Method for estimating peripheral resistance and method for estimating compressive resistance for designing pile with at least tapered tip, pile design method, and pile

Abstract

To provide a method for estimating peripheral resistance and a method for estimating compressive resistance for designing tapered piles.SOLUTION: A method for estimating peripheral resistance force or a method for estimating compressive resistance force includes a step of using a sampler (140) having a first shoe cone (150) attached to a tip of a rod (110) to obtain the number of strikes required to drive the sampler a predetermined length as a measurement value A, and estimating peripheral resistance force (Rf) using the measurement value A, where the first shoe cone is a shoe cone with a tapered tip.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for estimating a surface resistance force and a method for estimating a compressive resistance force for designing a pile having at least a tapered tip portion, a pile design method, and a pile. [Background technology]

[0002] Steel pipe piles are used as foundations for a variety of structures and are driven into the ground or underwater. Because the resistance of steel pipe piles varies depending on the shape of the steel pipe pile and the strength of the ground, standard penetration tests were conducted in accordance with the standard penetration test method specified in the Japanese Industrial Standards (JIS A 1219:2013) to determine the N-value, which indicates the strength of the ground.

[0003] Once the N-value is calculated, it is possible to calculate the tip resistance, skin resistance, and compressive resistance. Once the compressive resistance corresponding to the ground into which the steel pipe pile will be driven is calculated, it becomes possible to determine how to design the steel pipe pile according to the conditions required for the steel pipe pile by the structure on which it is based.

[0004] The design of steel pipe piles based on the above-mentioned compressive resistance applies mainly to steel pipe piles known as straight piles. In recent years, tapered piles have begun to be used, which have advantages such as the ability to shorten the pile length due to a higher circumferential resistance than straight piles (see, for example, Patent Document 1). Note that a straight pile refers to an open-end pile whose external shape does not change from the tip to the head, while a tapered pile refers to a steel pipe pile that has a straight section similar to a straight pile and a tapered section at the tip, and a steel pipe pile that is tapered along its entire length. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2019-78032 Summary of the Invention [Problem to be solved by the invention]

[0006] However, since the circumferential resistance or compressive resistance calculated based on the above-mentioned N value is for straight piles, applying the same method to tapered piles would not allow for an accurate estimation of the expansion effect, which is a characteristic of tapered piles, and therefore there was a need for a method of estimating circumferential resistance and compressive resistance for designing tapered piles.

[0007] An object of the present invention is to provide a method for estimating skin resistance and a method for estimating compressive resistance for designing tapered piles. [Means for solving the problem]

[0008] The method for estimating skin resistance according to the present invention includes a step of using at least one of a sampler having a first shoe cone attached to the tip of a rod and a sampler having a third shoe cone attached to the tip of a rod, obtaining the number of blows required to drive the sampler a predetermined length as a measurement value A, and estimating skin resistance using the measurement value A, wherein the first shoe cone is a shoe cone with at least the tip tapered, and the third shoe cone is a shoe cone whose pile outer shape does not change from the tip to the head of the pile.

[0009] In the method for estimating peripheral resistance force according to the present invention, it is preferable that the first shoe cone includes a cylindrical straight portion on the side that is connected to the rod, and a tapered portion that is connected to the straight portion and has a side surface that narrows in diameter at a predetermined taper angle in the direction of the central axis of the first shoe cone.

[0010] The method for estimating indentation resistance force according to the present invention includes the steps of using at least one of a sampler having a first shoe cone attached to the tip of a rod and a sampler having a third shoe cone attached to the tip of a rod, obtaining the number of blows required to drive the sampler a predetermined length as measurement value A, using a sampler having a second shoe cone attached to the tip of a rod, obtaining the number of blows required to drive the sampler a predetermined length as measurement value B, estimating the circumferential resistance force using measurement value A, estimating the tip resistance force using measurement value B, and estimating the indentation resistance force based on the estimated tip resistance force and the estimated circumferential resistance force, wherein the first shoe cone is a shoe cone with at least the tip tapered, and the third shoe cone is a shoe cone whose pile outer shape does not change from the tip to the head of the pile.

[0011] In the method for estimating indentation resistance force according to the present invention, it is preferable that the first shoe cone includes a cylindrical straight portion on the side that is connected to the rod, and a tapered portion that is connected to the straight portion and has a side surface that narrows in diameter at a predetermined taper angle in the central axis direction of the first shoe cone.

[0012] In the method for estimating indentation resistance force according to the present invention, the second shoe cone preferably has a different shape from the first shoe cone and the third shoe cone.

[0013] The pile design method of the present invention is a pile design method that estimates the skin resistance of a pile with at least the tip portion tapered, estimates the pile's push-in resistance, and designs a steel pipe pile based on the skin resistance and push-in resistance.The process of estimating the skin resistance includes a step of using at least one of a sampler with a first shoe cone attached to the tip of a rod and a sampler with a third shoe cone attached to the tip of a rod, obtaining the number of blows required to drive the sampler a predetermined length as a measurement value A, and using the measurement value A to estimate the skin resistance.The first shoe cone is a shoe cone with a tapered tip, and the third shoe cone is a shoe cone whose outer shape does not change from the tip of the pile to the head of the pile.

[0014] The pile design method of the present invention is a pile design method that estimates the skin resistance of a pile whose tip portion is tapered, estimates the compressive resistance of the pile, and designs the pile based on the skin resistance and compressive resistance. The process of estimating the compressive resistance includes the steps of: using a sampler with a first shoe cone attached to the tip of a rod, obtaining as measurement value A the number of blows required to drive the sampler a predetermined length; using at least one of a sampler with a second shoe cone attached to the tip of a rod and a sampler with a third shoe cone attached to the tip of a rod, obtaining as measurement value B the number of blows required to drive the sampler a predetermined length; estimating the skin resistance using measurement value A; estimating the tip resistance using measurement value B; and estimating the compressive resistance based on the estimated tip resistance and the estimated skin resistance. The first shoe cone is a shoe cone whose tip portion is tapered, and the third shoe cone is a shoe cone whose outer shape does not change from the tip to the head of the pile.

[0015] The pile of the present invention is a pile that estimates the skin resistance of a pile with at least the tip portion tapered, estimates the pushing resistance of the pile, and is designed based on the skin resistance and pushing resistance.The process of estimating the skin resistance includes a step of using at least one of a sampler with a first shoe cone attached to the tip of a rod and a sampler with a third shoe cone attached to the tip of a rod, obtaining the number of blows required to drive the sampler a predetermined length as a measurement value A, and using the measurement value A to estimate the skin resistance.The first shoe cone is a shoe cone with a tapered tip, and the third shoe cone is a shoe cone whose outer shape does not change from the tip to the head of the pile.

[0016] The pile according to the present invention is a pile that estimates the skin resistance of a pile having at least a tapered tip, estimates the indentation resistance of the pile, and is designed based on the skin resistance and the indentation resistance. The process of estimating the indentation resistance includes the steps of: using at least one of a sampler having a first shoe cone attached to the tip of a rod and a sampler having a third shoe cone attached to the tip of a rod, obtaining the number of blows required to drive the sampler a predetermined length as measurement value A; using a sampler having a second shoe cone attached to the tip of a rod, obtaining the number of blows required to drive the sampler a predetermined length as measurement value B; estimating the skin resistance using measurement value A; estimating the tip resistance using measurement value B; and estimating the indentation resistance based on the estimated tip resistance and the estimated skin resistance. The first shoe cone is a shoe cone having a tapered tip, and the third shoe cone is a shoe cone whose outer shape does not change from the tip to the head of the pile. [Effects of the Invention]

[0017] The estimation method according to the present invention makes it possible to provide a method for estimating skin resistance and a method for estimating compressive resistance for designing tapered piles. [Brief explanation of the drawings]

[0018] [Figure 1] A diagram showing an example of the procedure for designing tapered piles. [Figure 2] FIG. 2 is a diagram showing the external shape of the tapered pile 10. [Figure 3] FIG. 10 is a diagram showing a procedure for obtaining measurement values A and B. [Figure 4] 4(a) to 4(c) are diagrams for explaining the procedure of FIG. [Figure 5] 4(a) to 4(c) are diagrams for explaining the procedure of FIG. [Figure 6] 1(a) shows a JIS type shoe cone 20, and FIG. 1(b) shows a tapered shoe cone 30. FIG. [Figure 7] This is a diagram showing an example of a soil log (1-30m). [Figure 8] This is a diagram showing an example of a soil log (31-50m). [Figure 9] This is a diagram showing an example of a soil log (51-75m). [Figure 10] 10(a) to 10(d) are diagrams showing calculation formulas for calculating the peripheral friction force fs and the ultimate tip support qd from the N value and the T value. [Figure 11] (a) is a diagram showing a design example of a straight pile, (b) and (c) are diagrams showing design examples of a tapered pile, and (d) is a diagram showing an example of a soil column diagram referenced to design (a) to (c). [Figure 12] FIG. 1(a) is a schematic diagram of the test equipment used in the small-scale dynamic penetration test according to the embodiment, and FIG. 1(b) is a diagram showing the model ground used in the small-scale dynamic penetration test. [Figure 13] FIG. 12(a) is a diagram showing samplers according to Comparative Examples 1 to 3 and Examples 1 to 5 attached to the tip of the rod shown in FIG. [Figure 14] FIG. 12(a) is a diagram showing the change in the number of blows Nd until the samplers according to Comparative Examples 1 and 2 and Examples 1 and 2 penetrate into the model ground to a position 300 mm from the upper surface of the lower part of the model ground shown in FIG. 12(a). [Figure 15] 12(a) is a diagram showing the change in the tip load applied to the rod while the samplers according to Comparative Examples 1 and 2 and Examples 1 and 2 are inserted into the model ground to a position 300 mm from the upper surface of the lower part of the model ground shown in FIG. 12(a), and FIG. 12(b) is a diagram showing the tip load applied to the rod when the samplers according to Comparative Examples 1 to 3 and Examples 1 to 5 are inserted to a position approximately 300 mm from the upper surface of the lower part of the model ground shown in FIG. 12(a). [Figure 16] (a) is a diagram showing the straight pile used to measure measurement value B, and (b) is a diagram showing the tapered pile used to measure measurement value A. [Figure 17] FIG. 10 shows the transition of measurement values A and B with the change in the depth of penetration of the sampler. [Figure 18](a) is a diagram showing the change in depth with each blow when a straight pile is installed in a layer approximately 13 m deep, and (b) is a diagram showing the change in depth with each blow when a tapered pile is installed in a layer approximately 14 m deep. DETAILED DESCRIPTION OF THE INVENTION

[0019] Various embodiments of the present invention will be described below with reference to the drawings. Please note that the technical scope of the present invention is not limited to these embodiments, but extends to the inventions described in the claims and their equivalents.

[0020] FIG. 1 is a diagram showing an example of a procedure for designing a tapered pile.

[0021] The procedure for designing tapered piles begins with conducting a test similar to the standard penetration test method (JIS A 1219:2013) for estimating the compressive resistance of straight piles, and obtaining measurement values A and B (S10). The method for obtaining measurement values A and B will be described later.

[0022] Next, a soil columnar diagram of the soil where the tapered pile will be placed is created based on the measurement values A and B obtained in S10 (S11), and the compressive resistance R (kN) of the tapered pile to be designed is estimated based on the measurement values A and B obtained in S10 and the soil columnar diagram created in S11 (S12). The compressive resistance R can be expressed as the sum of the skin resistance Rf (kN) and the tip resistance Rp (kN). The present invention relates to a skin resistance estimation method for estimating the skin resistance Rf and a compressive resistance estimation method for estimating the compressive resistance R.

[0023] Next, the action on the pile head is calculated based on the loading conditions on the tapered pile to be designed, the foundation shape of the building etc. that the tapered pile to be designed will support, the arrangement of the tapered pile to be designed, and the specifications of the tapered pile to be designed (S13).

[0024] Finally, the tapered pile is designed based on the compressive resistance force R estimated in S12 and the action on the pile head calculated in S13 (S14), completing the procedure for designing the tapered pile.

[0025] FIG. 2 is a diagram showing the outer shape of the tapered pile 10. As shown in FIG.

[0026] The tapered pile 10 is defined by a straight portion p1 (m), a tapered portion p2 (m), a taper angle pθ (°), a pile tip diameter p3 (m), and a pile head diameter p4 (m). That is, in the procedure for designing the tapered pile shown in FIG. 1, the five parameters (p1, p2, p3, p4, pθ) are determined in S14. Note that although the tapered pile 10 has a straight portion p1, the present invention is applicable to any tapered pile in which at least the tip portion is tapered, and is also applicable to tapered piles that do not have a straight portion and are tapered along their entire length.

[0027] Fig. 3 is a diagram showing the procedure for acquiring measurement value A and measurement value B in S10 of Fig. 1, and Figs. 4 and 5 are diagrams for explaining the procedure of Fig. 3. In order to create a soil columnar diagram of the soil type described in S11 of Fig. 1, it is necessary to measure measurement value A for estimating skin resistance Rf and measurement value B for estimating tip resistance Rp at predetermined depths (for example, every 1 m) (specific examples will be described later). However, Figs. 3 to 5 show the procedure for measuring measurement value A once and measurement value B once.

[0028] In the procedure for measuring the measurement values, the first preparation step is carried out (S20). Figure 4(a) is a diagram corresponding to the first preparation step. As shown in Figure 4(a), the penetration test device 100 is placed at the planned placement location of the tapered pile 10.

[0029] The penetration test device 100 includes a boring machine 101, an anvil 102, a hammer 103, a guide rod 104, an automatic drop device 105, a pulley 106, a tower 107, a hoisting rope 108, a cone pulley 109, and the like.

[0030] Next, the test hole is excavated using the installed penetration test device 100 (S21). Figure 4(b) is a diagram corresponding to the test hole excavation. As shown in Figure 4(b), a rod 110 is rotated using a boring machine 101 to excavate a test hole of a predetermined depth. A mouth pipe 111 is placed at the top of the test hole, and a driving pipe 112 is placed inside the test hole.

[0031] Next, the sampler 140 is positioned using the positioned penetration test device 100 (S22). Figure 4(c) is a diagram corresponding to the positioning of the sampler 140. As shown in Figure 4(c), once the test hole 130 of the predetermined depth has been excavated, the tip of the sampler 140, which has a first shoe cone 150 attached to the tip of the rod 110, is positioned at the bottom of the test hole 130. The first shoe cone 150 will be described later.

[0032] Next, it is observed whether the first shoe cone 150 sinks by itself (S23), and if it does sink by itself, the amount of sinking is recorded (S24). Note that "sinking by itself" means that when the first shoe cone 150 is placed at the bottom of the test hole 130, it penetrates without the hammer 103 falling.

[0033] Next, preliminary driving is performed using the installed penetration test apparatus 100 (S25). Figure 5(a) is a diagram corresponding to the preliminary driving. Note that for convenience of explanation, Figure 5(a) does not show the entire penetration test apparatus 100, but only shows the anvil 102, hammer 103, and automatic drop device 105. In the preliminary driving, the first shoe cone 150 is penetrated from the bottom of the test hole 130 to a predetermined distance (e.g., 150 mm), including the amount of self-sinking, by the impact of the hammer 103 by the automatic drop device 105. Note that the preliminary driving (S25) may be omitted. For example, in extremely dense ground, the tip of the shoe cone becomes significantly blocked during penetration even at the preliminary driving stage. Therefore, if such ground is expected, the main driving (S26) may be performed directly from the test start depth without preliminary driving.

[0034] Next, the penetration test device 100 is used to perform the actual hitting (S26), and the number of hits of the hammer 103 during that time is acquired as a measured value A (S27). Figure 5(b) is a diagram corresponding to the actual hitting and acquisition of the measured value A. Note that, for convenience of explanation, Figure 5(b) does not show the entire penetration test device 100, but shows only the anvil 102, hammer 103, and automatic drop device 105.

[0035] In the actual hitting, the hammer 103 is hit by the automatic drop device 105 until the first shoe cone 150 penetrates 300 mm from the position of the preliminary hitting (S25), and the number of hits during that time is acquired as a measurement value A (S26). The automatic drop device 105 is configured to allow the hammer 103 to freely fall from a predetermined distance (for example, 760 mm).

[0036] Thereafter, the sampler, which is the test device 140, is collected (S28), completing the procedure for obtaining the measured value A. Fig. 5(c) is a diagram corresponding to the collection of the sampler.

[0037] Next, the first shoe cone 150 is replaced with the second shoe cone 160, and steps S29 to S37, which are similar to steps S20 to S28, are carried out to obtain a measurement value B. S29 to S37 are the same steps as steps S20 to S28 except that the second shoe cone 160 is attached to the tip of the rod 110 and the measurement value obtained is measurement value B, so a description of these steps will be omitted. The second shoe cone 160 will be described later.

[0038] FIG. 6 is a diagram showing an example of a shoe cone.

[0039] Figure 6(a) shows a JIS-type shoe cone 20 specified in the Standard Penetration Test Method (JIS A 1219:2013). According to the Standard Penetration Test Method (JIS A 1219:2013), by using the JIS-type shoe cone 20 shown in Figure 6(a) as the second shoe cone 160 described in steps S29 to S37 shown in Figure 3, it is possible to obtain the N-value specified in the Standard Penetration Test Method (JIS A 1219:2013) as the measurement value B.

[0040] FIG. 6(b) shows a tapered shoe cone 30 designed for tapered piles. The tapered shoe cone 30 designed for tapered piles is defined by a straight section s1 (mm), a tapered section s2 (mm), a taper angle sθ (°), a tip pile diameter s3 (mm), and a pile head diameter s4 (mm). The cylindrical straight section s1 is connected to the rod 110, and the tapered section s2 is connected to the straight section s1 and has a side surface that narrows in diameter at a predetermined taper angle sθ in the direction of the central axis of the shoe cone 30. The diameter of the opening formed at the tip of the tapered section s2, which is perpendicular to the central axis, is the tip pile diameter s3. For example, s1 = 56 (mm), s2 = 150 (mm), s3 = 20 (mm), s4 = 51 (mm), and sθ = 5°. Note that although the tapered shoe cone 30 shown in FIG. 6(b) has an opening, a tapered shoe cone without an opening can also be used.

[0041] The following three methods are conceivable as methods for estimating the indentation resistance force R using the JIS type shoe cone 20 and the tapered shoe cone 30 shown in FIG. (1) When a JIS type shoe cone 20 is used as the first shoe cone 150 and a JIS type shoe cone 20 is used as the second shoe cone 160, the N value is obtained as measurement value A to estimate the peripheral resistance force Rf, the N value is obtained as measurement value B to estimate the tip resistance force Rp, and the estimated peripheral resistance force Rf and tip resistance force Rp are used to estimate the indentation resistance force R. (2) When a tapered shoe cone 30 is used as the first shoe cone 150 and a JIS type shoe cone 20 is used as the second shoe cone 160, the T value is obtained as measurement value A to estimate the peripheral resistance force Rf, the N value is obtained as measurement value B to estimate the tip resistance force Rp, and the estimated peripheral resistance force Rf and tip resistance force Rp are used to estimate the indentation resistance force R. (3) When a tapered shoe cone 30 is used as the first shoe cone 150 and a tapered shoe cone 30 is used as the second shoe cone 160, the T value is obtained as measurement value A to estimate the peripheral resistance force Rf, the T value is obtained as measurement value B to estimate the tip resistance force Rp, and the estimated peripheral resistance force Rf and tip resistance force Rp are used to estimate the indentation resistance force R.

[0042] The above method (1) is essentially the same as the standard penetration test method (JIS A 1219:2013), so this application will mainly describe the above methods (2) and (3).

[0043] Figures 7 to 9 show examples of soil logs (depths of 1 to 75 m) created using the T and N values in the case of method (2) above. Note that Figure 7 shows the soil log from 1 to 30 m, Figure 8 shows the soil log from 31 to 50 m, and Figure 9 shows the soil log from 51 to 75 m.

[0044] As shown in FIGS. 7 to 9, the soil columnar diagrams show N values and T values obtained according to the number of hits of the hammer 103 for each depth and soil type.

[0045] FIG. 10 is a diagram showing a calculation formula for calculating the peripheral friction force fs and the ultimate tip support qd from the N value and the T value.

[0046] FIG. 10(a) shows a calculation formula for calculating the skin friction force fs(N) based on the N value obtained as measurement A using the JIS-type shoe cone 20 shown in FIG. 6(a). FIG. 10(b) shows a calculation formula for calculating the ultimate tip bearing capacity qd(N) based on the N value obtained as measurement B using the JIS-type shoe cone 20 shown in FIG. 6(a). FIG. 10(c) shows a calculation formula for calculating the skin friction force fs(T) based on the T value obtained as measurement A using the tapered shoe cone 30 shown in FIG. 6(b). FIG. 10(d) shows a calculation formula for calculating the ultimate tip bearing capacity qd(T) based on the T value obtained as measurement B using the tapered shoe cone 30 shown in FIG. 6(a). Note that FIG. 10 shows an example of a calculation formula for installing steel pipe piles in a port. Similarly, when steel pipe piles are used for roads, railways, or buildings, calculation formulas appropriate for each are used.

[0047] The estimation of the indentation resistance force R (S12 in FIG. 1) will be described below.

[0048] The skin resistance Rf(N) using the N value can be estimated using the following formula: Rf(N)=U·Σ(Li·fsi(N))···(4) where U is the perimeter of the pile (m), Li is the thickness of the i-th layer (m), and fsi (N) is the skin friction force of the i-th layer. For fsi (N), see Figure 10(a).

[0049] The tip resistance Rp (N) using the N value can be estimated using the following formula. Rp(N)=qd(N)·A·η···(5) where qd(N) is the ultimate bearing capacity, A is the pile tip area (m2), and η is the blockage rate. For qd(N), see Figure 10(b).

[0050] The skin resistance Rf(T) using the T value can be estimated using the following formula: Rf(T)=U·Σ(Li·fsi(T))···(6) where U is the perimeter of the pile (m), Li is the thickness of the i-th layer (m), and fsi(T) is the skin friction force of the i-th layer. For fsi(T), see Figure 10(c).

[0051] The tip resistance Rp(T) using the T value can be estimated using the following formula: Rp(T)=qd(T)·A·ηst···(7) where qd(T) is the ultimate end bearing capacity, A is the pile end area (m2), and ηst is the blockage rate relative to the pile diameter in the straight section. For qd(T), see Figure 10(d).

[0052] The indentation resistance force R obtained by the above method (1) can be estimated by the following formula: R = Rf(N) + Rp(N) (8) The above method (1) refers to a case where a JIS type shoe cone 20 is used as the first shoe cone 150 and a JIS type shoe cone 20 is used as the second shoe cone 160, an N value is obtained as measurement value A to estimate the skin resistance force Rf, an N value is obtained as measurement value B to estimate the tip resistance force Rp, and the estimated skin resistance force Rf and tip resistance force Rp are used to estimate the indentation resistance force R. The above method (1) essentially utilizes the same method as the standard penetration test method (JIS A 1219:2013).

[0053] The indentation resistance force R obtained by the above method (2) can be estimated by the following formula: R = Rf(T) + Rp(N) (9) The above method (2) refers to a case in which a tapered shoe cone 30 is used as the first shoe cone 150 and a JIS type shoe cone 20 is used as the second shoe cone 160, a T value is obtained as measurement value A to estimate the skin resistance Rf, an N value is obtained as measurement value B to estimate the tip resistance Rp, and the estimated skin resistance Rf and tip resistance Rp are used to estimate the indentation resistance R. In the above method (2), the measurement value A using the tapered shoe cone 30 is obtained as the T value to estimate the skin resistance Rf, and therefore this corresponds to an example of the skin resistance estimation method and the indentation resistance estimation method of the present application.

[0054] The indentation resistance force R obtained by the above method (3) can be estimated by the following formula: R = Rf(T) + Rp(T) (10) The above method (3) refers to a case in which a tapered shoe cone 30 is used as the first shoe cone 150 and a tapered shoe cone 30 is used as the second shoe cone 160, a T value is obtained as measurement value A to estimate the skin resistance Rf, a T value is obtained as measurement value B to estimate the tip resistance Rp, and the estimated skin resistance Rf and tip resistance Rp are used to estimate the indentation resistance R. In the above method (3), the measurement value A using the tapered shoe cone 30 is obtained as the T value to estimate the skin resistance Rf, and therefore this corresponds to an example of the skin resistance estimation method and the indentation resistance estimation method of the present application.

[0055] In the above, methods (2) and (3) have been described as methods for estimating the indentation resistance force R. First, the T value is acquired as the measurement value A, and then the peripheral resistance force Rf is estimated using the T value. However, the peripheral resistance force Rf may also be estimated from the ratio of the T value acquired as the measurement value A and the N value acquired as the measurement value B.

[0056] Furthermore, when obtaining measurement value A, a sampler is used in which a first shoe cone, which is a shoe cone with a tapered tip, is attached to the tip of a rod. However, when obtaining measurement value A, a sampler in which a third shoe cone, which is a shoe cone whose pile outer shape does not change from the tip to the head of the pile, is attached to the tip of a rod may be used instead of a sampler in which a first shoe cone is attached to the tip of a rod. Furthermore, when obtaining measurement value A, both a sampler in which a first shoe cone is attached to the tip of a rod and a sampler in which a third shoe cone is attached to the tip of a rod may be used.

[0057] The above describes a method for estimating the skin resistance Rf, tip resistance Rp, and compressive resistance R of a steel pipe pile. However, the estimation method according to the present invention can estimate the skin resistance Rf, tip resistance Rp, and compressive resistance R of not only steel pipe piles, but also precast piles including precast concrete piles including PHC piles, and cast-in-place piles. The estimation method according to the present invention can also estimate the skin resistance Rf, tip resistance Rp, and compressive resistance R of driven piles used in the hammering method.

[0058] The estimation of the action on the pile head (S13 in Fig. 1) will be explained below. "Action on pile head" refers to the load (Sd) acting on the pile head, and refers to the load acting in the vertical (axial) direction of the pile, ignoring horizontal loads caused by waves, wind, earthquakes, etc. The load acting in the vertical (axial) direction of the pile mainly includes the weight of the materials (concrete and rebar) that make up the structure that the pile supports, so it is determined by calculation from the design drawings of the structure, etc.

[0059] The design of the tapered pile (S14 in Figure 1) will be explained below. The longer the pile length (= p1 + p2), the greater the layer thickness Li where the pile contacts the surrounding ground, and therefore the greater the skin resistance force Rf. The larger the pile head diameter p4, the greater the perimeter of the pile, and therefore the greater the skin resistance force Rf. Taking into consideration the relationship between the pile and the ground described above, the parameters of the pile length (p1 + p2) and pile head diameter p4 are determined so as to satisfy the bearing capacity verification formula (11) shown below. After determining the parameters of the pile length and pile head diameter p4, the other parameters are determined sequentially. In formula (11), "m" is an adjustment coefficient, for example, 1.5. (Sd×m) / R≦1.0 (11)

[0060] Figure 11 shows a specific example of a tapered pile designed based on the estimated "push-in resistance force R" and the "load acting in the vertical (axial) direction of the pile" obtained from design drawings, etc.

[0061] Figure 11(a) shows the design of a straight pile for which the load of a specified building or other structure is expected, using the soil column shown in Figure 11(d) and the method (1) above to estimate the compressive resistance R using equation (8). Figure 11(d) shows an example of a soil column created by measuring the N-value and T-value for a certain soil type. As shown in Figure 11(a), the length of the straight pile is 70 m and the diameter is 1000 mm. Figure 11(a) shows a straight pile designed using a method essentially similar to the Standard Penetration Test Method (JIS A 1219:2013).

[0062] Figure 11(b) shows the design of a tapered pile for a given expected load, such as a building, using the soil column shown in Figure 11(d) and the method described in (1) above to estimate the compressive resistance R using Equation (8). As shown in Figure 11(b), the tapered pile has a straight section p1 = 60 m, a tapered section p2 = 3 m, a taper angle pθ = 2°, a pile tip diameter p3 = 790 mm, and a pile head diameter p4 = 1000 mm. Figure 11(b) shows the tapered pile designed using a method essentially similar to the Standard Penetration Test Method (JIS A 1219:2013).

[0063] Figure 11(c) shows the design of a tapered pile for a given expected load (Sd) from a given building, using the soil column shown in Figure 11(d) and the method described above (3), estimating the compressive resistance R using Equation (10). Based on the relationship in Equation (11), the parameters of the pile length of 55 m and the pile head diameter p4 of 1000 mm are determined. Next, based on experience, the tapered section p2 is preferably at least three times the pile head diameter p4, so the tapered section p2 is determined to be 3 m. Next, since the straight section p1 is the pile length minus the tapered section p2, the straight section p1 is determined to be 52 m. Next, based on existing laboratory tests, the taper angle pθ is determined to be 2°. Finally, the tip pile diameter p3 is determined to be 790 mm, based on the equation (p4 - 2 × tapered section p2 × tan(pθ)). In FIG. 11(c), a tapered pile is designed using the method for estimating skin resistance and the method for estimating compressive resistance of the present application.

[0064] As can be seen from Figures 11(a) to 11(c), by estimating the skin resistance Rf(T) using the T value, or by performing a rough estimation of the compressive resistance including estimating the skin resistance Rf(T) using the T value, it is possible to provide a skin resistance estimation method and a compressive resistance estimation method for designing better tapered piles.

[0065] It should be understood that those skilled in the art can make various changes, substitutions and alterations thereto without departing from the spirit and scope of the present invention. [Example]

[0066] In order to estimate the expansion effect of tapered piles, small-scale dynamic penetration tests simulating standard penetration tests were conducted using straight and tapered piles, and the change in sampler tip load depending on the expansion ratio and taper length of the straight and tapered piles was measured.

[0067] Figure 12(a) is a schematic diagram of the test equipment used in the small-scale dynamic penetration test, and Figure 12(b) is a diagram showing the model ground used in the small-scale dynamic penetration test.

[0068] The test device 200 has a model ground 201, a resin pipe 202, a guide rod 203, an anvil 204, a buffer material 205, and a weight 206, and the weight 206 is dropped onto the anvil 204 to cause a rod 207 to penetrate into the model ground 201. A sampler according to the comparative example and the example is attached to the tip of the rod 207, and a load cell (not shown) is arranged to detect the tip load applied to the rod 207. The model ground 201 has a diameter of 570 mm and is prepared in a stainless steel soil tank with a height of 890 mm by using a hopper to load silica sand No. 7 as a sample, with a relative density Dr of approximately 60% by the air drop method. The lower part 211 of the model ground 201 has a height L L The upper part 212 of the model ground 201 has a height L H The hole has a length of 300 mm, and a resin pipe 202 is placed therein, forming a recess 208 simulating a drilled hole.

[0069] The resin pipe 202 is made of polyvinyl chloride and is arranged around the guide rod 203 and rod 207 so as to surround the recess 208. The guide rod 203 has a rod-like shape extending vertically, to which the anvil 204 and buffer material 205 are fixed, and which supports the weight 206 so that it can move in the extension direction. The anvil 204 has a substantially conical shape and is fixed to the guide rod 203. The buffer material 205 has a thickness of 20 mm and is arranged on the upper surface of the anvil 204. The buffer material 205 prevents energy loss caused by the weight 206 bouncing back when it falls and hits the anvil 204. The weight 206 has a cylindrical shape and is dropped a distance L from the upper surface of the anvil 204. F The weight 206 has a mass of 5 kg and falls a distance L F is 110 mm, and the impact energy density of the test device 200 is one-tenth of the impact energy density of the standard penetration test.

[0070] FIG. 13 shows samplers according to Comparative Examples 1 to 3 and Examples 1 to 5 attached to the tip of rod 207, and Table 1 shows the dimensions of the samplers according to Comparative Examples 1 to 3 and Examples 1 to 5. FIG. 13(a) shows the sampler according to Comparative Example 1, FIG. 13(b) shows the sampler according to Comparative Example 2, and FIG. 13(c) shows the sampler according to Comparative Example 3. FIG. 13(d) shows the sampler according to Example 1, FIG. 13(e) shows the sampler according to Example 2, FIG. 13(f) shows the sampler according to Example 3, FIG. 13(g) shows the sampler according to Example 4, and FIG. 13(h) shows the sampler according to Example 5.

[0071] [Table 1]

[0072] Using the test device 200, the number of blows Nd until the samplers according to Comparative Examples 1 and 2 and Examples 1 and 2 penetrated into the model ground 201 to a position 300 mm from the upper surface of the lower part 211 of the model ground 201 was measured. Also, using the test device 200, the change in the tip load applied to the rod 207 was measured until the samplers according to Comparative Examples 1 and 2 and Examples 1 and 2 penetrated into the model ground 201 to a position 300 mm from the upper surface of the lower part 211 of the model ground 201. Furthermore, the tip load applied to the rod 207 when the samplers according to Comparative Examples 1 to 3 and Examples 1 to 5 penetrated into the model ground 201 to a position near 300 mm from the upper surface of the lower part 211 was measured.

[0073] Fig. 14 is a diagram showing the change in the number of blows Nd until the samplers according to Comparative Examples 1 and 2 and Examples 1 and 2 penetrate into the model ground 201 to a position 300 mm from the top surface of the lower part 211 of the model ground 201. In Fig. 14, the vertical axis represents depth, and the horizontal axis represents the number of blows. Furthermore, D101 represents the change in the sampler according to Example 1, D102 represents the change in the sampler according to Example 2, D103 represents the change in the sampler according to Comparative Example 1, and D104 represents the change in the sampler according to Comparative Example 2.

[0074] Number of blows until penetration reaches 300 mm N d The number of hits N was 22 for the sampler according to Comparative Example 1 and 39 for the sampler according to Comparative Example 2. The diameter expansion ratio of the sampler according to Comparative Example 1 was 1.13 and the diameter expansion ratio of the sampler according to Comparative Example 2 was 2.30. d It was found that the number of blows N until the hole penetrated to 300 mm was approximately proportional to the expansion ratio. d The number of hits N was 34 for the sampler according to Example 1 and 49 for the sampler according to Example 2. The diameter expansion ratio of the sampler according to Example 1 was 1.32 and the diameter expansion ratio of the sampler according to Example 2 was 2.30, so that the number of hits N was 34 for the sampler according to Example 1 and 49 for the sampler according to Example 2, as with the sampler according to the comparative example. d It was found that is approximately proportional to the expansion ratio.

[0075] Figure 15(a) is a diagram showing the change in tip load applied to the rod 207 while the samplers according to Comparative Examples 1 and 2 and Examples 1 and 2 are penetrated into the model ground 201 to a position 300 mm from the top surface of the lower part 211 of the model ground 201. In Figure 15(a), the horizontal axis represents depth, and the vertical axis represents tip load. Furthermore, L101 represents the change in the sampler according to Example 1, L102 represents the change in the sampler according to Example 2, L103 represents the change in the sampler according to Comparative Example 1, and L104 represents the change in the sampler according to Comparative Example 2.

[0076] In both the samplers according to the comparative example and the samplers according to the examples, it was confirmed that the tip load of the samplers according to comparative example 2 and example 2, which have a large expansion ratio, is larger than the tip load of the samplers according to comparative example 1 and example 1, which have a small expansion ratio, and that they are more likely to exhibit supporting force. In comparing the tip loads of the samplers according to comparative example 2 and example 2, which have the same expansion ratio, it was confirmed that the tip load of the sampler according to example 2 is larger than the tip load of the sampler according to comparative example 2.

[0077] Figure 15(b) shows the tip load applied to the rod 207 when the samplers according to Comparative Examples 1 to 3 and Examples 1 to 5 are inserted into the model ground 201 to a depth of approximately 300 mm from the top surface of the lower part 211. In Figure 15(b), the horizontal axis represents the expansion ratio, and the vertical axis represents the tip load. P101 represents the sampler according to Example 1, P102 represents the sampler according to Example 2, P103 represents the sampler according to Example 3, P104 represents the sampler according to Example 2, and P105 represents the sampler according to Example 5. P106 represents the sampler according to Comparative Example 1, P107 represents the displacement of the sampler according to Comparative Example 2, P104 represents the sampler according to Comparative Example 2, and P108 represents the sampler according to Comparative Example 3.

[0078] The tip loads of the samplers according to Comparative Examples 1 to 3 and Examples 1 to 5 depend on the taper length, but are highly dependent on the expansion ratio, increasing as the expansion ratio increases. It was confirmed that the rate of increase in the tip load of the sampler was large when the expansion ratio was less than 1.5 and small when the expansion ratio was 1.5 or more. [Example]

[0079] To estimate the spreading effect of the tapered piles, a penetration test was conducted on both straight and tapered piles, performing the process shown in Figure 3 to obtain measurements A and B. The penetration test then performed the processes shown in S20 to S28 after the processes shown in S29 to S37. The penetration test was conducted by penetrating a sampler 24 m into a reclaimed land facing Higashi-Harima Port in Hyogo Prefecture. The reclaimed land where the penetration test was conducted consisted of a clayey sand and gravel layer from the surface to a depth of approximately 13 m, while the layer deeper than 13 m consisted of clayey sand and gravel. During the penetration test, the displacement of the pile with each blow of the hammer was also measured using a Pile Driving Monitor (PDM) manufactured by Pile Dynamics Inc.

[0080] Measurement B was measured using the straight pile shown in Figure 16(a), and measurement B was measured using the tapered pile shown in Figure 16(b). The tapered pile shown in Figure 16(b) was designed so that the length of the tapered part was three times the maximum diameter.

[0081] In the penetration tests, in the test hole drilling shown in S21 and S32, the pile was drilled to a depth of 50 cm, in the pre-driving shown in S25 and S34, the pile was penetrated to a depth of 15 cm, and in the main driving shown in S26 and S35, the pile was penetrated to a depth of 30 cm. Measurement A and measurement B were defined as the number of blows required to penetrate the pile to a depth of 30 cm in the main driving.

[0082] Figure 17 and Table 2 show the changes in measurement values A and B as the depth of penetration of the sampler changes. In Figure 17, the vertical axis indicates depth, and the horizontal axis indicates the number of hits. In Table 2, the "0cm to 10cm" column indicates the number of hits when penetrating the first 10cm of a 30cm penetration. The "10cm to 20cm" column indicates the number of hits when penetrating the next 10cm of a 30cm penetration. The "20cm to 30cm" column indicates the number of hits when penetrating the last 10cm of a 30cm penetration. The "Total" column indicates the total number of hits when penetrating the 30cm penetration. Note that the number of hits of 60 or more is an estimate.

[0083] [Table 2]

[0084] In the clay layer from the surface to a depth of approximately 13m, measurement value A tends to be slightly larger than measurement value B, and in the clay-mixed gravel layer deeper than approximately 13m, the difference between measurement value A and measurement value B becomes more pronounced as the depth increases. It is thought that measurement value A is larger than measurement value B in the clay-mixed gravel layer because the tapered part of the tapered pile spreads the ground during the driving process, increasing the peripheral friction stress and the normal stress to the shoe surface. Also, with straight piles, the number of blows per 10cm is constant regardless of depth or decreases as the depth increases. On the other hand, with tapered piles, the number of blows per 10cm increases as the depth increases.

[0085] Figure 18(a) shows the change in depth per blow when a straight pile is installed in a layer approximately 13 m deep, and Figure 18(b) shows the change in depth per blow when a tapered pile is installed in a layer approximately 14 m deep. In Figures 18(a) and 18(b), the horizontal axis represents time and the vertical axis represents depth. The depths shown in Figures 18(a) and 18(b) were measured using a PDM.

[0086] For straight piles, the depth per blow remains roughly constant regardless of the number of blows. On the other hand, for tapered piles, the depth per blow decreases as the number of blows increases, because the tapered part of the tapered pile spreads the ground during the driving process and compacts the surrounding ground. [Explanation of symbols]

[0087] 10 Tapered piles 20 Straight Choux Cones 30 Tapered Shoe Cone 100 Penetration test device 100 110 rods 140 Sampler 150 First Choux Cone 160 2nd Choux Cone

Claims

1. A method for estimating a skin resistance for designing a pile having at least a tapered tip, comprising: Using at least one of a sampler having a first shoe cone attached to the tip of a rod and a sampler having a third shoe cone attached to the tip of a rod, the number of hits required to drive the sampler a predetermined length is obtained as a measurement value A; Using the measured value A, a step of estimating a skin resistance force is included; the first shoe cone is a shoe cone having a tapered tip, The third shoe cone is a shoe cone whose pile outer shape does not change from the pile tip to the pile head. A method for estimating skin resistance.

2. 2. The method for estimating peripheral resistance force according to claim 1, wherein the first shoe cone includes a cylindrical straight portion on the side connected to the rod, and a tapered portion connected to the straight portion and having a side surface whose diameter decreases at a predetermined taper angle in the direction of the central axis of the first shoe cone.

3. A method for estimating a compressive resistance force for designing a pile having at least a tapered tip portion, comprising: Using at least one of a sampler having a first shoe cone attached to the tip of a rod and a sampler having a third shoe cone attached to the tip of a rod, the number of hits required to drive the sampler a predetermined length is obtained as a measurement value A; Using a sampler with a second shoe cone attached to the tip of a rod, the number of hits required to drive the sampler a predetermined length is obtained as a measurement value B; Using the measured value A, the peripheral resistance force is estimated, Using the measurement B, estimate the tip resistance force; estimating a push-in resistance force based on the estimated tip resistance force and the estimated peripheral resistance force, the first shoe cone is a shoe cone having a tapered tip, The third shoe cone is a shoe cone whose pile outer shape does not change from the pile tip to the pile head. A method for estimating indentation resistance force.

4. 4. The method for estimating indentation resistance force according to claim 3, wherein the first shoe cone includes a cylindrical straight portion on the side connected to the rod, and a tapered portion connected to the straight portion and having a side surface whose diameter decreases at a predetermined taper angle in the direction of the central axis of the first shoe cone.

5. The method for estimating indentation resistance force according to claim 3 or 4, wherein the second shoe cone has a different shape from the first shoe cone and the third shoe cone.

6. Estimate the skin resistance of piles with at least the tip tapered, Estimate the compressive resistance of the pile; A pile design method for designing the pile based on the skin resistance and the push-in resistance, wherein the process of estimating the skin resistance comprises: Using at least one of a sampler having a first shoe cone attached to the tip of a rod and a sampler having a third shoe cone attached to the tip of a rod, the number of hits required to drive the sampler a predetermined length is obtained as a measurement value A; Using the measured value A, a step of estimating a skin resistance force is included; The first shoe cone is a shoe cone having a tapered tip. A pile design method characterized by:

7. Estimate the skin resistance of piles with at least the tip tapered, Estimate the compressive resistance of the pile; A pile design method for designing the pile based on the peripheral resistance and the compressive resistance, wherein the process of estimating the compressive resistance includes: Using at least one of a sampler having a first shoe cone attached to the tip of a rod and a sampler having a third shoe cone attached to the tip of a rod, the number of hits required to drive the sampler a predetermined length is obtained as a measurement value A; Using a sampler with a second shoe cone attached to the tip of a rod, the number of hits required to drive the sampler a predetermined length is obtained as a measurement value B; Using the measured value A, the peripheral resistance force is estimated, Using the measurement B, estimate the tip resistance force; estimating a push-in resistance force based on the estimated tip resistance force and the estimated peripheral resistance force, the first shoe cone is a shoe cone having a tapered tip, The third shoe cone is a shoe cone whose pile outer shape does not change from the pile tip to the pile head. A pile design method characterized by:

8. Estimate the skin resistance of piles with at least the tip tapered, Estimate the compressive resistance of the pile; A pile designed based on the periphery resistance and the push-in resistance, wherein the process of estimating the periphery resistance is Using at least one of a sampler having a first shoe cone attached to the tip of a rod and a sampler having a third shoe cone attached to the tip of a rod, the number of hits required to drive the sampler a predetermined length is obtained as a measurement value A; Using the measured value A, a step of estimating a skin resistance force is included; the first shoe cone is a shoe cone having a tapered tip, The third shoe cone is a shoe cone whose pile outer shape does not change from the pile tip to the pile head. A pile characterized by:

9. Estimate the skin resistance of piles with at least the tip tapered, Estimate the compressive resistance of the pile; A pile designed based on the peripheral resistance and the compressive resistance, wherein the process of estimating the compressive resistance is Using at least one of a sampler having a first shoe cone attached to the tip of a rod and a sampler having a third shoe cone attached to the tip of a rod, the number of hits required to drive the sampler a predetermined length is obtained as a measurement value A; Using a sampler with a second shoe cone attached to the tip of a rod, the number of hits required to drive the sampler a predetermined length is obtained as a measurement value B; Using the measured value A, the peripheral resistance force is estimated, Using the measurement B, estimate the tip resistance force; estimating a push-in resistance force based on the estimated tip resistance force and the estimated peripheral resistance force, the first shoe cone is a shoe cone having a tapered tip, The third shoe cone is a shoe cone whose pile outer shape does not change from the pile tip to the pile head. A pile characterized by:

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