Design charts for elastic pile shortening in the equivalent top-down load-settlement curve from a bidirectional load test
With a rigid pile assumption, the equivalent top-down load-settlement curve constructed from the results of a bidirectional or bottom-up pile load test does not fully consider the total elastic shortening when all the load components from skin-friction and end-bearing are applied downward at the pile head. In effect, the equivalent curve constructed by the original method suggested from the Osterberg test showed a much stiffer curve compared to the top-down curve. Design charts are provided in this paper from the results of a parametric study on bored piles in order to approximately evaluate the lambda-factor that is used to estimate the top-down pile shortening from the bottom-up shortening due to the skin-friction component of the load. It has been shown that the lambda-factor varies with the distribution of the undrained shear strength profile, pile slenderness ratio, and mobilization of the skin-friction resistance. In addition, the pile shortening due to the end-bearing load component is added to the top sett lements by treating the pile as an elastic column. A modified method for the construction of the equivalent top-down load-settlement curve is presented that considers the elastic pile shortening and validated with the measured top-down load-settlement curve from pile load tests. (C) 2010 Elsevier Ltd. All rights reserved.
elastic pile shortening bidirectional test osterberg (o-cell) test bottom-up test top-down test equivalent load-settlement curve