Numerical study of a new belled wedge pile type under different loading modes

Abstract

A new pile type with tapered pile body and an enlarged pile tip, referred herein as belled wedge pile, has been developed to improve both side resistance and tip resistance of pile when compared to the conventional tapered or belled cross-section piles. The new pile shape, due to wedge shape, can also reduce the development of negative skin friction when the surrounding soils are deforming under the applied surcharge loads. The construction method, quality assurance and quality control of the belled wedge piles are described. A numerical modelling technique using FLAC^3D is used to perform numerical simulations to gain insight on the load carrying capacity and the load transfer behaviour of the belled wedge piles, in comparison to other pile shapes including the conventional belled piles, the tapered piles and uniform cross-section circular piles. The comparison study of the performance of these four pile shapes under compression loads, uplift loads and surcharge loads indicates that the belled wedge pile would possess the best load carrying capability and would be subjected to less downdrag among the four pile shapes evaluated. A parametric study using the established numerical modelling technique reveals the effects of various influence factors, such as the relative stiffness between the pile and the surrounding soils, taper angle, the diameter of the enlarged pile tip and stiffness ratio between the bearing soil and the overburden soil. In addition, performance of belled wedge pile within a group is evaluated in terms of the influence of pile position and pile spacing. The numerical parametric study results reveal that belled wedge pile is one of the cost-effective pile systems, which can improve vertical load carrying capacities under both compression and uplift loads and reduce the amount of negative skin friction developed due to the surcharge loads at the ground surface.

Keywords:

• pile group
• load carrying capacities
• soil–pile interaction
• dragload
• downdrag
• numerical analysis

Acknowledgements

The authors acknowledge the financial support from the National Science Foundation of China (No. 51008116, 51278170), 111 Project (No. B13024), and the National Science Joint High Speed Railway Foundation of China (No. U1134207).