Uplift Behavior of Belled Piles Subjected to Static Loading

Abstract

The uplift behavior of foundation is of great importance for the construction of foundations of ports, transmission towers and other structures that require to resist uplift loading. This research presents the results of several uplift static loading tests of prototypical belled piles. The load–displacement curve of belled piles is divided into three stages: initial linear segment, middle curve segment, and ending linear segment. The characteristic uplift capacities for the three stages are given by a graphics method. A bi-linear equation is given for predicting characteristic loading capacities of piles based on the ratio of bell to shaft diameters (bb/bs) and the embedment depth (L). Using the calibrated micro-parameters by the load–displacement curves, PFC2D is used to investigate the development of microcracks and formation of soil slip surface in the uplift test. The predicted uplift capacities by simulation can match the experimental value and estimated value by the suggested linear equation. The numerical result shows that the microcracks propagate, connect, and coalesce rapidly once the load–displacement curve reaches the middle curve segment. The final soil slip surface from numerical simulation varies with the geometric dimension of belled piles. The effect of bell to shaft diameters ratio (bb/bs) and embedment depth (L) on the uplift capacity is examined using numerical uplift tests. The result shows that uplift capacity of belled piles can be improved by increasing bell to shaft diameters ratio (bb/bs) and embedment depth (L).