Development of a multiple pile driver/load test device for pile group studies: Fid-Bau Portal

Development of a multiple pile driver/load test device for pile group studies

Bloomquist, D. / Feld, T. / Townsend, F.C. / Gravgaard, J. / Gill, J.

During the past several years, a substantial amount of effort has been expended developing miniature pile driving devices for use in the University of Florida's 1.6 m centrifuge. The ultimate goal of this endeavor was to devise equipment that would allow a series of individual piles to be driven, using any driving sequence/spacing and then load test the group in flight without reducing the test acceleration at any time. The original driver made use of a stepping motor and electromagnet that lifted and dropped a weight unto the pile. By keeping track of the number of steps, the unit could follow the pile during driving thereby maintaining a constant drop height. Comparison between in-flight driven and 1 g statically pushed piles showed a marked difference in capacity - indicating the importance of in-flight placement in sands. It was subsequently discovered that if a pile was 'driven' into the soil using the stepping motor directly, similar load capacities compared to the weight drop technique were obtained. Thus, the distinct steps of the motor, operating at 50 Hz, appears to limitate a diesel hammer. From these results, the current device makes use of a stepping motor to step-drive a series of 5 piles in any group configuration/driving sequence and to then load test the group in flight. Load tests on both single and group model piles reveal group capacity efficiencies of 80 %, and that driving the center pile last of a group produces higher capacity.