Volume 21, Issue 3 (September 1998)
Model Tests for Uplift Resistance of Piles in Sand
An experimental program using large model piles in sand was conducted to study the shaft resistance behavior of piles subject to uplift loads. Model single pipe piles of different diameters (45 to 178 mm) were subjected to static uplift loading to failure. The piles, which had an embedded length of about 1.7 to 2 m, were installed in a large test pit (3 by 3 by 3 m) by three different methods (driving, jacking, and a reference undisturbed method with negligible lateral displacement) to assess the influence of method of installation on shaft resistance. The tests were performed in two initial densities of a sand (loose and dense). The experimental results were analyzed statistically. The results show that the initial sand density and the method of pile installation are the most significant factors that affect uplift capacity. Installation methods that cause less disturbance give higher uplift capacity. Unit shaft resistance could be reduced as much as by half depending on the method of pile installation relative to the undisturbed method. The displacement at the ultimate uplift load is in the range of 5 to 12.5 mm and independent of soil type and pile diameter, but depends on method of pile installation.