JP7755136B2 - Pile foundations and their design methods - Google Patents

Description

Article 30, Paragraph 2 of the Patent Act applies. Published on January 22, 2021, at http://www.japanpile.co.jp/ and http://www.japanpile.co.jp/method/buildingtech/smart-magnum/

Article 30, paragraph 2 of the Patent Act applies. January 22, 2021: Leaflet "Smart-MAGNUM Construction Method" by Japan Pile Co., Ltd. February 15, 2021: Pamphlet "Smart-MAGNUM Construction Method" by Japan Pile Co., Ltd. February 1, 2021: "Smart-MAGNUM Construction Method Construction Guidelines and Commentary" published by Japan Pile Co., Ltd.

Patent Act Article 30, Paragraph 2 applied. Announced at Smart-MAGNUM construction method seminar. Date: February 21, 2021. Location: Daiichi Central Building No. 1 (6-30 Honmachi, Kita-ku, Okayama City, Okayama Prefecture). Date: February 26, 2021. Location: DAIWA River Gate (36-2 Nihonbashi Hakozakicho, Chuo-ku, Tokyo). Date: February 28, 2021. Location: Hokkaido Construction Hall (1-1 Kita 4-jo Nishi 3T, Chuo-ku, Sapporo City, Hokkaido). Date: March 7, 2021. Location: Hotel Kumamoto Terrsa (28-51 Suizenji Park, Chuo-ku, Kumamoto City, Kumamoto Prefecture). Date: March 14, 2021. Location: CIVI Training Center Shin-Osaka East (1-19-4 Higashinakajima, Higashiyodogawa-ku, Osaka City, Osaka Prefecture, Shin-Osaka NLC Building). Date: March 21, 2021 Location: Sakae Gas Building (3-15-33 Sakae, Naka-ku, Nagoya, Aichi Prefecture) Date: March 28, 2021 Location: C1V1 Training Center Nihonbashi (Quattro Muromachi Building, 4-1-6 Muromachi, Nihonbashi, Chuo-ku, Tokyo)

Applicable to Article 30, Paragraph 2 of the Patent Act. Announced at the Smart-MAGNUM Construction Method Seminar. Date: 4/4/2021. Venue: Niigata Terrsa (185-18 Kaneki, Chuo-ku, Niigata City, Niigata Prefecture). Date: 4/11/2021. Venue: Takamatsu Center Building (2-4-20 Kotobuki-cho, Takamatsu City, Kagawa Prefecture). Date: 4/18/2021. Venue: TKP Preseed Koriyama Conference Center (Hotel Preseed Koriyama, 12-2 Nakamachi, Koriyama City, Fukushima Prefecture). Date: 4/25/2021. Venue: Ishikawa Prefecture Local Industry Promotion Center (2-20 Nunokuratsuki, Kanazawa City, Ishikawa Prefecture). Date: 5/9/2021. Venue: Okinawa Convention Center (4-3-1 Mashiki, Ginowan City, Okinawa Prefecture). Date: May 30, 2021 Location: YIC Studio (2-48 Ogori Kogane-cho, Yamaguchi City, Yamaguchi Prefecture) Date: June 6, 2021 Location: Miyagi Prefectural Construction Industry Hall 1F Large Conference Room (2-48 Shikura-cho, Aoba-ku, Sendai City, Miyagi Prefecture) Date: June 23, 2021 Location: DAIWA River Gate (36-2 Hakozaki-cho, Nihonbashi, Chuo-ku, Tokyo) Date: June 27, 2021 Location: CIVI Training Center Nihonbashi (Quattro Muromachi Building, 4-1-6 Muromachi, Nihonbashi, Chuo-ku, Kyoto)

Patent Act Article 30, Paragraph 2 applied Announced at Smart-MAGNUM construction method seminar Event date: July 25, 2021 Venue: Reference Ekimae Building, rental conference room, 2nd floor, Conference Room T (1-16-14 Hakataekimae, Hakata-ku, Fukuoka City) Event date: July 26, 2021 Venue: Fifth Hakata Kaisei Building, 10th floor conference room (1-18-25 Hakataekimae, Hakata-ku, Fukuoka City) Event date: August 1, 2021 Venue: Hokkaido Construction Hall, 9th floor, Large Hall (1-1 Kita 4-jo Nishi 3-chome, Chuo-ku, Sapporo City) Event date: August 23, 2021 Venue: Hiroshima YMCA International Culture Center, Main Building, 4th floor, Room 406 (7-11 Hatchobori, Naka-ku, Hiroshima City, Hiroshima Prefecture) Event date: August 29, 2021 Venue: MEDIA SPACE KNOBY (Media Space Kenobi) (3-3-24 Marifu-cho, Iwakuni City, Yamaguchi Prefecture) Date: September 5, 2021 Location: Tosu Chamber of Commerce and Industry (Tosu Chamber of Commerce and Industry Association) Tosu Chamber of Commerce and Industry Center Conference Room (2-1 Wakasakura, Fujiki-cho, Tosu City, Saga Prefecture) Date: September 12, 2021 Location: EXC Construction Co., Ltd. Company Office (4084-1 Hiraide, Tatsuno-cho, Kamiina-gun, Nagano Prefecture)

Article 30, Paragraph 2 of the Patent Act applies. Published in the following publications: April 1, 2021, COPITA2021, 4. No. 54, pp. 74-75, Concrete Pile and Pole Association, 3F, Nippon Kochiku Building 2, 2-7-15 Hamamatsucho, Minato-ku, Kyoto, Japan; April 1, 2021, GBRC Vol. 46 No. 2, 2021.4 (No. 184), p. 59, General Building Research Corporation of Japan, 5-8-1 Fujishirodai, Suita City, Osaka Prefecture; July 1, 2021, GBRC Vol. 46 No. 3, 2021.7 (No. 185), p. 67, General Building Research Corporation of Japan, 5-8-1 Fujishirodai, Suita City, Osaka Prefecture.

This invention relates to pile foundations and their design methods.

A pile foundation typically includes multiple piles. For example, bored piles are used for the piles. Boreholes are excavated in the ground, and borehole piles are constructed by mixing cement milk and excavated soil 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.

Japanese Patent Application Laid-Open No. 2005-98108

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 surface friction force acting from the ground on the surface of the pile. Surface friction force is thought to be affected by the excavation diameter of the pile hole. However, there has been no quantitative or formal evaluation of the effect of the excavation diameter on surface friction force, and no established evaluation method has been established. For this reason, conventional evaluation methods have not been able to be said to be appropriate for evaluating surface friction force.

The purpose of this invention is to provide a pile foundation design method and pile foundation that can appropriately evaluate the bearing capacity that piles receive from the ground.

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 created by excavating the ground via a hardening material, and the hardening material is hardened to be integrated with the pile body, wherein, when a characteristic value related to friction force reflecting the strength of the ground around the pile is T, the length of a certain section where the pile contacts the ground is L, the ground in the certain section has the same geology, the perimeter of the pile body is ψ, 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 is _ωs , and the target value of the peripheral friction force of the pile against the pile hole in the certain section is Rf, Rf≦ _TLψωs is satisfied.

According to this type of pile foundation, the expansion ratio _ωs , 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 added to the evaluation criteria for the peripheral friction force of the pile, so that the bearing capacity that the pile receives from the ground can be appropriately evaluated.

Another aspect of the design method for a pile foundation 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 created by excavating the ground via a hardening material, and the hardening material is hardened to be integrated with the pile body, wherein, where T is a characteristic value related to frictional force reflecting the strength of the ground around the pile, L is the length of a certain section where the pile is in contact with the ground, the certain section of ground has the same geology, ψ is the perimeter of the pile body, _ωs is 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, and Rf is a target value of the peripheral friction force of the pile against the pile hole in the certain section, the pile foundation is designed to satisfy Rf≦ _TLψωs .

According to this type of pile foundation design method, the expansion ratio _ωs , 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 added to the evaluation criteria for the peripheral friction force of the pile, so that the bearing capacity that the pile receives from the ground can be appropriately evaluated.

The characteristic value T varies depending on the geology of the ground and the type of hardening material as follows:
When the ground in a certain section is sandy/gravelly ground and the average N-value of the sandy/gravelly ground in the certain section is _Ns , the relationship between the characteristic value T and the average N-value _Ns satisfies T = A + B x _Ns . When the hardening material does not contain an expansive additive, A is 25≦A≦35, and B is 4.5≦B≦5.5. When the hardening material contains an expansive additive, A is 0, and B is 9.0≦B≦10.0.

When the ground in a certain section is clayey ground and the average value of the unconfined compressive strength of the clayey ground in the certain section is _qu , the relationship between the characteristic value T and the average value of the unconfined compressive strength _qu satisfies T = A + B × _qu . When the hardening material does not contain an expansive additive, A is 15≦A≦25, and B is 0.5≦B≦1.0. When the hardening material contains an expansive additive, A is 0, and B is 0.5≦B≦1.5.

This invention provides a pile foundation design method and pile foundation that can appropriately evaluate the bearing capacity that piles receive from the ground.

FIG. 1 is a schematic diagram showing a pile foundation according to an embodiment. FIG. 2 is a schematic diagram for explaining the peripheral friction force of the pile included in the pile foundation according to the embodiment. FIG. 3 is a diagram for explaining a method for designing a pile foundation according to the embodiment. Figure 4 shows the results of a load test in which a standard pile using a nodular pile was installed in a pile hole in sandy or gravelly ground, and plotted as a relationship between the average N value and the skin friction resistance stress, along with data on the calculation formula. Figure 5 shows the results of a load test in which a circumferentially reinforced pile using a 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 circumferential friction resistance stress, along with the calculation formula data. Figure 6 shows the results of a loading test in which a standard pile using a nodular pile was installed in a pile hole in clayey ground, and the data plotted as the relationship between the average uniaxial compressive strength q _u and the peripheral friction resistance stress, together with the data for the calculation formula. Figure 7 shows the results of a load test in which a circumferentially reinforced pile using a nodular pile was installed in a pile hole in clayey ground, and the results are plotted as the relationship between the average uniaxial compressive strength q _u and the circumferential friction resistance stress, along with the data for the calculation formula.

Hereinafter, embodiments will be described with reference to the drawings.
As shown in Figure 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 formed 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 it is sufficient to have at least one pile 8.

The pile 8 has a pile body 2, for example, consisting of two or more prefabricated piles connected axially. The pile body 2 may also be composed of a single prefabricated pile. Prefabricated piles include, for example, 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.

The pile body 2 may have 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 with approximately the same diameter as the straight pile 12, and is integrally provided with multiple annular nodular portions 16 spaced apart in the longitudinal direction on the circumferential surface of the shaft.

In this embodiment, the pile body 2 includes at least one nodular pile 14, but the pile body 2 may also be constructed using other prefabricated piles that have at least one convex or concave portion on their circumferential surface. Examples of such other prefabricated piles include those with grooves on their circumferential surface and those with checkered steel plate wrapped around their circumferential surface.

The pile main body 2 does not necessarily have to include a straight pile 12; for example, it may be made by connecting multiple types of nodular piles, or other prefabricated piles having the above-mentioned convex or concave portions on their peripheral surfaces may be used instead of nodular piles. Alternatively, the pile main body 2 may be constructed by connecting a nodular pile with other prefabricated piles having the above-mentioned convex or concave portions on their peripheral surfaces. 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 peripheral surface.

It is desirable that the length of the pile body 2 be such that the tip of the pile body 2 reaches the supporting layer 3 of the ground G. For this reason, it is desirable that the pile hole 1 also be formed to a depth that reaches the supporting layer 3. However, the length of the pile body 2 does not necessarily have to be such that the tip reaches the supporting layer 3.

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

In addition to the pile main body 2 described above, the pile 8 has a base protection section 4 that surrounds the tip of the pile main body 2, and a circumferential pile surface section 6 that surrounds the periphery of the pile main body 2. The base protection section 4 and circumferential pile surface section 6 are formed by applying soil cement (hardening agent) between the inner wall surface of the pile hole 1 and the outer periphery of the pile main body 2 and allowing the soil cement to harden. When the soil cement applied to the base protection section 4 and circumferential pile surface section 6 hardens, the base protection section 4 and circumferential pile surface section 6 are integrated with the concrete pile main body 2 to form the pile 8. The circumferential pile surface section 6 is provided continuously above the base protection section 4.

Soil cement is formed by excavating the ground G to form pile holes 1, leaving a predetermined amount of excavated soil in the pile holes 1, injecting a predetermined amount of cement milk into the pile holes 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 holes 1, and the soil cement hardens and becomes one with the pile body 2, thereby forming the pile 8. Note that the hardening material placed between the pile body 2 and the pile holes 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.

The base protection section 4 is provided on the bottom side of the pile hole 1 so as to surround the tip of the pile body 2, primarily to increase the tip bearing force that the ground G (or the supporting layer 3 of the ground G if the tip of the pile body 2 reaches the supporting layer 3) supports at the tip (lower end as shown). The pile peripheral section 6 is provided between the peripheral surface of the pile body 2 and the inner wall surface of the pile hole 1, primarily to increase the peripheral friction force that the peripheral surface of the pile body 2 receives from the ground G.

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, which is a partially enlarged lower end of the pile periphery excavation section 22. A portion of the shaft hole excavated in the ground G by a designated excavator serves as the pile periphery excavation section 22. 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, and is provided on the bottom side of the pile hole 1, for example.

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 circumferential surface is the diameter of the portion where the outer diameter of the pile body is greatest. 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.

The tip of the pile main body 2 is positioned 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 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 along 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.

The bearing force that piles 8 of the above structure receive 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 piles 8 receive from the ground G is the sum of the tip bearing force and the circumferential friction force. When designing the pile foundation 10, the allowable bearing force of each pile 8 of the pile foundation 10 is determined to be the smaller of the bearing force that each pile 8 receives from the ground G or the material strength of the pile body 2 of each pile 8.

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 perimeter excavation section 22 in order to increase the allowable bearing capacity of the pile 8, the difference between the diameter of the pile perimeter excavation section 22 and the diameter of the enlarged excavation section 24 in the pile hole 1 will become greater. In this case, it becomes increasingly 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 increase.

Furthermore, if only the enlarged excavation section 24 is enlarged as described above, the inner diameter of the pile periphery 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 likelihood that the pile body 2 will come into contact with the inner wall of the pile hole 1, causing damage to the inner wall 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 more difficult.

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 circumferential 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 peripheral friction force of the pile 8 is increased by adjusting the expansion ratio _ωs of the pile hole 1 in the pile peripheral portion 6, thereby increasing the bearing capacity that the pile 8 receives from the ground G.

In other words, according to the design method of this embodiment, the expansion ratio _ωs at the pile peripheral surface portion 6 can be set to an appropriate value, the difference in diameter between the pile peripheral excavation portion 22 and the enlarged excavation portion 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.

The 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 for this embodiment applies to the nodular piles 14 of each pile 8 of the pile foundation 10, and not to the straight piles 12. The piles 8 described up to this point have included those with a structure in which straight piles 12 are arranged in the pile-periphery excavation portion 22 of the pile hole 1, but the piles 8 in the following description will be those with a structure in which nodular piles 14 are arranged in the pile-periphery excavation portion 22.

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 this 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 names may differ depending on the particle size distribution of the soil particles that make up the ground G. Therefore, when determining the certain section, consideration is also given to dividing the soil type by this soil type name.

The pile foundation 10 is then designed so that the peripheral friction force of the pile 8 in this fixed 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 fixed section receives from the ground G, out of the load that the pile foundation 10 receives from the building 100 (Figure 1), and is the target value for the peripheral friction force of the pile 8 when designing the pile foundation 10.

Let T be a characteristic value related to the friction force reflecting the strength of the ground G around the pile 8 in the above-mentioned certain section, ψ be the perimeter of the nodular portion 16 of the nodular pile 14 existing in the certain section, ωs be the ratio (D _es /D ss ) of the excavation diameter D _es of the pile hole 1 to the standard reference excavation diameter D _ss determined based on the diameter D _os of the nodular portion 16 of the nodular pile 14 existing in the certain section (i.e., the pile diameter of the pile _{body 2} ), and let _Rf be the target value of the peripheral friction force that the pile 8 in the certain section receives from the ground G.
Rf≦ _TLψωs ...(1)
The pile foundation 10 is designed to satisfy the following.

In the claims, the perimeter ψ of the pile body is the perimeter of the portion where the outer diameter of the pile body is maximum in a certain section, and the pile diameter in the claims is the diameter of the portion where the outer diameter of the pile body is maximum in a certain section. 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 standard reference excavation diameter _Dss determined based on the pile diameter _Dos of the pile body 2 is approximately the pile diameter _Dos + 50 mm.

That is, according to the design method of this embodiment, by adjusting the expansion ratio _ωs of the pile peripheral portion 6, it is possible to make the peripheral friction force of the pile 8 present in a certain section of the length L a value greater than the target value Rf. Therefore, according to this embodiment, it is possible to control the peripheral friction force acting on the pile 8 from the ground G by changing the expansion ratio _ωs . Therefore, according to this embodiment, it is possible to appropriately evaluate the peripheral friction force of the pile 8 and therefore to appropriately evaluate the bearing capacity that the pile 8 receives from the ground G.

Furthermore, according to this embodiment, the difference in diameter between the pile perimeter excavation section 22 and the enlarged excavation section 24 of the pile hole 1 in which the pile foundation 10 is constructed can be reduced (or in some cases eliminated), making construction possible using mechanical excavation equipment. This reduces construction costs and makes construction easier.

In the above description of the design method, the ratio (D _es /D _ss ) of the excavation diameter D _es of the pile hole 1 to the reference excavation diameter D _ss obtained by adding 50 mm to the diameter D _os of the node portion 16 was defined as the expansion ratio ω _s of the pile peripheral portion 6. However, the reference excavation diameter D _ss may be several tens of mm larger than the diameter D _os of the node portion 16, and is not limited to 50 mm.

As shown in Figure 3, the characteristic value T in 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).

When the ground G around the pile hole 1 in a certain section of length L is sandy/gravel ground and its average N value is _Ns , the characteristic value T of formula (1) is
T=A+BN _s ...(2)
It can be expressed as:

The characteristic value T is a value obtained by dividing the peripheral friction force between the ground G and the pile hole 1 in the above-mentioned fixed section by the peripheral length ψ of the pile body 2 × the fixed section L. The peripheral friction force varies 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 the fixed section L) by using coefficients A and B of the linear function. Note that coefficients A and B can be determined from the relationship between Ns and T confirmed by experiments, etc., and coefficient A corresponds to the Y-intercept of the linear function of formula (2), and coefficient B corresponds to the gradient of the linear function of formula (2).

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, and shows the relationship between the average N value of the ground and the peripheral friction resistance stress (friction resistance force per unit area) acting on the actual pile 8. 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).

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 a range that satisfies the calculated value≦measured value. The calculation formula shown by the solid line in Figure 4 is T = 30 + 5.5 N _s . Looking at Figure 4, it can be seen that all of the measured values exceed the calculation formula. In other words, it has been proven that when a standard pile 8 is installed in sandy or gravelly ground, the following formula (1-1) holds true, with the characteristic value T set to (30 + 5.5 N _s ).
Rf≦(30+5.5N _s ) Lψω _s ...(1-1)

The dashed-dotted line in Figure 4 shows the calculated value entered into equation (2) when coefficient A is set to the maximum value of the above range (A = 42) and coefficient B is set to the minimum value (B = 0), while the dashed-double-dotted line in Figure 4 shows the calculated value entered into equation (2) when coefficient A is set to the minimum value (A = 0) and coefficient B is set to the maximum value of the above range (B = 6.8). In other words, the maximum value of coefficient A in equation (2) based on the actual measured values in Figure 4 is 42, and the maximum value of coefficient B is 6.8.

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 25≦A≦35, and coefficient B is preferably in the range 4.5≦B≦5.5.

The experimental data in Figure 5 plots the results of multiple load tests on a circumferentially reinforced pile 8 that was actually constructed in a pile hole 1 in sandy and gravelly ground using a nodular pile 14, and shows the relationship between the average N value of the ground and the circumferential friction resistance stress acting on the actual pile 8. The circumferentially reinforced pile 8 referred to here is a pile whose circumferential portion 6 is constructed from soil cement containing anhydrous gypsum (expansive material).

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 a range that satisfies the calculated value≦measured value. The calculation formula shown by the solid line in Figure 5 is T = 9.5 N _s . Looking at Figure 5, it can be seen that all of the measured values exceed the calculation formula. In other words, it has been proven that when a perimeter-reinforced pile 8 is installed in sandy or gravelly ground, the following formula (1-2) with characteristic value T of (9.5 N _s ) holds true.
Rf≦(9.5N _s ) Lψω _s ...(1-2)

The dashed-dotted line in Figure 5 shows the calculated value entered into equation (2) when coefficient A is set to the maximum value of the above range (A = 48) and coefficient B is set to the minimum value (B = 0), while the dashed-double-dotted line in Figure 5 shows the calculated value entered into equation (2) when coefficient A is set to the minimum value (A = 0) and coefficient B is set to the maximum value of the above range (B = 9.8). In other words, it can be said that the maximum value of coefficient A in equation (2) based on the actual measured values in Figure 5 is 48, and the maximum value of coefficient B is 9.8.

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 5, it can be said that coefficient A is preferably 0, and coefficient B is preferably in the range 9.0≦B≦10.0.

When the ground G around the pile hole 1 in a certain section of length L is clayey ground and the average value of its unconfined compressive strength is _qu , the characteristic value T of formula (1) is
T=A+Bq _u ...(3)
It can be expressed as:

The characteristic value T is a value obtained by dividing the peripheral friction force between the ground G and the pile hole 1 in the above-mentioned fixed section by the circumferential length ψ of the pile body 2 × the fixed section L. The characteristic value T can be calculated from q _u (the average value of the uniaxial compressive strength of the clayey ground in the fixed section L) by using coefficients A and B of the linear function. Note that coefficients A and B can be determined from the relationship between q _u and T confirmed by experiments, etc., and coefficient A corresponds to the Y-intercept of the linear function of formula (3), and coefficient B corresponds to the gradient of the linear function of formula (3).

The experimental data in Figure 6 is a plot of several examples of the results of load tests on standard piles 8 that were actually installed in pile holes 1 in clayey ground using nodular piles 14, and shows the relationship between the average uniaxial compressive strength of the ground and the peripheral friction resistance stress acting on the actual piles 8.

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 a range that satisfies the calculated value≦measured value. The calculation formula shown by the solid line in Figure 6 is T = 20 + 0.5q _u . Looking at Figure 6, it can be seen that all of the measured values exceed the calculation formula. In other words, it has been proven that when a standard pile 8 is installed in clayey ground, the following formula (1-3) holds true, with the characteristic value T set to (20 + 0.5q _u ).
Rf≦(20+0.5q _u ) Lψω _s ...(1-3)

The dashed-dotted line in Figure 6 shows the calculated value entered into equation (3) when coefficient A is set to the maximum value of the above range (A = 37) and coefficient B is set to the minimum value (B = 0), while the dashed-double-dotted line in Figure 6 shows the calculated value entered into equation (3) when coefficient A is set to the minimum value (A = 0) and coefficient B is set to the maximum value of the above range (B = 0.66). In other words, the maximum value of coefficient A in equation (3) based on the actual measured values in Figure 6 is 37, and the maximum value of coefficient B is 0.66.

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 6, it can be said that coefficient A is preferably in the range 15≦A≦25, and coefficient B is preferably in the range 0.5≦B≦1.0.

The experimental data in Figure 7 plots the results of multiple load tests on circumferentially reinforced piles 8 that were actually installed in pile holes 1 in clayey ground using nodular piles 14, and shows the relationship between the average uniaxial compressive strength of the ground and the circumferential friction resistance stress acting on the actual piles 8.

The solid line in Figure 7 shows a calculation formula, which is an example of formula (3), and is based on calculated values obtained by appropriately setting coefficients A and B within a range that satisfies the condition that the calculated value is less than or equal to the measured value. The calculation formula shown by the solid line in Figure 7 is T = q _u . Looking at Figure 7, it can be seen that all of the measured values exceed the calculation formula. In other words, it has been proven that when a perimeter-reinforced pile foundation 10 is constructed on clayey ground, the following formula (1-4), in which the characteristic value T is (q _u ), holds true.
Rf≦(q _u )Lψω _s ...(1-4)

The dashed-dotted line in Figure 7 shows the calculated value entered into equation (3) when coefficient A is set to the maximum value of the above range (A = 37) and coefficient B is set to the minimum value (B = 0), while the dashed-double-dotted line in Figure 7 shows the calculated value entered into equation (3) when coefficient A is set to the minimum value (A = 0) and coefficient B is set to the maximum value of the above range (B = 1.0). In other words, it can be said that the maximum value of coefficient A in equation (3) based on the actual measured values in Figure 7 is 37, and the maximum value of coefficient B is 1.0.

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 7, it can be said that coefficient A is preferably 0, and coefficient B is preferably in the range 0.5≦B≦1.5.

As described above, according to this embodiment, the peripheral friction force can be adjusted by adjusting the expansion ratio _ωs of the pile peripheral portion 6 of each pile 8 of the pile foundation 10, and the peripheral friction force of the pile 8 can be appropriately evaluated. 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.

Furthermore, according to this embodiment, the difference in diameter between the pile-periphery excavation portion 22 and the enlarged excavation portion 24 of the pile hole 1 for constructing each pile 8 of the pile foundation 10 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.

Furthermore, according to this embodiment, for example, when excavating the pile hole 1, the diameter of the pile circumferential excavation portion 22 (i.e., the expansion ratio ω _s of the pile circumferential excavation portion 22) is determined first, and the amount by which the bearing capacity of the pile 8 is insufficient relative to the allowable bearing capacity is calculated, and the shortage can be compensated for by adjusting the diameter of the expanded excavation portion 24. This increases the degree of freedom in designing the pile foundation 10, making it easier to design the pile foundation 10.

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,
The characteristic value relating to the friction force reflecting the strength of the ground around the pile is T, the length of a certain section where the pile is in contact with the ground is L, the ground in the certain section is of the same geology, the circumference of the pile body is ψ, 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 is ωs _, and the friction force of the pile in the certain section is
When the target value of the peripheral friction force is Rf,
Rf≦ _TLψωs
Pile foundation that meets the above requirements.
[2]
The ground in the certain section is sandy/gravelly ground, the average N value of the sandy/gravelly ground in the certain section is Ns _, and the relationship between the characteristic value T and the average N value _Ns is
T = A + B × N _s
A pile foundation that satisfies [1].
[3]
When the hardener does not contain an expansion agent,
The 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, the average value of the uniaxial compressive strength of the clayey ground in the certain section is q _u , and the relationship between the characteristic value T and the average value q _u of the uniaxial compressive strength
but,
T = A + B × q _u
A pile foundation that satisfies [1].
[6]
When the hardener does not contain an expansion agent,
The 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,
The characteristic value relating to the friction force reflecting the strength of the ground around the pile is T, the length of a certain section where the pile is in contact with the ground is L, the ground in the certain section is of the same geology, the circumference of the pile body is ψ, 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 is ωs _, and the friction force of the pile in the certain section is
When the target value of the peripheral friction force is Rf,
Rf≦ _TLψωs
A method for designing the pile foundation to satisfy the above.
[9]
The ground in the certain section is sandy/gravelly ground, the average N value of the sandy/gravelly ground in the certain section is Ns _, and the relationship between the characteristic value T and the average N value _Ns is
T = A + B × N _s
The pile foundation design method of [8] 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.
[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, the average value of the uniaxial compressive strength of the clayey ground in the certain section is q _u , and the relationship between the characteristic value T and the average value q _u of the uniaxial compressive strength
but,
T = A + B × q _u
The pile foundation design method of [8] 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,
[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.

1...Pile hole, 2...Pile body, 3...Supporting layer, 4...Foot protection 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 (14)

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,
When a characteristic value related to the friction force reflecting the strength of the ground around the pile is T, the length of a certain section where the pile is in contact with the ground is L, the ground in the certain section has the same geology, the perimeter of the pile body is ψ, 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 _ωs , and a target value of the peripheral friction force of the pile against the pile hole in the certain section is Rf,
Rf≦ _TLψωs
Pile foundation that meets the above requirements. The ground in the certain section is sandy/gravelly ground, the average N value of the sandy/gravelly ground in the certain section is _Ns , and the relationship between the characteristic value T and the average N value _Ns is
T = A + B × N _s
The pile foundation of claim 1 which satisfies the above. 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. 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. The ground in the certain section is clayey ground, the average value of the uniaxial compressive strength of the clayey ground in the certain section is q _u , and the relationship between the characteristic value T and the average value q _u of the uniaxial compressive strength is
T = A + B × q _u
The pile foundation of claim 1 which satisfies the above. 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. 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. 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,
When a characteristic value related to the friction force reflecting the strength of the ground around the pile is T, the length of a certain section where the pile is in contact with the ground is L, the ground in the certain section has the same geology, the perimeter of the pile body is ψ, 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 _ωs , and a target value of the peripheral friction force of the pile against the pile hole in the certain section is Rf,
Rf≦ _TLψωs
A method for designing the pile foundation to satisfy the above. The ground in the certain section is sandy/gravelly ground, the average N value of the sandy/gravelly ground in the certain section is _Ns , and the relationship between the characteristic value T and the average N value _Ns is
T = A + B × N _s
The pile foundation design method according to claim 8, which satisfies the above. 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. 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. The ground in the certain section is clayey ground, the average value of the uniaxial compressive strength of the clayey ground in the certain section is q _u , and the relationship between the characteristic value T and the average value q _u of the uniaxial compressive strength is
T = A + B × q _u
The pile foundation design method according to claim 8, which satisfies the above. 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. 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.