Analysis of the Bearing Characteristics of Single Piles under Vertical and Torsional Combined Loads

Shun-Wei Wang,Jie Jiang,Juan Tang,Chen-Zhi Fu,Xiao-Duo Ou,Valeria Vignali

doi:10.1155/2021/8896673

Abstract

To investigate the bearing characteristics of single piles under the combined action of vertical loads (V) and torque (T) on a pile head, the displacement governing equations of the pile shaft were proposed in consideration of the load transfer method, and the nonlinear solution of a single-loaded pile (vertical load or torque) was calculated by the finite difference method. According to the above mentioned investigation, a new numerical analysis model was proposed to modify the vertical and circumferential ultimate friction resistance of the pile side. Subsequently, the nonlinear solutions of single piles under the combined loads of V-T loading with different loading paths were obtained by MATLAB programming, and the bearing capacity envelopes were plotted. Based on the comparison with the existing research results, the correctness of the theoretical calculation method proposed in this article was verified. The results show that compared with a single loaded pile (V or T), with the action of the V-T combined loads, the bearing capacity of a single pile will decrease, and the single piles under the V⟶T loading path will have a higher bearing capacity than those under the T⟶V loading path. When the aspect ratio is comparatively small, the influence of the loading path is negligible; however, when the aspect ratio is comparatively large, it is necessary to avoid the preliminary application of the torque to a single pile to prevent the decrease in the ultimate bearing capacity on account of the formation of the T⟶V loading mode. The deformation of the pile body mainly occurs in the range from 0 to 0.6L, so effective deformation reduction can be achieved by reinforcing the shallow foundation. It is inadvisable for a single friction pile to be used to improve the bearing capacity by increasing the concrete grade.

Highlights

To ensure the safety of buildings, pile foundations are often used in actual projects
Zhang et al [3] utilized a hyperbolic curve model to explain the lateral friction of single piles and a polyline model to simulate the hardening of the pile tip
Considering different loading paths, the pile bearing characteristics of the V-T composite loaded pile were explored through theoretical analysis. e main conclusions are summarized as follows: (1) e numerical solution of a single loaded pile was obtained by the finite difference method, and considering the influence of different loading paths, a new numerical analysis model was proposed to achieve the numerical solution of single piles under V-T combined loading

Summary

Introduction

To ensure the safety of buildings (structures), pile foundations are often used in actual projects. For single piles under the T⟶V loading path, the hoop friction resistance under the action of torque can be calculated first, and the vertical ultimate friction resistance can be determined by the following formula:. Where Nc and Nq are the dimensionless bearing capacity constants related to the internal friction angle, which can be determined by referring to the table, c is the cohesion of the soil, and q is the average vertical pressure on the side of the plane at pile tip, which can be obtained as follows: q. E drawing method of the single pile bearing capacity envelope under different loading paths is as follows: taking the V⟶T loading path as an example, the T-θt curves corresponding to different vertical loads Vi is obtained according to the method, the torque Tui corresponding to the reverse bending point of the curve is the limit torque under the V⟶T loading path. A similar method can be used to obtain the single pile bearing capacity envelope under the T⟶V loading path

Method Validation

Parameter Analysis

Findings

Conclusion