CENTRIFUGE MODELING OF TAPERED PILES IN SAND

An experimental study was performed to investigate the performance of tapered and cylindrical piles driven into loose sand using the geotechnical centrifuge located at C-CORE, Memorial University, Newfoundland. Twelve open-ended model piles with different configurations, instrumented externally along the shaft, were successfully installed and load tested using the facility. The piles were driven at 1 g, and the loading tests were conducted at 10 g. The paper discusses the design of model piles and details of loading equipment and presents the results of axial compression tests. The results obtained showed that modeling tapered and cylindrical piles with different length-to-diameter ratios was successfully achieved. The external instrumentation technique used in this study proved to be efficient. The surface ronghness effect was found to be important and must be considered when interpreting the test results. The raining technique used in this study produced reasonably uniform soil samples. It was found that as the taper angle increased the shaft resistance increased, and the shaft resistance of the tapered pile was up to 185 % larger than that of the equivalent cylindrical pile. It was also found that the values of the combined shaft resistance factor β for cylindrical piles were consistent with Canadian Foundation Engineering Manual (1992) guidelines. In the case of tapered piles, β values were found to be 80 % higher than those for cylindrical piles, whereas the CFEM design guidelines suggest they should be 30 to 50 % higher. The effect of the taper established from experimental results compared well with the results obtained from an analytical solution based on cavity expansion theory.

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