Pile design method

Abstract

To enable piles to be designed even without ground survey data.SOLUTION: A pile design method includes: shallow layer ground modeling step (S31) of modeling a shallow layer ground based on a shallow layer N value that can be secured in a shallow layer ground where an upper part of a pile is located; deep layer ground modeling step (S32) of modeling a deep layer ground based on a deep layer N value required for a deep layer ground where a lower part of the pile is located; and middle layer ground modeling step (S33) of modeling a middle layer ground by setting zero as an N value for a middle layer ground where a middle part of the pile is located. An N value obtained by surface layer improvement is set as the shallow layer N value. The deep layer N value is set to an N value that can withstand a compressive axial force generated by a total weight of an upper structure and a pile's own weight.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a method for designing piles, and more particularly to a method for designing precast piles. [Background technology]

[0002] When designing piles that form the foundations of building structures, it is necessary to analyze the stresses acting on the piles buried in the ground and select piles that can withstand those stresses. Patent Document 1 describes a pile design system that automates the work of designing piles while taking into account the deformation performance of the piles. Patent Document 1 deals with designing concrete-filled steel pipe piles and concrete-filled steel pipes. As described in Patent Document 1, to analyze the stress acting on a pile, it is necessary to conduct a ground survey to determine the N-value of the ground, and then set a ground horizontal spring in the ground modeled based on the N-value. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2006-161363 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the past, piles could not be designed without conducting a soil survey. This resulted in the problem that it took time from the architectural planning stage to the selection of piles. Furthermore, at the architectural planning stage of a building structure, the size of the piles required was not clear, which meant that the site area, construction period, construction costs, etc. required for pile construction were not clear. Patent Document 1 describes automating the work of designing piles, but does not take into consideration how to handle cases where there is no ground investigation data when designing piles. The present invention has been made in consideration of the above circumstances, and aims to enable pile design even without ground investigation data. [Means for solving the problem]

[0005] In order to solve the above-mentioned problems, the present invention provides a method for designing a single pile that is driven into the ground and supports a superstructure joined to the upper part, the method comprising the steps of: a shallow ground modeling step of setting at least two shallow ground horizontal springs at a predetermined interval in appropriate locations in the shallow ground based on a shallow N-value that can be secured in the shallow ground where the upper part of the pile is located, to model the shallow ground; and a deep ground modeling step of setting at least two deep ground horizontal springs at a predetermined interval in appropriate locations in the deep ground based on a deep N-value required for the deep ground where the lower part of the pile is located, to model the deep ground. the method includes a middle ground modeling process for setting an N value of 0 for the middle ground where the middle part of the pile is located and setting one or more middle ground horizontal springs at predetermined intervals at appropriate locations within the middle ground to model the middle ground; a stress analysis process for analyzing the stress state of the pile when a bending moment and a shear force are applied from the superstructure to the pile head; and a testing process for testing whether the pile can withstand the stress state, wherein the shallow ground is set to the depth range of the ground where surface improvement is planned, and the shallow ground N value is set to the N value obtained by the surface improvement. [Effects of the Invention]

[0006] According to the present invention, piles can be designed even without ground investigation data. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a partial cross-sectional front view showing a pile to be designed according to an embodiment of the present invention and a part of a superstructure supported by the pile. FIG. [Figure 2] 1(a) to 1(f) are schematic diagrams showing an example of a pile construction method. [Figure 3] 10(a) and 10(b) are flowcharts showing a pile design method according to one embodiment of the present invention. [Figure 4]This is a setting model diagram showing the positional relationship between the ground horizontal spring set in the ground and the piles and surface improvement part. [Figure 5] FIG. 5 is a diagram showing an analytical model of the piles and ground corresponding to FIG. 4. [Figure 6] 1A and 1B are diagrams showing examples of stress analysis results, where (a) is a bending moment diagram and (b) is a shear force diagram. [Figure 7] FIG. 10 is a schematic front view showing a pile to be designed according to another embodiment of the present invention and a part of a superstructure supported by the pile. DETAILED DESCRIPTION OF THE INVENTION

[0008] The present invention will be described in detail below using the embodiments shown in the drawings. However, unless otherwise specified, the components, types, combinations, shapes, relative positions, etc. described in these embodiments are merely illustrative examples and do not intend to limit the scope of the present invention. Furthermore, unless a particular contradiction arises, the configurations described in each embodiment can be appropriately combined and implemented.

[0009] [Design object] Figure 1 is a partial cross-sectional front view showing a pile to be designed according to one embodiment of the present invention and a part of the superstructure supported by the pile. In the figure, Ax is the axis of the superstructure 10 and the pile 40, both of which extend vertically. The superstructure 10 is a tower-like structure such as a radio tower. A radio tower supports an object such as an antenna device for a mobile phone. The superstructure 10 is configured to be directly connectable to a pile 40 and to be supported by a single pile 40. The superstructure 10 has a base 11 joined to the pile 40, and a tubular support 21 whose lower end is joined to the base 11.

[0010] <Pedestal> The entire base 11 is made of steel, and each part is joined and integrated by welding. The base 11 has a flat base plate 13, a hollow cylindrical tapered steel pipe 15 protruding upward from the center of the upper surface of the base plate 13, and a plurality of reinforcing ribs 17, 17... that are arranged radially around the outer periphery of the tapered steel pipe 15 and have two adjacent sides joined to the upper surface of the base plate 13 and the outer periphery of the tapered steel pipe 15, respectively. The base plate 13 is roughly disk-shaped and protrudes radially outward like a flange from the lower end of the tapered steel pipe 15. The base plate 13 has a plurality of fastening holes that penetrate the tapered steel pipe 15 at appropriate positions on its outer periphery and at appropriate positions on its inner periphery. The base plate 13 is fastened to a top plate 47, which is placed at the top of the pile 40, via a joint plate 30 using fastening members F1, F2 such as bolts and nuts. The tapered steel pipe 15 has a tapered shape in which the inner and outer diameters gradually decrease upward. The upper end of the tapered steel pipe 15 is open, and the lower end is joined to the base plate 13 and closed. The reinforcing ribs 17, 17... are plate-like members of roughly triangular or trapezoidal shape, with the length of their protrusion from the outer circumferential surface of the tapered steel pipe 15 gradually decreasing upward. Multiple reinforcing ribs 17, 17... are arranged at equal intervals at predetermined intervals around the circumference of the tapered steel pipe 15. The reinforcing ribs 17, 17... are arranged to extend vertically along the axis Ax of the tapered steel pipe 15. The reinforcing ribs 17, 17... exert resistance to the bending moment and shear force acting on the base 11 due to the horizontal displacement (swing) of the support 21.

[0011] <Strut> The upper part of the support pillar 21 supports an antenna device (supported object) for a mobile phone or the like. A steel pipe can be used for the support pillar 21. However, in order to reduce the compressive axial force acting on the pile 40, it is desirable to use a fiber-reinforced plastic pipe, particularly a carbon-fiber-reinforced plastic pipe, for the support pillar 21, which is lighter than a steel pipe and can exhibit the bending strength required to withstand the extremely rare occurrence of strong winds. A tapered steel pipe 15 is inserted into the hollow portion of the support 21 from its lower end opening, and the support 21 and the tapered steel pipe 15 overlap at the lower end of the support 21. The support 21 and the tapered steel pipe 15 are fastened and integrated together using a fastening member F3 such as a blind rivet that can fasten them together by operating only from the outer periphery.

[0012] <Pile> The pile 40 (substructure) to be designed in this embodiment is a rotary penetration type steel pipe pile, a prefabricated pile made entirely of steel. The pile 40 is a support pile whose tip is supported by ground (deep ground) having a predetermined N value. The pile 40 includes a roughly cylindrical pile body 41, a pair of tip wings 43, 43 arranged at the lower end (tip) of the pile body 41 and capable of screwing into the ground, a top plate 47 joined to the upper end (pile head) of the pile body 41, and a plurality of rib plates 49, 49... each of which has two adjacent sides fixed by welding to the outer circumferential surface of the pile body 41 and the lower surface of the top plate 47. The pile 40 may further include excavation blades 45, 45 protruding downward from the lower end of the pile body 41. The components constituting the pile 40 are joined and integrated by welding or the like.

[0013] The pile 40 is configured by sequentially joining multiple axially separated segments in the axial direction according to the length of embedment in the ground. As an example, the pile 40 shown in FIG. 1 includes a lower member 51 located at the tip of the pile 40 and including tip wings 43, 43 and the lower end of the pile body 41; an upper member 53 located at the upper end of the pile 40 and including a top plate 47, rib plates 49, 49, ..., and the upper end of the pile body 41; and an intermediate member 55 located in the axial middle and constituting the intermediate portion of the pile body 41. The lower member 51, intermediate member 55, and upper member 53 are sequentially joined by joints (welded joints or mechanical joints) 41a. Depending on the total axial length of the pile 40, one or more intermediate members 55 may be omitted or provided in the axial direction.

[0014] The pile body 41 is made of a roughly cylindrical steel pipe. Depending on the required embedded length, the pile body 41 has a configuration in which multiple short steel pipes are joined with joints 41a to increase the overall length. Figure 1 shows a configuration in which the pile body 41 is divided into three parts in the axial direction.

[0015] The tip wings 43, 43 are made of semicircular or fan-shaped steel material divided into two in the circumferential direction. The tip wings 43, 43 are welded to the pile body 41 in a state inclined in different directions relative to a plane perpendicular to the axis Ax of the pile body 41. The tip wings 43, 43 can be arranged rotationally symmetrically with the axis Ax as the axis of symmetry. The tip wings 43, 43 shown in the figure have a half-flange shape or a spiral shape protruding radially outward from the outer circumferential surface of the pile body 41. The tip wings 43, 43 exert a screwing action into the ground when the pile 40 is embedded. After being installed in the ground, the tip wings 43, 43 exert a bearing force (bearing capacity) in the pushing direction (compressive axial force) based on the vertical load of the superstructure 10 and the pile 40. Furthermore, the tip wings 43, 43 exert resistance to pulling out of the pile 40 after being installed in the ground 100. Note that the shape of the tip wings 43, 43 is not limited to this as long as they can exert a screwing action into the ground, a bearing capacity against compressive axial force, and resistance to pulling out at the tip of the pile 40.

[0016] The top plate 47 is roughly disk-shaped and protrudes radially outward from the upper end of the pile body 41 like a flange. The top plate 47 closes the upper end opening of the pile body 41. The top plate 47 has a plurality of fastening holes that penetrate the outer periphery of the pile body 41 at appropriate positions within the surface. The top plate 47 is fastened to the base plate 13 of the pedestal 11 via the joint plate 30 using fastening members F1, F2 such as bolts and nuts. The rib plates 49, 49... are plate-like members having a roughly inverted triangular or inverted trapezoidal shape, with the length of their protrusion from the outer circumferential surface of the pile body 41 gradually decreasing downward. A plurality of the rib plates 49, 49... are arranged radially at equal intervals at predetermined intervals around the circumferential direction of the pile body 41. The rib plates 49, 49... are arranged to extend vertically along the axis Ax of the pile body 41. The rib plates 49, 49... exert resistance to the bending moment and shear force acting on the head of the pile 40 due to the horizontal displacement (swing) of the superstructure 10, thereby preventing deformation of the pile 40.

[0017] <Outline of pile construction procedure> 2(a) to 2(f) are schematic diagrams showing an example of a pile construction method. As shown in Figure 2(a), when embedding a pile 40 in the ground 100, a predetermined area of ​​the ground 100 is first excavated from the ground surface (GL = 0) to a predetermined depth to form a work pit 101 in which welding of the pile body 41, which is a steel pipe, etc. and other work can be performed. The work pit 101 is formed to a size that allows various work required for constructing the pile 40 to be performed. Furthermore, since the work pit 101 will later be the part that will be surface improved, the work pit 101 is formed to satisfy the size required for surface improvement. The size required for surface improvement is the size required to sufficiently reduce the stress acting on the upper end of the pile 40. As an example, the three-dimensional shape of the work pit 101 (excavation portion) is approximately cylindrical. As an example, the diameter of the work pit 101 is set to about four times the diameter of the pile 40 including the rib plates 49, 49.... As an example, the depth of the work pit 101 is set to be at least deeper than the axial length of the upper member 53.

[0018] As shown in Figure 2(b), the screwing action of the tip blades 43, 43 is used to rotate the tip blades 43, 43 and the pile body 41 while driving the pile 40 into the ground from the bottom surface 101a of the work pit 101. If necessary, the pile 40 is driven into the ground while sequentially joining intermediate members 55 with joints 41a according to the embedded length of the pile 40 to increase its length (see Figure 2(c)). As shown in Figure 2(c), after the tip wings 43, 43 reach a predetermined depth in the ground 100, the upper member 53 of the pile 40 is joined to the upper end of the part of the pile 40 buried in the ground (here, the upper end of the intermediate member 55) by a joint 41a. As shown in FIG. 2(d), the base plate 13 of the pedestal 11 is fastened to the top plate 47 of the pile 40 via the joint plate 30 using fastening members F1 and F2. As shown in FIG. 2( e ), concrete, soil cement, cement-based solidifying agent, or other material is filled into the work pit 101 and hardened to form a surface improvement portion 103 of the ground 100 . As shown in FIG. 2( f ), the columns 21 are fastened to the tapered steel pipes 15 of the base 11 using fastening members F3, and the superstructure 10 is supported by the piles 40 .

[0019] 1 and 2 show a configuration in which the base 11 and the pile 40 are fastened and joined using fastening members F1 and F2, but the base 11 and the pile 40 may also be joined by welding. In this case, the joint plate 30 and the top plate 47 can be omitted. That is, the upper end of the pile 40 may be welded to the base plate 13 of the base 11, so that the base plate 13 and the top plate 47 serve as both the base plate 13 and the top plate 47.

[0020] [Design flow: Overview] 3(a) and (b) are flowcharts showing a pile design method according to one embodiment of the present invention. The pile design method includes a step of tentatively selecting piles (S1), a step of calculating the bearing capacity and yield strength of the piles (S2), a step of modeling the piles and ground (S3), a step of stress analysis (S4), and a step of testing (S5).

[0021] <Pile-related design target values> The design target value for the load constantly input to the pile is set, for example, as follows. -Below the long-term allowable bearing capacity. The design target values ​​for piles against earthquakes are set, for example, as follows: -Being below the short-term allowable stress during rare earthquakes. -Below ultimate strength during extremely rare earthquakes. In the unlikely event of an earthquake, the following may be considered: - Vertical seismic force with an axial force ratio of ±0.35 is considered as vertical seismic motion. In addition to horizontal forces, the ground response displacement during earthquake motion, which occurs extremely rarely, is also considered. For example, the bending moment is the square root of the sum of the squares of the horizontal force and the response displacement, and the shear force is the sum of the absolute values ​​of the horizontal force and the response displacement. It is desirable to conduct cross-section testing for earthquake motions that take vertical movements into account. The external force applied to the pile head due to earthquake motion can be determined by time history response analysis.

[0022] The design target values ​​for piles against strong winds are set, for example, as follows: - The stress level remains below the short-term allowable stress level during rare storms. -Below ultimate strength during extremely rare storms. In addition, during storms, vertical earthquake motion and response displacement during earthquake motion are not taken into consideration.

[0023] Here, the horizontal force and overturning moment acting on the superstructure are greater during extremely rare windstorms than during extremely rare earthquake motions. The latter has a large effect on the horizontal allowable stress of the piles, especially on the horizontal allowable stress of the pile tops. For this reason, piles should be considered only during extremely rare windstorms, and consideration of extremely rare earthquake motions may be omitted.

[0024] <<Ground response displacement during extremely rare earthquakes>> For earthquakes that occur extremely rarely, the ground displacement response due to the earthquake is taken into consideration. The ground displacement amplitude at a position x [m] from the ground surface is calculated using the following formula based on the "Guidelines and Commentary on Earthquake-Resistant Construction Methods for Waterworks Facilities (2009 Edition) / Japan Water Works Association." TIFF0007808806000001.tif9150However, Uh(x): Horizontal displacement amplitude of the ground at a depth of x [m] from the ground surface [cm] x: Depth from the ground surface [m] S'v: Velocity response spectrum of bedrock earthquake motion [cm / s] TG: Natural period of surface ground [s] H: Thickness of the surface ground [m]

[0025] <Relationship with the superstructure> In order to analyze the behavior (stress state) of a pile based on the stress applied to the pile from the superstructure, it is assumed that the design of the superstructure that satisfies the specified design goals has been completed before carrying out each process related to the pile design. The design target values ​​of the superstructure can be set in the same way as the design target values ​​of the piles. In other words, the design target values ​​of the superstructure during rare earthquakes and storms can be set to be below the short-term allowable stress, and the design target values ​​of the superstructure during extremely rare earthquakes and storms can be set to be below the ultimate strength. Note that vertical earthquake motion does not need to be taken into account during storms. During extremely rare earthquakes, the seismic force acting in the vertical direction with an axial force ratio of ±0.35 can be taken into account as vertical earthquake motion. During earthquakes and storms, the shear force Q and overturning moment M acting on the superstructure are greatest at the lowest point of the superstructure. When the structure has a configuration in which piles 40 and the superstructure 10 are directly joined, as shown in Figure 1, the stress acting on the lowest point of the superstructure is applied to the pile head. Therefore, the stresses (bending moment M and shear force Q) acting on the lowest point of the superstructure during earthquakes and storms are calculated in advance.

[0026] <<Wind pressure acting on the superstructure>> Wind loads due to rare windstorms are calculated using the following formula, based on Article 87 of the Building Standards Act Enforcement Order and Ministry of Construction Notification No. 1454 of 2000. For extremely rare wind loads, a value calculated by multiplying the rare wind load by 1.5625 (wind speed 1.25 times that of rare winds) is used. Note that extremely rare windstorms refer to windstorms that occur approximately once every 500 years. The wind pressure of rare storms is TIFF0007808806000002.tif6150The velocity pressure of a rare storm is TIFF0007808806000003.tif6150 TIFF0007808806000004.tif6150 TIFF0007808806000005.tif6150 TIFF0007808806000006.tif11150

[0027] however, P: Wind load [kN] A: Pressure receiving area [m^2] q: velocity pressure [N / m^2] H: Height of workpiece [m] Er: Coefficient representing the vertical distribution of mean wind speed Gf: Gust effect coefficient V0: Reference wind speed [m / s] Cf: Wind force coefficient ZG: Value set according to the ground surface roughness classification E and kz are values ​​specified in Ministry of Construction Notification No. 1454 and should be calculated in accordance with that notification.

[0028] In this embodiment, the values ​​relating to wind pressure in Article 87 of the Enforcement Order of the Building Standards Act, which are used in the stress analysis of the superstructure, are set as follows. Regarding the ground surface roughness classification, in order to ensure that a tower-like structure designed using the design method according to this embodiment can be constructed in a general area in Japan, the area where the target tower-like structure is likely to be constructed is set to ground surface roughness classification II (areas with scattered fields and houses), which is the classification in which the superstructure is most susceptible to the extremely rare occurrence of strong winds. Furthermore, in order to apply this to a general area in Japan, the reference wind speed V0 is set to 34 [m / s]. Note that ground surface roughness classification II is on the safe side compared to construction sites with ground surface roughness classifications III and IV.

[0029] <<Seismic forces acting on the superstructure>> Regarding seismic forces, the response value of the superstructure due to earthquakes that occur rarely or extremely rarely is calculated based on time history response analysis. The design input earthquake motion can be determined based on the Time History Response Analysis Building Performance Evaluation Service Manual. Typically, the Hachinohe phase, Kobe phase, random number phase, etc. are used as the notified waves, and the 1940 El Centro, 1968 Hachinohe, 1956 Taft, etc. are used as observed waves. As time history response analysis software, Midas iGen by MidasIT, etc. can be used.

[0030] <Step S1: Tentative pile selection process> As shown below, the pile's projected width B is required to calculate the ground horizontal spring K, so the pile 40 to be analyzed is tentatively selected. The type and inner and outer diameters of the steel material constituting the pile 40 are provisionally selected based on the specifications of the steel pipe pile. The total axial length of the pile 40 is set so that the lower end of the pile 40 reaches a ground depth where a deep N value can appear in the actual ground, which can exert a strength capable of supporting the compressive axial force generated by the total weight of the superstructure 10 and the weight of the pile 40 itself.

[0031] <Step S2: Calculation of pile bearing capacity and yield strength> The vertical bearing capacity of the pile, the horizontal allowable capacity, and the allowable stress are calculated according to the conditions set as design targets. The design bearing capacity of a pile under normal conditions is the sum of the total weight of the superstructure and the weight of the foundation. If the structure is configured so that the pile and the superstructure are directly connected, as shown in Figure 1, the weight of the foundation is zero. The vertical bearing capacity of the pile is calculated according to the pile specifications. In addition, the allowable horizontal strength and allowable stress of the pile are calculated from the standard strength determined by the pile shape, Young's modulus, and material.

[0032] <Step S3: Modeling of piles and ground> Figure 4 is a setting model diagram showing the positional relationship between the ground horizontal springs set in the ground, the piles, and the surface improvement portion. Figure 5 is a diagram showing an analytical model of the piles and ground corresponding to Figure 4. Figures 4 and 5 show an example in which the total axial length of the piles is 10.0 m. In Figure 5, Z000 to Z100 indicate the depth of the ground, K1 to K8 indicate the ground horizontal springs 121 to 125 set at each depth in the ground and their spring constants, and P1 to P14 indicate the nodes of the piles 40 set at each depth in the ground. Each ground horizontal spring is connected to a node located at the corresponding depth.

[0033] In the pile and ground modeling process, horizontal ground springs are set in the ground at each depth appropriately selected based on the N value set (or estimated) at each depth of the ground, and the ground is modeled. In addition, the nodes P of the piles 40 are appropriately set according to the positions, number, intervals, etc. of the horizontal ground springs set in the ground, and the piles are modeled. 3(b), the pile and ground modeling process includes a shallow ground modeling process (S31) for modeling the shallow ground 111 where the upper part 40A of the pile 40 is located using a shallow N-value, a deep ground modeling process (S32) for modeling the deep ground 113 where the lower part 40B of the pile 40 is located using a deep N-value, and a middle ground modeling process (S33) for modeling the middle ground 115 where the middle part 40C of the pile 40 is located using a middle N-value. In each of steps S31 to S33, the set ground horizontal spring is connected to each node located at the corresponding depth. In this example, the surface layer of the ground is improved in the range of -2.5m from the design ground line, so this area is considered to be shallow ground. The area from the top 2.0m to the bottom 1.0m of the pile tip is considered to be deep ground. The remaining area is considered to be intermediate ground.

[0034] <<Calculation formula for ground horizontal spring K>> Based on the N-values ​​set (or estimated) for each ground, horizontal springs 121 (121a-121e) for the shallow ground, horizontal springs 125 for the middle ground, and horizontal springs 123 (123a-123c) for the deep ground are set at appropriate locations in the shallow ground 111, the middle ground 115, and the deep ground 113. Based on the bending moment and shear force calculated from the set horizontal springs 121-125 for the ground, stress analysis and cross-section inspection of the pile 40 are performed.

[0035] The calculation of the horizontal ground spring K used to model the pile is carried out as follows. In accordance with the architectural foundation structure design guidelines, the horizontal ground reaction coefficient kh (coefficient of horizontal ground reaction) per unit length is calculated using a method similar to Chang's method, and this is multiplied by the pile's visible width and division length to calculate the horizontal ground spring K. The horizontal subgrade reaction coefficient kh is calculated using the following formula. TIFF0007808806000007.tif7150

[0036] however, kh: Coefficient of horizontal subgrade reaction [kN / m3] α: Coefficient determined by the evaluation method ξ: Coefficient that takes into account the effect of pile groups. In this example, which is a single pile, it is 1.0 βk: Liquefaction reduction coefficient. In this example, it is 1.0 E0: Modulus of deformation of the ground [kN / m2]. Estimated as 700 x N value.

[0037] B: Non-dimensional pile diameter (non-dimensional pile diameter expressed in cm, mm) The coefficient α is set to α=60 for clayey soil and α=80 for sandy soil. When safety is a consideration, the coefficient α should be calculated using the smaller value. In this example, the soil type is assumed to be clayey, so the calculation is done using α=60.

[0038] The spring constant K [kN / mm] of the horizontal ground spring is calculated using the following formula. TIFF0007808806000008.tif6150However, h: Burden length [m] B: Pile width (outer diameter of pile body) [m]

[0039] The burden length h of the ground horizontal spring 121 can be from the ground horizontal spring to the adjacent ground horizontal spring below it, or the burden length h of the ground horizontal spring 121 can be a fixed value such as a predetermined length (e.g., 0.5 m) below. Alternatively, the burden length h of the ground horizontal spring may be set from the midpoint between the adjacent ground horizontal spring above to the midpoint between the adjacent ground horizontal spring below. In this case, the burden length of the top ground horizontal spring set to GL=0 is set only below that ground horizontal spring. When calculating the spring, if the horizontal ground spring crosses layers with different horizontal ground reaction coefficients Kh, the horizontal ground reaction coefficient Kh is calculated proportionally according to the control length. The boundary condition at the bottom of the pile in the stress analysis is treated as a pin roller.

[0040] <<Setting interval of ground horizontal spring>> The ground horizontal springs 121-125 set in the ground 111-115 of each layer are set in a quantity and interval that will allow for the analysis results required to consider whether or not to install piles. When a more detailed analysis of the behavior of the piles 40 is required, the ground horizontal springs 121-125 are set at relatively narrow intervals, and when a simple analysis of the behavior of the piles 40 is required, the ground horizontal springs 121-125 are set at relatively wide intervals. The set intervals between the ground horizontal springs 121 to 125 may be constant (for example, L [m]) throughout the entire depth of the ground where the pile 40 is buried. The intervals between the ground horizontal springs 121 to 125 may be changed according to the depth of the ground. The intervals between the ground horizontal springs 121 to 125 may be different for each layer. Since the shallow ground is greatly affected by the stress transmitted from the superstructure and the stress acting on the piles is greatly attenuated by the surface-improved ground, the intervals between the ground horizontal springs in the shallow ground can be shortened to analyze the effect of the stress transmitted from the superstructure in more detail. In this example, the intervals between the ground horizontal springs in the shallow ground are set to 0.5 m (L / 2 [m]), and the intervals between the ground horizontal springs in other areas are set to 1.0 m (L [m]).

[0041] In this design method, the safety of the piles is guaranteed if the average N value of each range of the actual ground is equal to or greater than the N value set for the range of stress bearing length of each ground horizontal spring 121 to 125. However, for the lowest ground horizontal spring 123c, the safety of the pile 40 is guaranteed on the premise that the actual ground also satisfies the average N value in the range of the stress bearing length (for example, L / 2 [m]) borne by the ground horizontal spring 123c from the bottom end of the pile 40 downward.

[0042] <<Step S31: Shallow layer ground modeling process>> The shallow ground 111 shown in Fig. 4 corresponds to the surface layer improvement portion 103 in Fig. 2(f). The design method for the pile 40 according to this embodiment is premised on the assumption that the shallow ground 111 will be subjected to a soil bearing capacity enhancement process by surface layer improvement.

[0043] The surface improvement of the shallow ground 111 is carried out by hardening the ground using concrete, soil cement, cement-based solidifying agent, or other materials. The material used for the surface improvement is selected to be optimal depending on the ground conditions when the shallow part of the ground is excavated during the construction of the piles 40. For example, if the shallow ground 111 is relatively soft and soil cement cannot provide an N-value that generates a spring constant that can sufficiently reduce stress, concrete (ready-mixed concrete) is used to improve the surface layer. When concrete is used, an N-value of approximately 50 can be ensured. For example, if the shallow layer ground 111 can secure an N value of approximately 20 to 30 without using concrete, soil cement is used for improving the surface layer. It is not clear at the time of designing the pile 40 what material will be used for the surface layer improvement. For this reason, at the time of designing the pile 40, an N value that can be reliably guaranteed by carrying out surface layer improvement (for example, N value = 20) is set as the N value of the shallow ground 111, regardless of what kind of improvement is carried out on the shallow ground 111 at the site. It is also possible to set the N value smaller, for example, to N value = 5, in order to design on the safe side.

[0044] The uppermost position of the shallow stratum ground 111 is the upper surface position of the top plate 47 of the pile 40, and this is set as the design GL = 0 (Ground Line = 0). If the length of the rib plates 49, 49... in the direction along the axis Ax is Rh, the shallow stratum ground 111 is set in the range deeper than Rh from GL = 0 and not exceeding twice the length Rh of the rib plates 49, 49... in the direction along the axis Ax. That is, the depth (height) Gd of the shallow stratum ground 111 is set such that Rh < Gd ≦ 2Rh.

[0045] If the shallow stratum ground 111 is set deeper into the ground, there is a possibility that a pile 40 with a smaller diameter, thinner wall, and lower cost can be selected accordingly. However, if a great deal of cost is incurred for surface improvement, the pile 40 cannot be installed at a low cost overall. Therefore, the depth of the shallow stratum ground 111 is ultimately determined based on the balance between the cost related to surface improvement and the cost related to the pile to be installed. As an example, when the length Rh of the rib plates 49, 49... is 1.5 m, the length (depth) Gd of the shallow stratum ground 111 is set to about 2.5 m to 3.0 m.

[0046] In the shallow stratum ground modeling process, at least two shallow stratum ground horizontal springs 121 are set at appropriate positions in the shallow stratum ground 111 at predetermined intervals based on the shallow stratum N - value that can be guaranteed to be ensured in the shallow stratum ground 111 where the upper part 40A of the pile 40 is located, thereby modeling the ground in the shallow stratum. Fig. 4 shows an example in which five ground horizontal springs 121a to 121e are set in the shallow stratum ground 111. In Fig. 5, K1 to K5 correspond to the ground horizontal springs 121a to 121e.

[0047] One of the shallow stratum ground horizontal springs 121 (the shallow stratum ground horizontal spring 121a located at the uppermost position) is arranged in the ground part at the depth where the upper end of the pile 40 is located, that is, at GL = 0. This position is the part where the bending moment M and the shear force Q are directly applied to the pile 40 from the superstructure 10. At least one of the other shallow ground horizontal springs 121 (shallow ground horizontal springs 121d, 121e in the figure) is set at an appropriate location (deeper than the bottom end of the rib plates) between the bottom end of the rib plates 49, 49... and the bottom end of the shallow ground 111. In other words, the shallow ground horizontal springs 121d, 121e are located in a portion of the pile 40 where surface improvement has been performed but no reinforcement by the rib plates 49, 49... is performed, and are placed in a location suitable for cross-sectional testing of the pile 40. This location is important for evaluating whether the pile 40 is within the allowable stress range against the bending moment M and shear force Q damped in the shallow ground 111, even without reinforcement by the rib plates 49, 49... The shallow ground horizontal spring 121e located at the lowest position of the shallow ground 111 can be set to have a burden length up to the lowest position of the shallow ground 111.

[0048] <<Step S32: Deep soil modeling process>> At least two deep ground horizontal springs 123 are set at a predetermined interval in the deep ground 113. Figures 4 and 5 show an example in which three deep ground horizontal springs 123a to 123c are set in the deep ground 113. In Figure 5, K6 to K8 correspond to the ground horizontal springs 123a to 123c.

[0049] One of the deep ground horizontal springs 123 (the deep ground horizontal spring 123c located at the lowest position) is placed in the ground at a depth where the lower end of the pile 40 is located. This position is the part that supports the entire compressive axial force generated by the weight of the superstructure 10, including the weight of the supported object such as the antenna device, and the weight of the pile 40 itself.

[0050] For the deep ground 113, the deep N-value is set to an N-value that allows the piles 40 to exert a strength capable of supporting the compressive axial force generated by the total weight of the superstructure 10, including the weight of supported objects such as antenna devices, and the weight of the piles 40 themselves. The deep N-value must be a value that can maintain the safety of the piles 40 against loads acting in the horizontal direction, in other words, it must not exceed the design target value of the piles.

[0051] If the total weight of the superstructure 10 can be reduced, a relatively small value for the deep N-value will suffice. For example, if the columns 21 of the superstructure 10 are constructed from fiber-reinforced plastic pipes or the like (preferably carbon-fiber-reinforced plastic pipes or the like) and the compressive axial force of the superstructure 10 is limited to 40 kN, then the N-value can be set to 2 as the minimum value capable of supporting this weight. It is also desirable to design the deep ground 113 with a low N-value to be on the safe side. It is not assumed that ground improvement or the like will be carried out on the deep ground 113. However, it has been empirically proven that in a typical region of Japan, no matter how soft the ground may be, if you excavate about 10 to 15 meters, ground with an N value of 2 will appear. The design method according to this embodiment guarantees that piles can be installed in such ground. The range and N value of the deep ground 113 are determined according to the standards and specifications of the piles to be driven, the values ​​required by the piles, etc. As an example, the range and N value of the deep ground 113 can be set as the average N value within a range of 1 Dw below and 1 Dw above the tip of the pile. If the required bearing capacity cannot be obtained with the set N value, or if there are no piles suitable for driving into the ground with that N value, the N value should be set to a larger value.

[0052] <<Step S33: Middle layer ground modeling process>> In the intermediate ground 115, an appropriate number of intermediate ground horizontal springs 125, 125 . . . are set in accordance with the spacing between the horizontal springs 121, 123 set in the shallow ground 111 and the deep ground 113.

[0053] An N value smaller than the N value of the deep ground 113 is set for the middle ground 115. Preferably, an N value of 0 is set as the middle N value for the middle ground 115. In this case, stress analysis is performed assuming that the spring constant K of the middle ground horizontal springs 125, 125... is zero. In FIG. 5, illustration of the ground horizontal springs connected to the pile nodes P6 to P11 is omitted as an example where the N value of the middle ground 115 is 0 and the spring constant K is 0.

[0054] Here, stresses such as bending moment and shear force transmitted from the upper structure 10, which is swaying due to strong winds or the like, to the piles 40 decrease monotonically toward the tip of the piles 40, whether the N value of the middle ground 115 is set to 0 or to 1 or more. The magnitude of the N value set for the middle ground 115 changes the attenuation rate of the stress. Stress is transmitted from the upper structure 10 to the piles 40, but the shallow ground 111 that has undergone surface improvement is very resistant to deformation, and the stress can be sufficiently reduced. For this reason, even if the N-value of the middle ground 115 is set to 0, no numerical value that will adversely affect the cross-sectional inspection of the piles 40 will be calculated. In this way, the magnitude of the N-value set for the middle ground 115 becomes less significant as a value for considering the effect that stress transmitted from above has on the piles 40. It is not assumed that ground improvement or the like will be carried out on the middle ground 115. If the actual ground is soft, the N-value of the middle ground may be very low, but if the N-value of the middle ground is set to zero at the design stage, it is possible to accommodate areas where the actual N-value of the middle ground is very low. If the actual deep ground has the N-value set for the modeled deep ground, it is guaranteed that the piles 40 designed by this design method can be installed even in soft ground where the N-values ​​of the shallow and middle ground are relatively small.

[0055] <Step S4: Stress analysis process> <<Stress analysis software>> Stress analysis calculates the horizontal behavior of the pile. The stress analysis of piles is a plane static elastic analysis. For the stress analysis, for example, the stress analysis software "SNAP" by Structural Systems Co., Ltd. can be used. Programs related to stress analysis are installed and used on a computer equipped with a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), HDD (Hard Disk Drive), a keyboard and mouse as input means, a display as display means, etc. The CPU reads the program stored on the HDD, expands it into RAM, and executes the control program using the RAM as a workspace, allowing the computer to function as a stress analysis device and realize the various functions required for stress analysis on the computer.

[0056] <<Value to be entered>> When the piles and superstructure are directly connected with flanges, the foundation weight is zero, so the story shear force acting on the superstructure acts directly on the pile head. Therefore, the stress acting on the lowest point of the superstructure (bending moment M and shear force Q) is input to the pile head. Necessary data is input into the stress analysis software, such as the spring constant K of the horizontal spring at each depth in the ground, the pile diameter, thickness, corrosion allowance, and steel material (standard design strength of steel).The stress analysis calculates the stress state (bending moment M, shear force Q, deformation amount, rotation amount, etc.) at each node of the modeled pile.

[0057] <<Stress analysis results>> Figure 6 shows an example of the stress analysis results, where (a) is a moment diagram and (b) is a shear force diagram. This figure shows the analysis results during a very rare storm. As shown in Figure 6(a), the bending moment monotonically decreases in the middle ground 115 where the N value is 0, and it can be seen that if the stress applied to the pile head from the superstructure is sufficiently reduced in the shallow ground, the condition of the middle ground does not affect the bending strength of the pile.

[0058] <Step S5: Pile inspection process> The provisionally selected piles are inspected to see if they meet the design target values. That is, it is examined whether the vertical axial force acting on the pile under each of the conditions of long-term, earthquake, and wind load is within the range of the bearing capacity of the pile calculated in step S2. Under each of the above conditions, the horizontal forces acting on the pile (bending moment (existing stress), existing stress on the compression side and tension side, shear stress) are examined to see if they are within the range of the allowable strength and allowable stress of the pile calculated in step S2. If the stresses acting on the pile are within the range of the pile's bearing capacity and allowable stress level, the provisionally selected pile is selected as a usable pile (OK in step S5). If the stresses acting on the pile exceed the bearing capacity and allowable stress of the pile (NG in step S5), return to step S1 and provisionally select another pile. Alternatively, a larger N value can be set in step S3.

[0059] 〔effect〕 In this embodiment, by adopting a design method that assumes surface improvement, pile design can be carried out regardless of the region where the piles are planned to be installed (within Japan or outside Japan), even in areas where ground investigation data cannot be obtained at the design stage. In other words, when modeling the ground, an N-value that can be reliably secured through surface improvement is set for shallow ground, and the minimum N-value that can support the weight of the superstructure and piles is set for deep ground. By doing this, even if an N-value of 0 is set for the middle ground, in other words, no matter what N-value the ground layer where the middle part of the pile is located in the axial direction has, it is guaranteed that there will be no problem with the pile's bearing capacity. Therefore, even without the results of a soil survey, it is possible to proceed with the design of piles that can be installed regardless of the ground conditions.

[0060] Furthermore, even if the N-value of the location where the pile will be installed is unknown at the time of pile design, if the N-value is later determined through a ground survey, the stress can be recalculated based on the measured N-value and the pile re-tested, and a pile with a diameter or axial length different from the original design can be selected as the pile to be actually installed. In either case, setting the N value to a smaller value (on the safe side) at the time of design will enable safer pile design.

[0061] In this way, it is possible to proceed with pile design even in areas where soil survey results cannot be obtained in advance, making it possible to determine early on whether or not a tower-like structure can be constructed, taking into account the exclusive land area required for the construction of the tower-like structure, whether or not the land can be leased, etc.

[0062] [Application to pile groups] Figure 7 is a schematic front view showing a pile to be designed according to another embodiment of the present invention and a part of the superstructure supported by the pile. This figure also shows a horizontal ground spring to be set in the ground. The above-mentioned pile design method can also be applied to pile groups. The illustrated substructure 60 is configured to include a footing 61 and a plurality of piles 40. The footing 61 includes an anchor frame 63 embedded therein and a plurality of anchor bolts 65 extending upright from the anchor frame 63. The substructure 60 is integrated with the base plate 13 of the superstructure 10 via the anchor bolts 65 protruding above ground level and nuts 67. As an example, the footing 61 is formed into a rectangular shape in a plan view, and piles 40 can be placed at each of the four corners of the footing 61. As a result, the superstructure 10 is supported by the multiple piles 40 via the footing 61. The piles 40 and the footing 61 can be integrated by embedding the upper ends of the piles 40 into the footing by a predetermined length. Alternatively, the piles 40 and the footing 61 can be integrated by flare-welding multiple pile head reinforcements 69 to the upper ends of the piles 40 along the circumferential direction of the piles 40, thereby fixing the pile head reinforcements into the footing 61.

[0063] When the piles 40 are connected to the superstructure 10 via footings 61, the design can be such that the stresses (bending moment and shear force = base shear) transmitted from the superstructure due to the respective inertial forces during earthquakes and wind loads are borne by the footings 61. By adopting this design method, the piles 40 can be designed to bear mainly the long-term axial force and the horizontal forces generated during earthquakes and wind loads. In other words, even in the case of a group of piles, the piles themselves can be designed in the same way as a single pile.

[0064] In the case of pile groups, since a footing exists, it is assumed that no surface improvement work will be carried out on the shallow ground 111 where the heads of the piles are located. Therefore, the shallow ground 111 can be set to the minimum N value (for example, N value = 2) that should be possessed when constructing a tower-like structure. For the deep ground 113, an N-value is set so that each pile can share and demonstrate the bearing capacity required to support the compressive axial force generated by the weight of the superstructure 10, the weight of the footing 61, and the weight of the piles 40, 40... However, since the pile diameter of each pile in a group pile is smaller than that of a single pile, a larger N-value is required for the part of the ground where the tip of each pile is located. For example, the N-value of the deep ground 113 is set to 10. The middle ground 115 can be set to an N value (for example, N value = 0) that is smaller than both the shallow ground 111 and the deep ground 113. In the case of pile groups, it is also possible to adopt a design method that does not set the middle ground. In other words, the entire part corresponding to the middle ground can be treated as being included in the shallow ground. The total axial length of the pile 40 is set to a length at which the tip of the pile is positioned at a depth that is empirically considered to be able to ensure the N value required for the deep ground 113 . One of the shallow ground horizontal springs 121a is set at the boundary position with the footing 61, i.e., at the bottom surface of the footing. The other ground horizontal springs 121b, 121c are set in such a number and at such an interval that the analysis results necessary for examining whether or not piles can be installed can be obtained. If more detailed data on the stress state is required, the interval between the ground horizontal springs is set shorter.

[0065] In the stress analysis process of step S4 in Figure 3(a), the burden shear force and bending moment generated in each pile 40, 40... are calculated from the shear force (base shear Qb) generated at the lowest point of the superstructure 10 and the overturning moment M. In the verification process of step S5, it is verified whether the allowable strength (short-term allowable stress, ultimate strength) of each pile exceeds the above stress. In this way, the basic concept of the design method of the present invention can also be applied to pile groups.

[0066] [Application to other types of piles] The present invention has been specifically described above based on the preferred embodiment, but the present invention can adopt the following modifications. The design method according to the present invention can also be applied to other types of piles such as steel piles, wooden piles, precast concrete piles, and cast-in-place concrete piles. The design method according to the present invention can also be applied to piles having shapes that do not have tip wings 43, 43. For example, it can be applied to straight piles that have a constant outer diameter (external shape) over the entire axial length, expanded base piles in which the tip of the pile is expanded into a conical shape, etc., and expanded head piles in which the diameter of the head of the pile is expanded. In the case of straight piles or enlarged head piles, the N-value required for deep soil may be higher. In this case, either increase the total axial length of the pile to ensure the required N-value, or select another type of pile.

[0067] [Summary of Examples of Embodiments, Actions, and Effects of the Present Invention] <First embodiment> The pile design method according to this embodiment is a method for designing a pile 40, which is a single pile that is driven into the ground 100 and supports a superstructure 10 joined to the top thereof. This design method includes a shallow ground modeling process (S31) in which at least two shallow ground horizontal springs 121 are set at appropriate locations in the shallow ground at predetermined intervals based on the shallow N-value that can be secured in the shallow ground 111 where the upper part 40A of the pile is located, thereby modeling the shallow ground; a deep ground modeling process (S32) in which at least two deep ground horizontal springs 123 are set at appropriate locations in the deep ground at predetermined intervals based on the deep N-value required for the deep ground 113 where the lower part 40B of the pile is located, thereby modeling the deep ground; and a middle ground modeling process (S33) in which N-value = 0 is set for the middle ground 115 where the middle part 40C of the pile is located, and one or more middle ground horizontal springs 125 are set at appropriate locations in the middle ground at predetermined intervals, thereby modeling the middle ground. Furthermore, this design method includes a stress analysis process (S4) for analyzing the stress state of the pile when bending moment and shear force are applied to the pile head from the superstructure, and a testing process (S5) for testing whether the pile can withstand the stress state. In this design method, the shallow ground is set to the depth range of the ground where surface improvement is planned, and the N value of the shallow ground is set to the N value obtained by surface improvement.

[0068] According to this aspect, piles can be designed even without ground investigation data. In other words, even if a large stress is applied to the pile head from the superstructure, if the N-value of the shallow ground can be increased, this stress will be sufficiently attenuated within the shallow ground. Therefore, in this embodiment, assuming that the shallow ground will be subjected to surface improvement, an N-value that can be reliably secured by surface improvement is set for the shallow ground. For deep ground, the N-value that the deep ground should have is set as the deep N-value. The deep N-value is the N-value that can demonstrate the strength to support the compressive axial force generated by, for example, the total weight of the superstructure and the weight of the piles. Set the N value to 0 for the middle layer of the ground. Whatever N value is set for the middle layer of the ground, the magnitude of the stress transmitted based on the deformation of the superstructure monotonically decreases as you go down the pile. If the stress applied to the pile head is sufficiently attenuated in the shallow layer of the ground, the middle and below of the pile will be able to satisfy the allowable stress related to shear force, so there is no problem in design even if the N value is set to 0. Furthermore, setting the N value to 0 will result in setting an N value smaller than the actual ground, allowing the pile to be designed on the safe side.

[0069] <Second embodiment> In the pile design method according to this embodiment, the pile 40 comprises a hollow cylindrical pile body 41 extending vertically, and a plurality of reinforcing rib plates 49, 49... that protrude radially outward from the upper end of the pile body and whose protrusion amount gradually decreases toward the bottom of the pile, and the shallow ground 111 is set to a depth range in which at least the entirety of each rib plate is buried. According to this embodiment, it is assumed that the stress transmitted from the superstructure 10 is attenuated in the rib plate and the surface-improved surface layer improved portion 103 (shallow ground 111). Therefore, even if the N value of the middle layer is set to 0, the piles can be designed without any problems.

[0070] <Third embodiment> In the pile design method according to this embodiment, one of the shallow ground horizontal springs 121 (shallow ground horizontal spring 121c) set in the shallow ground 111 is characterized in that it is positioned deeper than the lower ends of the rib plates 49, 49...

[0071] In this embodiment, even in the pile portion where reinforcement by the rib plates 49, 49... is no longer present, one of the shallow ground horizontal springs is placed deeper than the lower end of the rib plate as an important location for evaluating whether the pile 40 (pile body 41) is within the allowable stress range.

[0072] <Fourth embodiment> In the pile design method of this embodiment, the deep layer N value is set to an N value that can withstand the compressive axial force generated by the total weight of the superstructure 10 and the weight of the pile 40 itself, and the total axial length of the pile is set so that the lower end of the pile reaches a depth in the ground 100 at which the deep layer N value can appear. The deep N-value that the deep soil should have can be determined based on the total weight of the superstructure and the weight of the pile. Once the deep N-value can be determined, it is possible to empirically determine the depth at which the soil with that N-value appears. Therefore, the total axial length of the pile can be determined. In other words, piles can be designed even without soil survey data. Here, if the superstructure can be made lighter, the compressive axial force will be reduced, and the required deep N-value will be relatively small. In other words, depending on the total weight of the superstructure, the applicable area of ​​this design method can be expanded.

[0073] <Fifth embodiment> In the pile design method according to this embodiment, the pile 40 is a rotary penetration type steel pipe pile having tip wings 43, 43 that have a screwing action into the ground. Piles with tip wings can increase the bearing resistance exerted by the tip of the pile, so that even in ground with a relatively low N-value, the superstructure can be supported without relying solely on the frictional resistance of the pile periphery. Therefore, the pile design method according to the embodiment of the present invention makes it possible to design piles without assuming that the tip of the pile will reach a supporting layer such as bedrock, thereby expanding the area in which the design method according to this embodiment can be applied. In this embodiment, it is easy to predict the total length of the pile to be installed.

[0074] <Sixth embodiment> The pile design method according to this embodiment is a method for designing piles 40, 40 . . . that are driven into the ground 100 and support the superstructure 10 connected via a footing 61. This design method includes a shallow ground modeling step (S31) in which at least two shallow ground horizontal springs 121 are set at appropriate locations in the shallow ground at predetermined intervals based on the minimum shallow N-value that the shallow ground 111 where the top of the pile is located must have in order to support the superstructure, thereby modeling the shallow ground; a deep ground modeling step (S32) in which at least two deep ground horizontal springs 123 are set at appropriate locations in the deep ground at predetermined intervals based on the deep N-value required for the deep ground 113 where the bottom of the pile is located, thereby modeling the deep ground; and a middle ground modeling step (S33) in which the N-value = 0 is set for the middle ground 115 where the middle part of the pile is located, and one or more middle ground horizontal springs 125 are set at appropriate locations in the middle ground at predetermined intervals, thereby modeling the middle ground. Furthermore, this design method is characterized by including a stress analysis process (S4) for analyzing the stress state of the pile when bending moment and shear force are applied from the footing to the top of the pile, and a testing process (S5) for testing whether the pile can withstand the stress state. According to this aspect, similar to the first embodiment, piles can be designed even without ground investigation data. [Explanation of symbols]

[0075] Ax...axis (of pile, pile body, and superstructure), 10...superstructure, 11...base, 13...base plate, 15...tapered steel pipe, 17...reinforcing rib, 21...support, 30...joint plate, 40...pile (substructure), 40A...upper part, 40B...lower part, 40C...middle part, 41...pile body, 43...tip wing, 45...digging blade, 47...top plate, 49...rib plate, 51...lower member (lower end of pile), 53...upper member (upper end of pile), 55...intermediate member (middle part of pile), 60...substructure, 61...footing, 63...anchor frame, 65...anchor bolt, 67...nut, 69...pile head reinforcement, 100...ground, 101...work pit, 103...surface improvement part, 111...shallow ground, 113...deep ground, 115...middle ground, 121, 121a to 121e...shallow ground horizontal spring, 123, 123a to 123c...deep ground horizontal spring, 125...middle ground horizontal spring, F1 to F3...fastening member

Claims

1. A method for designing a single pile that is driven into the ground and supports a superstructure connected to the top, comprising: a shallow layer ground modeling process in which at least two shallow layer ground horizontal springs are set at appropriate locations in the shallow layer ground at predetermined intervals based on the shallow layer N value that can be secured in the shallow layer ground where the upper part of the pile is located, and the shallow layer ground is modeled; A deep ground modeling process in which at least two deep ground horizontal springs are set at appropriate locations in the deep ground at predetermined intervals based on the deep ground N value required for the deep ground where the bottom of the pile is located, and the deep ground is modeled; a middle layer ground modeling step of setting an N value of 0 in the middle layer ground where the intermediate portion of the pile is located, and setting one or more middle layer ground horizontal springs at predetermined intervals in appropriate locations within the middle layer ground to model the middle layer ground; a stress analysis step of analyzing the stress state of the pile when a bending moment and a shear force are applied to the pile head from the superstructure; and a testing step of testing whether the pile can withstand the stress state, A pile design method characterized in that the shallow ground is set to the depth range of the ground where surface improvement is planned, and the shallow N-value is set to the N-value obtained by the surface improvement.

2. The pile comprises a hollow cylindrical pile body extending in the vertical direction, and a plurality of reinforcing rib plates protruding radially outward from the upper end of the pile body, the protruding amount gradually decreasing toward the bottom of the pile; 2. The pile design method according to claim 1, wherein the shallow layer of ground is set to a depth range in which at least the entirety of each of the rib plates is buried.

3. 3. The pile design method according to claim 2, wherein at least one of the shallow ground horizontal springs set in the shallow ground is positioned deeper than the lower end of the rib plate.

4. The deep layer N value is set to an N value that can withstand the compressive axial force generated by the total weight of the superstructure and the weight of the pile, A pile design method as described in any one of claims 1 to 3, characterized in that the total axial length of the pile is set so that the lower end of the pile reaches a depth in the ground at which the deep N value can appear.

5. 5. The pile design method according to claim 4, wherein the pile is a rotary penetration type steel pipe pile having tip blades that have a screwing action into the ground.

6. A design method for piles that are driven into the ground and support a superstructure connected via a footing, comprising: a shallow ground modeling step of setting at least two shallow ground horizontal springs at predetermined intervals in appropriate locations within the shallow ground based on the minimum shallow ground N value that the shallow ground where the upper part of the pile is located should have in order to support the superstructure, and modeling the shallow ground; A deep ground modeling process in which at least two deep ground horizontal springs are set at appropriate locations in the deep ground at predetermined intervals based on the deep ground N value required for the deep ground where the bottom of the pile is located, and the deep ground is modeled; a middle layer ground modeling step of setting an N value of 0 in the middle layer ground where the intermediate portion of the pile is located, and setting one or more middle layer ground horizontal springs at predetermined intervals in appropriate locations within the middle layer ground to model the middle layer ground; a stress analysis step of analyzing the stress state of the pile when a bending moment and a shear force are applied from the footing to the upper part of the pile; and a testing step of testing whether the pile can withstand the stress state.

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