Key Takeaways & Executive Findings
- •• A novel analytic method for plum blossom pile skin friction is developed, incorporating cross-sectional geometry and vertical shearing effects. • The method accurately predicts skin friction, negative skin friction, axial force, and dragload, validated against FEM and literature. • Increasing the shear action coefficient reduces axial force along the pile depth under vertical load. • The study provides a design tool for plum blossom piles, enhancing bearing capacity through perimeter enlargement.
Abstract
Plum blossom pile is a new type of special-shaped pile, which is proposed based on the principle of maximum perimeter with the same cross-sectional area. To advance this technique, primarily for the design of plum blossom piles, it is important to investigate the skin friction behavior of plum blossom pile foundations precluding any straightforward constitutive model. In this work, an analytic method dependent on the cross-sectional geometry and the vertical shearing effects is proposed by means of equilibrium analysis to calculate the effective vertical stress in the surrounding soil, the skin friction/negative skin friction, and the axial force/dragload of a plum blossom pile. Additionally, the curves of skin friction of piles are investigated with the same conditions. The results show that the curves of skin friction of piles deduced according to the developed analytic method agree well with the FEM results and related literature solution, which validates the solution. The axial force of the pile decreases with the increase of the shear action coefficient in the buried depth direction under the vertical concentrated load when considering the vertical shearing effects on the pile-soil interfaces.
1. Introduction
Plum blossom piles are designed to enhance the bearing capacity by enlarging the pile perimeter and altering the skin friction of the plum blossom piles. However, the skin friction of plum blossom piles is an important bearing part, and the analytic method of skin friction for plum blossom pile foundations is an important research focus. In practical engineering, it is generally considered that there are two types of pile skin friction, i.e., skin friction and negative skin friction, which is one of the most important problems in pile foundation design.
Scholars have carried out detail work and made fruitful progress in the load transfer behavior of piles [1−7]. These studies are very helpful in understanding the skin friction of the pile. However, previous literature paid little attention to the skin friction of special-shaped pile. Existing related research generally believes that there are two types of special-shaped piles. One is special cross-section shape pile, the other is varying diameters of pile. Especially in recent years, special-shaped piles, (large diameter cast-in situ concrete pipe pile (PCC pile) pile, X-section pile, H-pile, etc.) are widely used and studied [8−10].
Previous studies showed that special cross-section can improve side friction with the same concrete usage compared with traditional circular pile [11, 12]. ROLLINS et al [13] found that H-piles have greater pile-soil contact area, which can provide larger vertical skin friction. In other words, increasing the perimeter of the pile section is one of the effective methods to increase the bearing capacity of a pile. LV et al [14] conducted a series of static load tests in the field to compare the performance of a vertically loaded single X-section cast-in-place pile (XCC pile) pile and a circular pile with the same cross-sectional area and length. The results show that the XCC pile could provide 20% greater vertical bearing capacity than the conventional circular pile. Previous studies showed that enlarging the pile perimeter can alter the load transfer mechanism, and enhance the bearing capacity. On this basis, DENG et al [15, 16] proposed a novel kind of plum blossom pile with a cross section similar to a plum blossom, as shown in Figure 1.
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LI Long, JIANG Quan, DENG You-sheng (2025). Analytic method of skin friction for plum blossom pile foundations considering pile-soil interaction under vertical load. Journal of Central South University. https://doi.org/10.1007/s11771-025-6082-4
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Frequently Asked Questions
What is a plum blossom pile?
A plum blossom pile is a novel special-shaped pile with a cross-section resembling a plum blossom, designed to increase the pile perimeter and enhance bearing capacity compared to traditional circular piles of the same cross-sectional area.
How does the analytic method account for pile-soil interaction?
The method incorporates vertical shearing effects and cross-sectional geometry through equilibrium analysis, allowing calculation of effective vertical stress, skin friction, negative skin friction, axial force, and dragload.
What are the key findings of the study?
The proposed analytic method yields skin friction curves that agree well with FEM results and literature, and shows that axial force decreases with increasing shear action coefficient under vertical load.
Why is skin friction important for plum blossom piles?
Skin friction is a major component of pile bearing capacity. Understanding and accurately predicting skin friction is crucial for the design and performance evaluation of plum blossom pile foundations.
How does the plum blossom pile compare to traditional piles?
By enlarging the perimeter, plum blossom piles can provide greater skin friction and bearing capacity compared to circular piles with the same cross-sectional area, as demonstrated in previous studies.
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