By adding this to the evaluation criteria for the skin friction force of the pile, the bearing capacity that the pile receives from the ground can be appropriately evaluated.

[0010] The characteristic value T varies depending on the geology of the ground and the type of hardening material as follows: The ground in a certain section is sandy or gravelly ground, and the average N value of the sandy or gravelly ground in that section is N s If T is the characteristic value and N is the average value, s The relationship is T=A+B×N s If the hardener does not contain an expanding agent, A is 25≦A≦35, and B is 4.5≦B≦5.5. If the hardener contains an expanding agent, A is 0, and B is 9.0≦B≦10.0.

[0011] The ground in a certain section is clayey ground, and the average unconfined compressive strength of the clayey ground in that section is q u If so, the characteristic value T and the average value of the unconfined compressive strength q u The relationship is T=A+B×q u When the hardener does not contain an expanding agent, A is 15≦A≦25 and B is 0.5≦B≦1.0. When the hardener contains an expanding agent, A is 0 and B is 0.5≦B≦1.5. [Effects of the Invention]

[0012] According to the present invention, it is possible to provide a pile foundation design method and a pile foundation that can appropriately evaluate the bearing capacity that a pile receives from the ground. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing a pile foundation according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram for explaining the peripheral friction force of a pile included in the pile foundation according to the embodiment. [Figure 3] FIG. 3 is a diagram for explaining the design method of the pile foundation according to the embodiment. [Figure 4] Figure 4 shows the results of a load test in which a standard nodular pile was installed in a pile hole in sandy or gravelly ground, plotting the data as a relationship between the average N value and the skin friction resistance stress, along with the data for the calculation formula. [Figure 5] Figure 5 shows the results of a load test in which a circumferentially reinforced pile using nodular piles was installed in a pile hole in sandy or gravelly ground, plotting the data as a relationship between the average N value and the circumferential friction resistance stress, along with the data for the calculation formula. [Figure 6] Figure 6 shows the results of a load test in which a standard pile using a nodular pile was installed in a pile hole in clayey ground, plotting the data as the relationship between the average uniaxial compressive strength qu and the skin friction resistance stress, along with data for the calculation formula. [Figure 7] Figure 7 shows the results of a load test in which a circumferentially reinforced pile using nodular piles was installed in a pile hole in clayey ground, and plotted as the relationship between the average uniaxial compressive strength qu and the circumferential friction resistance stress, along with data for the calculation formula. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments will be described with reference to the drawings. As shown in FIG. 1 , the pile foundation 10 of a building 100 has, for example, a plurality of piles 8 set in a plurality of pile holes 1 set in the ground G. The type, length, diameter, number, layout, etc. of the piles 8 are determined depending on the weight and shape of the building 100, the condition of the ground G, etc. The pile foundation 10 does not necessarily have to have a plurality of piles 8, but only needs to have at least one pile 8.

[0015] The pile 8 has a pile body 2 formed by, for example, two or more precast piles connected in the axial direction. The pile body 2 may also be formed by a single precast pile. Examples of precast piles include concrete piles and steel pipe piles. The pile body 2 of the pile 8 included in the pile foundation 10 of this embodiment has a structure in which two hollow concrete piles are connected together.

[0016] The pile body 2 has a structure in which a nodular pile 14 is connected to the lower end of a cylindrical straight pile 12, as in this embodiment, or a structure in which two nodular piles 14 are connected one above the other. The nodular pile 14 has a shaft portion with approximately the same diameter as the pile diameter of the straight pile 12, and is integrally provided with a plurality of annular nodular portions 16 spaced apart in the longitudinal direction on the circumferential surface of the shaft portion.

[0017] In this embodiment, the pile body 2 includes at least one nodular pile 14, but the pile body 2 may also be formed using other prefabricated piles having at least one of a convex portion and a concave portion on the circumferential surface. Examples of such other prefabricated piles include those with grooves on the circumferential surface and those with checkered steel plates wrapped around the circumferential surface.

[0018] The pile main body 2 does not necessarily have to include the straight pile 12, and may be, for example, a combination of multiple types of nodular piles, or may be a prefabricated pile having the above-described convex or concave portions on its circumferential surface instead of the nodular pile. Alternatively, the pile main body 2 may be formed by connecting a nodular pile and another prefabricated pile having the above-described convex or concave portions on its circumferential surface. In any case, the pile main body 2 is sufficient as long as at least one prefabricated pile has at least one convex or concave portion on its circumferential surface.

[0019] The length of the pile body 2 is desirably set to a length that allows the tip of the pile body 2 to reach the bearing layer 3 of the ground G. For this reason, it is desirably set so that the pile hole 1 is also formed to a depth that allows the tip to reach the bearing layer 3. However, the length of the pile body 2 does not necessarily have to be set to a length that allows the tip to reach the bearing layer 3.

[0020] The length of the pile main body 2 can be adjusted by selecting the length and number of precast piles to be connected. The pile main body 2 may have a structure in which, for example, three or more precast piles are connected. The type and diameter of the precast piles that make up the pile main body 2 may be appropriately selected based on the bearing capacity required of the pile main body 2.

[0021] In addition to the pile main body 2 described above, the pile 8 has a base fixing portion 4 provided to surround the tip of the pile main body 2, and a pile peripheral portion 6 provided to surround the peripheral surface of the pile main body 2. The base fixing portion 4 and the pile peripheral portion 6 are formed by providing soil cement (hardening material) between the inner wall surface of the pile hole 1 and the outer peripheral surface of the pile main body 2 and allowing the soil cement to harden. When the soil cement provided in the base fixing portion 4 and the pile peripheral portion 6 hardens, the base fixing portion 4 and the pile peripheral portion 6 are integrated with the concrete pile main body 2 to form the pile 8. The pile peripheral portion 6 is provided continuously above the base fixing portion 4.

[0022] Soil cement is formed by excavating the ground G to form a pile hole 1, leaving a predetermined amount of excavated soil in the pile hole 1, injecting a predetermined amount of cement milk into the pile hole 1, and stirring and mixing the cement milk and excavated soil. The pile body 2 is then sunk into the soil cement in the pile hole 1, and the soil cement hardens and becomes integrated with the pile body 2, thereby forming the pile 8. Note that the hardening material to be placed between the pile body 2 and the pile hole 1 can also be soil cement, which is made by adding additives such as bentonite or a retarder to cement milk and stirring and mixing it with the excavated soil.

[0023] The base fixing portion 4 is provided on the bottom side of the pile hole 1 so as to surround the tip of the pile main body 2, mainly to increase the tip bearing force that the ground G (the bearing layer 3 of the ground G when the tip of the pile main body 2 reaches the bearing layer 3) supports at the tip (lower end in the figure) of the pile main body 2. The pile peripheral portion 6 is provided between the peripheral surface of the pile main body 2 and the inner wall surface of the pile hole 1, mainly to increase the peripheral friction force that the peripheral surface of the pile main body 2 receives from the ground G.

[0024] The pile hole 1 has a pile-periphery excavation section 22 with an inner diameter larger than the outer diameter of the pile body 2, and an enlarged excavation section 24 that partially enlarges the diameter of the lower end side of the pile-periphery excavation section 22. A part of the shaft hole excavated in the ground G by a specified excavator becomes the pile-periphery excavation section 22 as it is. The pile hole 1 can also be a hole of the same diameter as the pile-periphery excavation section 22 over its entire length without providing the enlarged excavation section 24. The enlarged excavation section 24 has a length shorter than half the entire length of the pile hole 1, for example, and is provided on the bottom side of the pile hole 1.

[0025] The outer diameter of the pile body 2 is the diameter of its cross section in the case of a straight pile 12, and is the diameter of the node 16 in the case of a nodular pile 14. In the claims, the outer diameter of a pile body having at least one of a convex portion and a concave portion on its peripheral surface is the diameter of the portion where the outer diameter of the pile body is maximum. In other words, in this embodiment, the outer diameter of the pile body 2 is the diameter of the node 16 of the nodular pile 14.

[0026] The tip of the pile main body 2 is placed within the enlarged excavation section 24. The foot protection section 4 is provided in the enlarged excavation section 24. In other words, the enlarged excavation section 24 is formed to have a length at least equal to or greater than the length of the foot protection section 4. The pile peripheral surface section 6 may be provided across the pile peripheral excavation section 22 and the enlarged excavation section 24, as in this embodiment. For example, the foot protection section 4 may be provided over the entire length of the enlarged excavation section 24, and the pile peripheral surface section 6 may be provided only in the pile peripheral excavation section 22.

[0027] The bearing force that the pile 8 of the above structure receives from the ground G includes the tip bearing force acting from the ground G on the tip of the pile 8 and the circumferential friction force acting from the ground G on the circumferential surface of the pile 8. In other words, the bearing force that the pile 8 receives from the ground G is the sum of the tip bearing force and the circumferential friction force. In designing the pile foundation 10, the allowable bearing force of the pile 8 is determined to be the smaller of the bearing force that each pile 8 of the pile foundation 10 receives from the ground G or the material strength of the pile body 2 of the pile 8 itself.

[0028] For example, if an attempt is made to increase the tip bearing capacity of the pile 8 by expanding only the enlarged excavation section 24 without changing the diameter of the pile periphery excavation section 22 in order to increase the allowable bearing capacity of the pile 8, the difference between the diameter of the pile periphery excavation section 22 and the diameter of the enlarged excavation section 24 in the pile hole 1 will become large. In this case, it becomes more necessary to use a hydraulic excavation device that can widely open the movable wings for excavating the enlarged excavation section 24. If a hydraulic excavation device is used, the device configuration will be larger than that of a mechanical excavation device, and the construction costs of the pile foundation 10 will be higher.

[0029] Furthermore, if only the enlarged excavation section 24 is enlarged as described above, the inner diameter of the pile circumferential excavation section 22 will be only slightly larger than the outer diameter of the pile body 2, making it difficult to insert the pile body 2 into the pile hole 1. This increases the possibility that the pile body 2 will come into contact with the inner wall surface of the pile hole 1, causing damage to the inner wall surface of the pile hole 1. In other words, in this case, the pile body 2 must be inserted carefully and slowly into the pile hole 1, making construction of the pile foundation 10 difficult.

[0030] For this reason, it is considered important to appropriately evaluate the peripheral friction force of the pile 8 so that the inner diameter of the pile peripheral excavation portion 22 can be increased to reduce the difference with the inner diameter of the enlarged excavation portion 24. Therefore, in this embodiment, the enlargement ratio ω s By adjusting the above, the peripheral friction force of the pile 8 is increased, and the bearing capacity that the pile 8 receives from the ground G is increased.

[0031] That is, according to the design method of this embodiment, the expansion ratio ω s can be set to an appropriate value, the difference in diameter between the pile surrounding excavation section 22 and the enlarged excavation section 24 can be reduced, the degree of freedom in designing the pile foundation 10 can be increased, and the above-mentioned conventional problems can be solved.

[0032] A design method for the pile foundation 10 according to this embodiment will be described below with reference to Figures 2 to 7. Note that the design method of this embodiment is applied to the nodular piles 14 of each pile 8 of the pile foundation 10, but not to the straight piles 12. The piles 8 described up to this point include those having a structure in which straight piles 12 are arranged in the pile-circumferential excavation portion 22 of the pile hole 1, but the piles 8 in the following description will be those having a structure in which nodular piles 14 are arranged in the pile-circumferential excavation portion 22.

[0033] First, as shown in Figure 2, a certain section of length L (m) where the pile 8 contacts the ground G is defined. The certain section is the section where the portion of the pile 8, including the nodular pile 14, contacts the ground G, and the length L can be set arbitrarily within the length of the nodular pile 14. Furthermore, the ground G in the certain section where the portion of the pile 8, including the nodular pile 14, contacts is assumed to be of the same geology, and the certain section does not include multiple types of geological layers. In other words, the certain section is set within a range of the same geology where the geology of the ground G that contacts the portion of the pile 8, including the pile body 2, which has at least one of a convex portion and a concave portion on its circumferential surface, is continuous in the axial direction. Furthermore, even if the geology is the same, the soil type may differ depending on the particle size distribution of the soil particles that make up the ground G. Therefore, when determining the certain section, the division by soil type name is also taken into consideration.

[0034] The pile foundation 10 is then designed so that the peripheral friction force of the pile 8 in this certain section exceeds a predetermined value. The predetermined value here refers to the design value of the peripheral friction force that the portion of the pile 8 in the certain section receives from the ground G, out of the load that the pile foundation 10 receives from the building 100 (Fig. 1), and is the target value of the peripheral friction force of the pile 8 when designing the pile foundation 10.

[0035] The characteristic value of the friction force reflecting the strength of the ground G around the pile 8 in the above-mentioned certain section is T, the perimeter of the node 16 of the node pile 14 existing in the certain section is ψ, and the diameter D of the node 16 of the node pile 14 existing in the certain section is os (i.e., the pile diameter of the pile body 2) ss Diameter D of pile hole 1 es The ratio (D es / D ss ) is the expansion ratio ω s If the target value of the surface friction force that the pile 8 in a certain section receives from the ground G is Rf, Rf≦TLψω s ···(1) The pile foundation 10 is designed to satisfy the following.

[0036] In addition, the perimeter ψ of the pile body in the claims is the perimeter of the portion where the outer diameter of the pile body in a certain section is maximum, and the pile diameter in the claims is the diameter of the portion where the outer diameter of the pile body in a certain section is maximum. In this embodiment, the perimeter ψ of the pile body 2 is the perimeter of the node 16, and the pile diameter of the pile body 2 is the diameter of the node 16. In addition, the pile diameter D of the pile body 2 os Standard reference drilling diameter D determined based on ss is the pile diameter D os It should be about +50mm.

[0037] That is, according to the design method of this embodiment, the expansion ratio ω of the pile peripheral surface portion 6 s By adjusting the expansion ratio ω, the peripheral friction force of the pile 8 existing in a certain section of the length L can be made larger than the target value Rf. sBy changing the value of the friction coefficient, it is possible to control the peripheral friction force acting on the pile 8 from the ground G. Therefore, according to this embodiment, the peripheral friction force of the pile 8 can be appropriately evaluated, and the bearing force that the pile 8 receives from the ground G can be appropriately evaluated.

[0038] Furthermore, according to this embodiment, the difference in diameter between the pile-periphery excavation section 22 of the pile hole 1 in which the pile foundation 10 is constructed and the enlarged excavation section 24 can be reduced (or in some cases eliminated), making it possible to use a mechanical excavation device for construction. This reduces construction costs and makes construction easier.

[0039] In the above description of the design method, the diameter D of the node 16 os Standard excavation diameter D added 50 mm to ss Diameter D of pile hole 1 es The ratio (D es / D ss ) is the expansion ratio ω of the pile peripheral surface 6 s However, the standard excavation diameter D ss is the diameter D of the node 16 os It is sufficient if it is several tens of mm larger than the above, and it is not limited to 50 mm.

[0040] As shown in Figure 3, the characteristic value T of the above-mentioned formula (1) varies depending on the geology of the ground G (sandy / gravel ground, clayey ground) and the material of the pile peripheral portion 6 (standard type, peripheral reinforced type).

[0041] The ground G around the pile hole 1 in a certain section of length L is sandy and gravelly ground, and its average N value is N s Then, the characteristic value T in equation (1) is T=A+BN s ···(2) It can be expressed as:

[0042] The characteristic value T is the distance between the ground G and the pile hole 1 in the above-mentioned certain section. Circumferential friction force is the value obtained by dividing by the perimeter ψ of the pile body 2 × the fixed section L. Circumferential friction forcevaries depending on the strength of the ground G. The characteristic value T can be calculated from Ns (the average N value of the sandy / gravelly ground in a certain section L) by using coefficients A and B of the linear function. Coefficients A and B can be determined from the relationship between Ns and T that has been confirmed through experiments, etc. Coefficient A corresponds to the Y-intercept of the linear function in equation (2), and coefficient B corresponds to the gradient of the linear function in equation (2).

[0043] The experimental data in Figure 4 plots the results of multiple load tests on standard piles 8 that were actually installed in pile holes 1 in sandy and gravelly ground using nodular piles 14. The results show the relationship between the average N value of the ground and the actual N value acting on the piles 8. Surface friction resistance stress (friction resistance force per unit area) The standard pile 8 referred to here is a pile whose peripheral portion 6 is constructed from soil cement that does not contain anhydrous gypsum (expansive material).

[0044] The solid line in Figure 4 shows a calculation formula, which is an example of formula (2), and is based on the calculated value obtained by appropriately setting coefficients A and B within the range that satisfies the calculated value≦actually measured value. The calculation formula shown by the solid line in Figure 4 is T=30+5.5N s Looking at Figure 4, we can see that all the measured values ​​exceed the calculation formula. In other words, when a standard pile 8 is installed in sandy or gravelly ground, the characteristic value T is (30 + 5.5N s ) and proves that the following equation (1-1) holds true. Rf≦(30+5.5N s )Lψω s ···(1-1)

[0045] 4 indicates the calculated value input into equation (2) when coefficient A is set to the maximum value (A=42) of the above range and coefficient B is set to the minimum value (B=0), and the two-dot chain line in Fig. 4 indicates the calculated value input into equation (2) when coefficient A is set to the minimum value (A=0) and coefficient B is set to the maximum value (B=6.8) of the above range. In other words, it can be said that the maximum value of coefficient A in equation (2) based on the actual measured values ​​in Fig. 4 is 42, and the maximum value of coefficient B is 6.8.

[0046] Furthermore, there are countless combinations of coefficients A and B within the above ranges. However, when determining the appropriate values ​​for coefficients A and B from the actual measured values ​​in Figure 4, it can be said that coefficient A is preferably in the range of 25≦A≦35, and coefficient B is preferably in the range of 4.5≦B≦5.5.

[0047] The experimental data in Figure 5 plots the results of multiple load tests on the circumferential reinforced piles 8 that were actually constructed in pile holes 1 in sandy and gravelly ground using nodular piles 14. The results show the relationship between the average N value of the ground and the actual N value acting on the piles 8. Surface friction resistance stress The periphery reinforced pile 8 referred to here is a pile whose periphery 6 is constructed from soil cement containing anhydrous gypsum (expansive material).

[0048] The solid line in Figure 5 shows a calculation formula, which is an example of formula (2), and is based on the calculated value obtained by appropriately setting coefficients A and B within the range that satisfies the calculated value≦actually measured value. The calculation formula shown by the solid line in Figure 5 is T=9.5N s Looking at Figure 5, it can be seen that all the measured values ​​exceed the calculation formula. In other words, when a reinforced pile 8 is installed in sandy or gravelly ground, the characteristic value T is (9.5N s ) and proves that the following equation (1-2) holds true. Rf≦(9.5N s )Lψω s (1-2)

[0049] 5 indicates the calculated value input into equation (2) when coefficient A is set to the maximum value (A=48) of the above range and coefficient B is set to the minimum value (B=0), and the two-dot chain line in Fig. 5 indicates the calculated value input into equation (2) when coefficient A is set to the minimum value (A=0) and coefficient B is set to the maximum value (B=9.8) of the above range. In other words, it can be said that the maximum value of coefficient A in equation (2) based on the actual measured values ​​in Fig. 5 is 48, and the maximum value of coefficient B is 9.8.

[0050] Furthermore, there are an infinite number of combinations of coefficients A and B within the above ranges. However, when determining the appropriate values ​​for coefficients A and B from the actual measured values ​​in Figure 5, it can be said that coefficient A is preferably 0, and coefficient B is preferably 9.0≦B≦10.0.

[0051] The ground G around the pile hole 1 in a certain section of length L is clayey ground, and its average unconfined compressive strength is q u Then, the characteristic value T in equation (1) is T=A+Bq u ···(3) It can be expressed as:

[0052] The characteristic value T is the distance between the ground G and the pile hole 1 in the above-mentioned certain section. Circumferential friction force is the value obtained by dividing by the perimeter ψ of the pile body 2 × the fixed section L. The characteristic value T is calculated by using the coefficients A and B of the linear function. u (average value of unconfined compressive strength of the clayey ground in a certain section L). Coefficients A and B are determined by experiments etc. u and T, where coefficient A corresponds to the Y intercept of the linear function of equation (3), and coefficient B corresponds to the gradient of the linear function of equation (3).

[0053] The experimental data in Figure 6 plots the results of multiple load tests on standard piles 8 that were actually installed in pile holes 1 in clayey ground using nodular piles 14. The average uniaxial compressive strength of the ground and the actual strength acting on the piles 8 are shown. Surface friction resistance stress This shows the relationship between

[0054] The solid line in Figure 6 shows a calculation formula, which is an example of formula (3), and is based on the calculated value obtained by appropriately setting coefficients A and B within the range that satisfies the calculated value≦actually measured value. The calculation formula shown by the solid line in Figure 6 is T=20+0.5q u Looking at Figure 6, we can see that all the measured values ​​exceed the calculation formula. In other words, when a standard pile 8 is installed in clayey ground, the characteristic value T is (20 + 0.5q u) holds true. Rf≦(20+0.5q u )Lψω s (1-3)

[0055] 6 indicates the calculated value input into equation (3) when coefficient A is set to the maximum value (A=37) of the above range and coefficient B is set to the minimum value (B=0), and the two-dot chain line in Fig. 6 indicates the calculated value input into equation (3) when coefficient A is set to the minimum value (A=0) and coefficient B is set to the maximum value (B=0.66) of the above range. In other words, it can be said that the maximum value of coefficient A in equation (3) based on the actual measured values ​​in Fig. 6 is 37, and the maximum value of coefficient B is 0.66.

[0056] Furthermore, there are countless combinations of coefficients A and B within the above ranges. However, when determining the appropriate values ​​for coefficients A and B from the actual measurement values ​​in Figure 6, it can be said that coefficient A is preferably in the range of 15≦A≦25, and coefficient B is preferably in the range of 0.5≦B≦1.0.

[0057] The experimental data in Figure 7 plots the results of multiple load tests on the circumferential reinforced piles 8 that were actually constructed in pile holes 1 in clayey ground using nodular piles 14. The average uniaxial compressive strength of the ground and the actual strength acting on the piles 8 are shown. Surface friction resistance stress This shows the relationship between

[0058] The solid line in Figure 7 shows a calculation formula, which is an example of formula (3), and is based on the calculated value obtained by appropriately setting coefficients A and B within the range that satisfies the calculated value≦actually measured value. The calculation formula shown by the solid line in Figure 7 is T=q u From Figure 7, it can be seen that all the measured values ​​exceed the calculation formula. In other words, when a reinforced pile foundation 10 is constructed on clayey ground, the characteristic value T is (q u ) holds true. Rf≦(q u )Lψω s (1-4)

[0059] 7 shows the calculated value input into equation (3) when coefficient A is set to the maximum value (A=37) of the above range and coefficient B is set to the minimum value (B=0), and the two-dot chain line in Fig. 7 shows the calculated value input into equation (3) when coefficient A is set to the minimum value (A=0) and coefficient B is set to the maximum value (B=1.0) of the above range. In other words, it can be said that the maximum value of coefficient A in equation (3) based on the actual measurement values ​​in Fig. 7 is 37, and the maximum value of coefficient B is 1.0.

[0060] Furthermore, there are an infinite number of combinations of coefficients A and B within the above ranges. However, when determining the appropriate values ​​for coefficients A and B from the actual measurement values ​​in Fig. 7, it can be said that coefficient A is preferably 0, and coefficient B is preferably 0.5≦B≦1.5.

[0061] As described above, according to this embodiment, the expansion ratio ω of the pile peripheral surface portion 6 of each pile 8 of the pile foundation 10 s Therefore, the bearing force that the pile foundation 10 receives from the ground G can be made larger than the allowable bearing force without increasing the tip bearing force that the pile foundation 10 receives from the ground G more than necessary.

[0062] Furthermore, according to this embodiment, the difference in diameter between the pile-periphery excavation portion 22 of the pile hole 1 for constructing each pile 8 of the pile foundation 10 and the enlarged excavation portion 24 can be reduced, making it possible to excavate the pile hole 1 using a mechanical excavator. This reduces the construction cost of the pile foundation 10 and makes construction easier.

[0063] Furthermore, according to this embodiment, for example, when excavating the pile hole 1, the diameter of the pile periphery excavation portion 22 (i.e., the expansion ratio ω s ) is determined first, and the shortfall in the bearing capacity of the pile 8 relative to the allowable bearing capacity is calculated, and the shortfall can be made up by adjusting the diameter of the enlarged excavation section 24. This increases the degree of freedom in designing the pile foundation 10, making it easier to design the pile foundation 10.

[0064] The present invention is not limited to the above-described embodiments, and various modifications can be made in the implementation stage without departing from the spirit of the invention. Furthermore, the above-described embodiments include various inventions, and various inventions can be extracted by selecting and combining the multiple constituent elements disclosed. For example, if the problem can be solved and the desired effect can be obtained even if some constituent elements are deleted from all the constituent elements shown in the embodiments, the configuration from which these constituent elements are deleted can be extracted as an invention. The inventions described in the claims of the present application as originally filed are as follows: [1] A pile foundation including a pile having a pile body having at least one of a convex portion and a concave portion on the peripheral surface, which is embedded in a pile hole formed by excavating the ground via a hardening material, and the hardening material is hardened to be integrated with the pile body, Let T be the characteristic value related to the frictional force that reflects the strength of the ground around the pile, L be the length of a certain section where the pile contacts the ground, the ground in the certain section has the same geology, ψ be the circumference of the pile body, and ω be the expansion ratio, which is the ratio of the excavation diameter of the pile hole to the standard excavation diameter determined based on the pile diameter of the pile body. s and the pile holes of the piles in the certain section are If the target value of the peripheral friction force is Rf, Rf≦TLψω s Pile foundation that meets the above requirements. [2] The ground in the certain section is sandy or gravelly ground, and the average N value of the sandy or gravelly ground in the certain section is N s and the characteristic value T and the average N value N s The relationship between T=A+B×N s Pile foundations that meet the following criteria [1]. [3] When the hardener does not contain an expansion agent, wherein A is 25≦A≦35; The B is 4.5≦B≦5.5. [2] Pile foundation. [4] When the hardening material contains an expansion material, A is 0, The B is 9.0≦B≦10.0. [2] Pile foundation. [5] The ground in the certain section is clayey ground, and the average value of the uniaxial compressive strength of the clayey ground in the certain section is q u and the characteristic value T and the average value q of the unconfined compressive strength u Relationship with but, T=A+B×q u Pile foundations that meet the following criteria [1]. [6] When the hardener does not contain an expansion agent, wherein A is 15≦A≦25; The B is 0.5≦B≦1.0. [5] Pile foundation. [7] When the hardening material contains an expansion material, A is 0, The B is 0.5≦B≦1.5. [5] Pile foundation. [8] A method for designing a pile foundation including a pile in which a pile body having at least one of a convex portion and a concave portion on its peripheral surface is embedded in a pile hole formed by excavating the ground via a hardening material, and the hardening material is hardened to be integrated with the pile body, Let T be the characteristic value related to the frictional force that reflects the strength of the ground around the pile, L be the length of a certain section where the pile contacts the ground, the ground in the certain section has the same geology, ψ be the circumference of the pile body, and ω be the expansion ratio, which is the ratio of the excavation diameter of the pile hole to the standard excavation diameter determined based on the pile diameter of the pile body. s and the pile holes of the piles in the certain section are If the target value of the peripheral friction force is Rf, Rf≦TLψω s A method for designing the pile foundation to satisfy the above. [9] The ground in the certain section is sandy or gravelly ground, and the average N value of the sandy or gravelly ground in the certain section is N s and the characteristic value T and the average N value N s The relationship between T=A+B×N s The pile foundation design method [8] satisfies the following.

[10] When the hardener does not contain an expansion agent, wherein A is 25≦A≦35; The B is 4.5≦B≦5.5. [9] Pile foundation design method.

[11] When the hardening material contains an expansion material, A is 0, The B is 9.0≦B≦10.0. [9] Pile foundation design method.

[12] The ground in the certain section is clayey ground, and the average value of the uniaxial compressive strength of the clayey ground in the certain section is qu and the characteristic value T and the average value q of the unconfined compressive strength u Relationship with but, T=A+B×q u The pile foundation design method [8] satisfies the following.

[13] When the hardener does not contain an expansion agent, wherein A is 15≦A≦25; The B is 0.5≦B≦1.0.

[12] Pile foundation design method.

[14] When the hardening material contains an expansion material, A is 0, The B is 0.5≦B≦1.5.

[12] Pile foundation design method. [Explanation of symbols]

[0065] 1...pile hole, 2...pile body, 3...supporting layer, 4...foot reinforcement section, 6...pile peripheral section, 8...pile, 10...pile foundation, 12...straight pile, 14...nodal pile, 16...nodal section, 22...pile peripheral excavation section, 24...expanded excavation section, 100...building, G...ground.

Claims

1. A pile foundation including a pile having a pile body having at least one of a convex portion and a concave portion on the peripheral surface, which is embedded in a pile hole formed by excavating the ground via a hardening material, and the hardening material is hardened to be integrated with the pile body, Let T be a characteristic value related to the frictional force that reflects the strength of the ground around the pile, L be the length of a certain section where the pile contacts the ground, the ground in the certain section has the same geology, ψ be the circumference of the pile body, and ω be the expansion ratio, which is the ratio of the excavation diameter of the pile hole to the standard excavation diameter determined based on the pile diameter of the pile body. ｓ When the target value of the peripheral friction force of the pile against the pile hole in the certain section is Rf, Rf≦TLψω ｓ Pile foundation that meets the above requirements.

2. The ground in the certain section is sandy / gravelly ground, and the average N value of the sandy / gravelly ground in the certain section is N ｓ and the characteristic value T and the average N value N ｓ The relationship between T=A+B×N ｓ The pile foundation of claim 1 which satisfies the above.

3. When the hardener does not contain an expansion agent, The A is 25≦A≦35, The B is 4.5≦B≦5.

5. The pile foundation of claim 2.

4. When the hardening material contains an expansion material, A is 0, The B is 9.0≦B≦10.

0. The pile foundation of claim 2.

5. The ground in the certain section is clayey ground, and the average value of the uniaxial compressive strength of the clayey ground in the certain section is q ｕ and the characteristic value T and the average value q of the uniaxial compressive strength ｕ The relationship between T=A+B×q ｕ The pile foundation of claim 1 which satisfies the above.

6. When the hardener does not contain an expansion agent, The A is 15≦A≦25, The B is 0.5≦B≦1.0, The pile foundation of claim 5.

7. When the hardening material contains an expansion material, A is 0, The B is 0.5≦B≦1.

5. The pile foundation of claim 5.

8. A method for designing a pile foundation including a pile in which a pile body having at least one of a convex portion and a concave portion on its peripheral surface is embedded in a pile hole formed by excavating the ground via a hardening material, and the hardening material is hardened to be integrated with the pile body, Let T be a characteristic value related to the frictional force that reflects the strength of the ground around the pile, L be the length of a certain section where the pile contacts the ground, the ground in the certain section has the same geology, ψ be the circumference of the pile body, and ω be the expansion ratio, which is the ratio of the excavation diameter of the pile hole to the standard excavation diameter determined based on the pile diameter of the pile body. ｓ When the target value of the peripheral friction force of the pile against the pile hole in the certain section is Rf, Rf≦TLψω ｓ A method for designing the pile foundation to satisfy the above.

9. The ground in the certain section is sandy / gravelly ground, and the average N value of the sandy / gravelly ground in the certain section is N ｓ and the characteristic value T and the average N value N ｓ The relationship between T=A+B×N ｓ The pile foundation design method according to claim 8, which satisfies the above.

10. When the hardener does not contain an expansion agent, The A is 25≦A≦35, The B is 4.5≦B≦5.

5. The pile foundation design method according to claim 9.

11. When the hardening material contains an expansion material, A is 0, The B is 9.0≦B≦10.

0. The pile foundation design method according to claim 9.

12. The ground in the certain section is clayey ground, and the average value of the uniaxial compressive strength of the clayey ground in the certain section is q ｕ and the characteristic value T and the average value q of the uniaxial compressive strength ｕ The relationship between T=A+B×q ｕ The pile foundation design method according to claim 8, which satisfies the above.

13. When the hardener does not contain an expansion agent, The A is 15≦A≦25, The B is 0.5≦B≦1.0, The pile foundation design method according to claim 12.

14. When the hardening material contains an expansion material, A is 0, The B is 0.5≦B≦1.

5. The pile foundation design method according to claim 12.

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