Design method for widening piles

Abstract

To provide a design method of a widening pile capable of rationally determining a pile shape.SOLUTION: A design method of a widening pile has an initial value setting step of setting initial values of a shaft diameter and a widening diameter, an extraction resistance force calculation step of calculating an extraction resistance force (Q) of a widening part required from an external force condition using a reference stress (σstd) calculated from expression (1), a first shape determination step of determining whether the initial values satisfy any one of expressions (2) and (3), a shape changing step of changing at least one of a widening angle, an excavation depth and a widening diameter, when it is determined in the first shape determination step that the initial values do not satisfy the expressions, and a second shape determination step of determining whether the initial values satisfy any one of the expressions (2) and (3) after the shape changing step. When it is determined in the second shape determination step that the initial values do not satisfy the expressions, the method returns to the shape changing step.SELECTED DRAWING: Figure 11

Description

Technical Field

[0001] The present invention relates to a design method for an enlarged pile.

Background Art

[0002] <00​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Therefore, the present invention has been made in view of the above-mentioned problems, and aims to provide a design method for widened piles that can rationally determine the pile shape. [Means for solving the problem]

[0006] To achieve the above objective, the present invention provides a design method for widened piles having a shaft portion and a widened portion that is continuous with the shaft portion and whose diameter gradually increases as it moves away from the shaft portion, comprising: an initial value setting step of setting initial values ​​for the diameter of the shaft portion and the diameter of the widened portion; and a standard stress (σ) calculated from the following formula (1) for the pull-out resistance force (Q) of the widened portion required from the external force conditions. std The process includes: a pull-out resistance calculation step calculated using ), a first shape determination step determining whether the initial value is a shape that satisfies either of the following equations (2) and (3), a shape modification step changing at least one of the angle of the widening section, the excavation depth, and the diameter of the widening section if it is determined in the first shape determination step that neither of the following equations (2) and (3) are satisfied, and a second shape determination step determining whether the shape satisfies either of the following equations (2) and (3) after the shape modification step, and if it is determined in the second shape determination step that neither of the following equations (2) and (3) are satisfied, the process returns to the shape modification step.

[0007]

number

[0008] This invention can be applied to widened piles with a widening diameter exceeding 3m, which was not possible with conventional methods, and allows for a rational determination of the pile shape. Furthermore, it enables the determination of the shape of the widened section while considering the dimensional effects of the widened section, which were not considered in conventional methods.

[0009] Furthermore, in the design method for widened piles according to the present invention, the numerical values ​​may be changed in the shape modification step in the order of priority of the angle of the widened portion, the excavation depth, and the diameter of the widened portion.

[0010] The reason for starting with changing the widening angle is that it is a parameter that does not change the vertical downward support performance. In other words, changing the widening angle does not change the vertical downward support force. Changing the vertical downward support force changes the load distribution of the entire building, and it becomes necessary to reconsider the balance of forces of the entire structure (design change), but changing the widening angle does not require reconsidering the balance of forces of the entire structure. The reason for changing the excavation depth after changing the widening angle is that it does not require changing the excavation machinery. However, if the diameter of the widened section is increased, it may be necessary to change the excavation machinery. For example, if the excavation depth cannot be changed (increased) due to the strong supporting layer making excavation difficult, the diameter of the widened section is changed (expanded) until the required pull-out resistance is secured. In this way, the shape of the widened pile can be rationally determined by changing the values ​​in the following order of priority during the shape modification process: the angle of the widened section, the excavation depth, and the diameter of the widened section. [Effects of the Invention]

[0011] According to the present invention, the pile shape can be determined rationally. [Brief explanation of the drawing]

[0012] [Figure 1] This is a vertical cross-sectional view of the widening pile. [Figure 2] This is a plan view of the widening piles. [Figure 3] This figure shows the relationship between the widening ratio and the shape of the widened section in an experiment where the widening angle is varied. [Figure 4] This table shows the dimensions of the model of the widened pile in an experiment where the widening diameter is constant and the widening angle is varied. [Figure 5] This graph shows the relationship between the pull-out resistance force of the widened section and the pull-out displacement of the widened section in an experiment where the widening diameter is constant and the widening angle is varied. [Figure 6] This graph shows the relationship between the increment in the widening angle and the increment in the extreme pull-out resistance of the widened section in an experiment where the widening diameter is constant and the widening angle is varied. [Figure 7]This figure shows the change in the widening ratio. [Figure 8] This table shows the dimensions of the model of the widening pile used in an experiment where the height of the widening section is constant and the widening ratio is varied. [Figure 9] This graph shows the relationship between the pull-out resistance of the widened section and the amount of pull-out displacement of the widened section in an experiment where the height of the widened section is constant and the widening ratio is varied. [Figure 10] This graph shows the relationship between the widening ratio and the pull-out resistance of the dimensionless widened section. [Figure 11] This is a flowchart of the design method for widening piles. [Modes for carrying out the invention]

[0013] The design method for widening piles according to embodiments of the present invention will be described below with reference to Figures 1-11. The design method for widened piles according to this embodiment is used in the design of widened piles 1 having a shaft portion 2 and a widened portion 3 having a larger diameter than the shaft portion 2, as shown in Figures 1 and 2. The shaft portion 2 is cylindrical in shape and extends vertically. The widening portion 3 is frustoconical in shape with its axis extending vertically. The widening portion 3 is continuous below the shaft portion 2 and is integrally provided with the shaft portion 2. The diameter of the upper end of the widening portion 3 is equal to the diameter of the shaft portion 2. The diameter of the widening portion 3 gradually increases from the upper end to the lower end. In the following, the diameter of the shaft portion 2 will be referred to as the shaft diameter, and the diameter of the lower end of the widening portion 3 will be referred to as the widening diameter. The inclination angle of the outer surface of the widening portion 3 will be referred to as the widening angle. As described above, in this embodiment as well, the enlarged base pile and the enlarged diameter pile are collectively referred to as the enlarged pile, and the portion of the enlarged pile with a larger diameter is referred to as the enlarged portion 3.

[0014] The symbols and specifications used in the design method for widening piles are shown below. Figures 1 and 2 show the parts corresponding to the symbols. Q: Pull-out resistance of the widened section D: Pull-out displacement of the widened section b s : Shaft diameter b b : Widening diameter b': Widening length (=bb -b s ) e ratio : Expansion ratio (= b b / b s ) A b : Projected area of the expansion part α: Expansion angle σ b : Vertical stress of the expansion part σ e : Overburden pressure at the lower end depth of the expansion part σ int : Overburden pressure at the middle depth of the expansion part σ sh : Overburden pressure at the upper end depth of the expansion part

[0015] Expansion diameter (b b ) exceeds 3 m, a reduced-scale model experiment using a centrifugal loading device was carried out to measure the pullout resistance (Q) of the expansion part, and a pullout model experiment of the expansion pile up to the maximum diameter of 4 m (3.96 m) was carried out based on the similarity law. In the experiment, the expansion diameter (b b ) was kept constant and the expansion angle (α) was changed. Fig. 3 shows the relative relationship of the pile shapes used in the experimental series carried out with the expansion diameter (b b ) kept constant and the expansion angle (α) changed. The expansion pile 1 with an expansion angle (α) of 90° has a bottom plate 4 provided. Fig. 4 shows the dimensions of the model piles used in the experimental series carried out with the expansion diameter (b b ) kept constant and the expansion angle (α) changed. <了 Fig. 5 shows the pullout test results using the expansion pile shown in Fig. 3, and shows the relationship between the pullout displacement (D) - pullout resistance (Q) of the expansion part with the pullout resistance (Q) and the pullout displacement (D) of the expansion part dimensionless. The dimensionless is based on the following formula.

[0016]

Equation

[0017] The pullout resistance (Q) of the expansion part is the net pullout resistance acting only on the expansion part 3 with the self-weight and the friction of the shaft part 2 removed.

[0018] The standard stress (standard stress σ) used to non-dimensionalize the pull-out resistance force (Q) of the widened section. std ) is the surcharge pressure (σe) at the lower end depth of the widened section 3, and the surcharge pressure (σe) at the central and upper end depths of the widened section 3. int ,σ sh You may choose any value for ) The reference stress (σ) used for dimensionlessization. std Since ) is the superimposed pressure at the depth of interest, there is a relationship between it and the reference depth given by equation (1) below. In equation (1), H is the reference depth (m) and γ' is the effective unit weight.

[0019]

number

[0020] In Figure 6, the maximum values ​​of each curve in Figure 5 are plotted with the widening angle (α) on the horizontal axis. The symbols (◆) in Figure 6 are extracted values ​​of (↓MAX: ultimate pull-out resistance) shown in Figure 5. The slope obtained by linear interpolation for the symbols (◆) in Figure 6 is β. b This is the correspondence. The pull-out resistance force (Q) of the widened section has a linear relationship with the widening angle (α), and it can be seen that the maximum value of the pull-out resistance force (Q) of the widened section increases as the widening angle (α) increases.

[0021] Figure 7 shows that the height of the widened section 3 is kept constant, and the widening ratio (e ratio Figure 8 shows the relative relationships of the pile shapes used in the experimental series in which the ) was changed. The height of the widened section 3 is kept constant, and the widening ratio (e ratio The dimensions of the model piles used in the experimental series, which was conducted with modifications to the specifications, are shown. Figure 9 shows the pull-out resistance relationship between the pull-out resistance force (Q) of the widened section and the pull-out displacement (D) of the widened section, obtained by non-dimensionalizing the pull-out resistance force in the pull-out experiment using the widened pile 1 shown in Figure 7. In Figure 10, the maximum value of each curve in Figure 9 is plotted on the horizontal axis as the widening ratio (e ratio The diagram shows the result of taking the shape (indicated by the symbol (◆) in the diagram). The pull-out resistance force (Q) of the widened section is given by the widening ratio (eratio It can be seen that it decreases as ) increases. The symbols (△, ×, □, ◇, ○) shown in Figure 10 have a widening ratio (e ratio Since both the θ and the widening angle (α) change, the amplification factor (β) due to the widening angle (α) shown in Figure 6 is obtained. b This is the value after angle correction using ). The curve shown in Figure 10 (func.10deg-90deg.) represents different widening ratios (e ratio This curve connects the pull-out resistance force (Q) of widened sections having the same widening angle (α) at ​​the same widening angle (e ratio The relationship between the pull-out resistance force (Q) of the widened section is expressed by the following equations (2) and (3). In equations (2) and (3), C and n are constants for each widening angle (α) determined by experiment.

[0022]

number

[0023] From equation (3), the pull-out resistance force (Q) of the widened section is given by the standard stress (σ std ), or dimension term (e ratio n ·A b It can be seen that it is proportional to ). The standard stress (σ) in equation (3) std ) is proportional to the effective unit weight or depth according to equation (1), and increasing each of them increases the reference stress (σ std This can increase the pull-out resistance (Q) of the widened section. In other words, the pull-out resistance (Q) of the widened section can be increased by increasing the unit volume weight of the ground on which the widened section 3 is installed, or by installing the widened section 3 deeper.

[0024] The dimension term (e) in equation (3) ratio n ·A b ) widening diameter (b b Rearranging by , we obtain equation (4) below. In equation (4), 2+n is greater than 1 from the experiment.

[0025]

number

[0026] From equations (3) and (4), the shaft diameter (b s If ) is constant, then the widening diameter (b b Increasing the ) increases the dimension term. That is, widening diameter (b b By increasing the ), the pull-out resistance (Q) of the widened section can be increased.

[0027] Based on the above, in the design method for widened piles, the shape of the widened section 3 is determined from the pull-out resistance force (Q) of the widened section as follows. Figure 11 shows a flowchart of the design method for widened piles (chart for determining the shape of the widened section having a predetermined pull-out resistance force).

[0028] Shaft diameter (b) s ) and widening diameter (b b An initial value setting process (S-1) is performed to set the initial value of ). In the initial value setting process (S-1), the shaft diameter (b) is determined by the design process. s ) and widening diameter (b b The initial value of ) is calculated from the vertical bearing force in the vertically downward direction.

[0029] Next, the pull-out resistance calculation process (S-2) is performed to calculate the pull-out resistance force (Q) of the widened section required by external force conditions such as seismic loads and wind loads. In the pull-out resistance calculation process, the pull-out resistance (Q) of the widened section is calculated from the above formula (1).

[0030] Next, a first shape determination step (S-3) is performed to determine whether the initial value set in the initial value setting step (S-1) is a shape that satisfies either of the above equations (2) and (3).

[0031] If it is determined in the first shape determination step that either of the above equations (2) and (3) is satisfied, the shape determination step (S-4) for determining the shape of the widening pile is performed.

[0032] If it is determined in the first shape determination step (S-3) that neither of the above equations (2) and (3) is satisfied, the widening angle (α), excavation depth (H), and widening diameter (b) are determined. b A shape modification step (S-5) is performed, which modifies at least one of the following: In the shape modification process (S-5), the pile shape is determined based on Figure 10 (either equation (2) or (3) above), with one of the above equations (2) or (3) as a variable and the other as an initial value. The required pull-out resistance (Q) req. ) and the calculated pull-out resistance (Q est. The difference between (dQ=Q) req. -Q est. From these, we obtain the angle increment (dα), depth increment (dH), and widening diameter increment (db). b Calculate ).

[0033] If the widening angle (α) can be changed, the required pull-out resistance force (Q) req. Increase the widening angle (α) until the required pull-out resistance (Q) is satisfied (widening angle α → α + dα). req. If we consider increasing the widening angle (α) until ), the required angle increment (dα) is as follows. dα = dQ / β b If the drilling depth (H) can be changed, the required pull-out resistance (Q) req. Increase the drilling depth (H) until the required pull-out resistance (Q) is satisfied (drilling depth H → H + dH). req. If we consider increasing the drilling depth (H) until ), the required depth increment (dH) is as follows: dH=dQ / γ' Widening diameter (b b If possible, change the required pull-out resistance (Q req. ) until the widening diameter (b) is satisfied b ) increases (widening diameter b b →b b +db b ). Required pull-out resistance (Q req. The widening diameter (b) until it becomes ) b When considering increasing the width, the required increase in the widening diameter (db)b The results are as follows: db b =dQ / (∂Q / ∂b b )) Note that the increase in the widening diameter (db) b While it would be complicated to express this in a specific formula, the formalization is as shown above.

[0034] As shown in Figure 11, in the shape modification process (S-5), the widening angle (α), excavation depth (H), and widening diameter (b) are changed. b The values ​​will be changed in the following order of priority. The reason will be explained later.

[0035] After the shape modification step (S-5), a second shape determination step (S-6) is performed to determine whether the shape satisfies either of the above equations (2) and (3), similar to the first shape determination step. If it is determined in the second shape determination step (S-6) that neither of the above equations (2) and (3) are satisfied, the process returns to the shape modification step, and at least one of the widening angle (α), excavation depth (H), and diameter of the widened section is changed. If it is determined in the second shape determination step (S-6) that either of the above equations (2) and (3) is satisfied, the shape determination step (S-4) for determining the shape of the widening pile is performed.

[0036] As mentioned above, in the shape modification process (S-5), the widening angle (α), excavation depth (H), and widening diameter (b) are changed. b The values ​​are changed in the following order of priority. The priority order of the variables to be changed in the shape modification process (S-5) is as follows:

[0037] The reason for starting with changing the widening angle (α) is that it is a parameter that does not change the vertical downward support performance. In other words, changing the widening angle (α) does not change the vertical downward support force. Changing the vertical downward support force changes the load distribution of the entire building, requiring a re-examination (design change) of the balance of forces in the entire structure. However, changing the widening angle (α) does not require a re-examination of the balance of forces in the entire structure. The reason for changing the drilling depth (H) after changing the widening angle (α) is that it does not involve changing the drilling machine. Note that the widening diameter (b b If the project is expanded, it may be necessary to change the excavating machinery. For example, if the excavation depth (H) cannot be changed (to make it deeper) due to the strong supporting layer making excavation difficult, the widening diameter (b) may be increased until the predetermined pull-out resistance force (Q) of the widened section is secured. b ) is changed (expanded). In this way, in the shape modification process (S-5), the widening angle (α), excavation depth (H), and widening diameter (b) are changed. b By changing the values ​​in the order of priority listed above, the shape of the widening piles can be rationally determined.

[0038] Next, the operation and effects of the design method for widened piles according to this embodiment will be explained. In the design method for widened piles according to this embodiment, the widened diameter (b) which could not be achieved conventionally is possible. b This method can be applied to widened piles exceeding 3m in length, allowing for a rational determination of the pile shape. Furthermore, it enables the determination of the shape of the widened section while considering the dimensional effects of the widened section, which were not considered in conventional methods.

[0039] Although embodiments of the design method for widening piles according to the present invention have been described above, the present invention is not limited to the above embodiments and can be modified as appropriate without departing from the spirit of the invention. For example, in the above embodiment, the shape modification step (S-5) involves the widening angle (α), excavation depth (H), and widening diameter (b b The values ​​are changed in the order listed above, but you may change them in any other order. [Explanation of Symbols]

[0040] 1. Widening piles 2. Shaft section 3 Widening section b b Widening diameter (diameter of the widened section) b s Shaft diameter (diameter of the shaft) D. Displacement of the widened section H drilling depth Q: Pull-out resistance of the widened section α Widening angle (angle of the widened section) σ std Reference stress S-1 Initial value setting process S-2 Resistance force calculation process S-3 First shape determination process S-4 Shape determination process S-5 Shape Change Process S-6 Second shape determination process

Claims

1. A design method for a widened pile having a shaft portion and a widened portion that is continuous with the shaft portion and whose diameter gradually increases as it moves away from the shaft portion, An initial value setting step of setting initial values ​​for the diameter of the shaft portion and the diameter of the widened portion, The pull-out resistance force (Q) of the widened section required from the external force conditions is calculated from the standard stress (σ) of the following formula (1). ｓｔｄ The process of calculating the pull-out resistance force using ) and A first shape determination step is to determine whether the initial value is a shape that satisfies either of the following equations (2) and (3), If it is determined in the first shape determination step that neither of the following equations (2) and (3) are satisfied, a shape modification step is performed to change at least one of the angle of the widened portion, the excavation depth, and the diameter of the widened portion. The process includes a second shape determination step, which determines whether the shape satisfies either of the following formulas (2) and (3) after the shape modification step, A design method for widening piles, which returns to the shape modification step if it is determined in the second shape determination step that neither of the following equations (2) and (3) are satisfied. [Math 1]

2. The design method for widened piles according to claim 1, wherein in the shape modification step, the numerical values ​​are changed in the order of priority of the angle of the widened portion, the excavation depth, and the diameter of the widened portion.

Images