Dynamic and Static Load Testing of Model Piles Driven into Dense Sand

Abstract

Systematic studies of pile response during static and dynamic load tests are generally too expensive to conduct in the field, and at model scale may be limited by scaling effects and the ability to obtain accurate stress waves. This paper describes such a study, conducted at model scale in a geotechnical centrifuge, for piles driven into dense sand. Adverse scaling effects were minimized by the use of extremely fine sand (silica flour), and accurate stress waves were obtained using high-frequency data logging, together with a Hopkinson bar arrangement for the measurement of pile-head velocity. The overall aim of the study was to compare dynamic and static test data, for open- and closed-ended piles driven into dense sand, for a range of delivered hammer energies. Open- and close-ended model piles were driven into dense sand and statically load tested at different penetrations, without stopping the centrifuge. Stress-wave data were collected, during continuous driving and from single blows immediately prior to the commencement of static load testing. An assessment of the accuracy of the mobilized soil resistance estimated from dynamic testing, using different levels of analysis, has been made by direct comparison with the static load test data. Particular emphasis has been placed on the performance of the dynamic analyses in light of different driving conditions and delivered hammer energy. From measurements of the delivered hammer energy, the efficiency of the centrifuge pile driving system was also assessed.