El Naggar, MH
Assistant professor and research director, Geotechnical Research Centre, Faculty of Engineering Science, The University of Western Ontario, London, Ontario
Engineer-in-training, Pipe Integrity, TransCanada PipeLines, Calgary, Alberta
(Received 15 June 1998; accepted 3 September 1999)
Tapered piles have a substantial advantage over straight-sided wall piles with regard to their load-carrying capacity in the downward frictional mode; however, their behavior under cyclic axial loading has not been investigated. In this study, the characteristics of the cyclic response of tapered piles were established from experimental investigation. A large laboratory facility for testing model piles was developed. In this facility, the soil was contained in a steel chamber and pressurized using an air bladder to model the confining pressure. Three instrumented steel model piles with different degrees of taper were installed in loose sand and subjected to two-way cyclic axial load tests. The results of this study indicated that the pile stiffness under cyclic loading increased with an increase in the confining pressure for all piles examined in this study. Moreover, the pile stiffness increased through cyclic loading due to the densification of the sand surrounding the pile. The amplitude of the cyclic load had a significant effect on the performance of the piles. As a result, it is recommended that the amplitude of the cyclic load be limited to 25% of the static axial capacity and 75% of the static uplift capacity to ensure satisfactory performance of tapered piles. This requirement is readily satisfied in the design of most piles. In this case, the performance of tapered piles under cyclic axial load was found to be superior to that of straight-sided wall piles.
Paper ID: GTJ11128J