JP-7856511-B2 - Design method for widening piles

JP7856511B2JP 7856511 B2JP7856511 B2JP 7856511B2JP-7856511-B2

Inventors

桐山貴俊
周友昊
浅香美治

Assignees

清水建設株式会社

Dates

Publication Date: 20260511
Application Date: 20220704

Claims (2)

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, A pull-out resistance calculation process is performed to calculate the pull-out resistance force (Q) of the widened portion required from the external force conditions using the reference stress (σ std ) calculated from the following formula (1), 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.
The design method for widened piles according to claim 1, wherein in the shape modification step, the values are changed in the following order of priority: the angle of the widened portion, the excavation depth, and the diameter of the widened portion.

Description

This invention relates to a design method for widening piles. As foundations for buildings, enlarged-base piles, where the base of the pile is larger in diameter than the head, and enlarged-diameter piles, which have a larger diameter section in the middle of the pile in the height direction, are known (see, for example, Patent Document 1). Hereinafter, enlarged-base piles and enlarged-diameter piles will be collectively referred to as enlarged-width piles, and the larger diameter section of an enlarged-width pile will be referred to as the enlarged-width section. Japanese Patent Publication No. 2019-183494 This is a vertical cross-sectional view of the widening pile.This is a plan view of the widening piles.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.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.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.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.This figure shows the change in the widening ratio.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.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.This graph shows the relationship between the widening ratio and the pull-out resistance of the dimensionless widened section.This is a flowchart of the design method for widening piles. 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 provided integrally 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. 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 force of the widened section D: Pull-out displacement of the widened section b s : Shaft diameter b b : Widened diameter b': Widened length (= b b - b s ) e ratio : widening ratio (=b b /b s ) A b : Projection area of the widened section α: Widening angle σ b : Vertical stress of the widened section σ e : Overload pressure at the lower end depth of the widened section σ int : Overload pressure at the intermediate depth of the widened section σ sh : Overload pressure at the upper end depth of the widened section To measure the pull-out resistance force (Q) of the widened section when the widened diameter ( b ) exceeds 3 m, a scaled-down model experiment was conducted using a centrifugal loading device, and based on the similarity law, pull-out model experiments were performed for widened piles up to a maximum diameter of 4 m (3.96 m). In the experiment, the widening diameter (b b ) was kept constant, while the widening angle (α) was varied. Figure 3 shows the relative relationships of the pile shapes used in the experimental series, in which the widening diameter (b b ) was kept constant and the widening angle (α) was changed. Widening pile 1, with a widening angle (α) of 90°, is provided with a base plate 4. Figur