In this project, a series of centrifuge tests were conducted to study the behavior of single jacked-in piles and pile groups in both loose (relative density, D_r = 42%) and dense (relative density, D_r = 73%) sands. Interaction effects of both free-standing pile groups and pile groups with cap-ground contact were studied. At failure, both the shaft and base resistance were fully mobilized with pile head settlement exceeding 30% of the pile diameter (0.3m). The measured β values for the single pile tests in loose sand and dense sand are 0.3 and 0.56, respectively. While for the pile group tests, the measured β values for the group piles are generally the same with each other. In loose sand, the measured β values for freestanding and cap-ground contact groups are 0.6 and 0.5, respectively....[ Read more ]

In this project, a series of centrifuge tests were conducted to study the behavior of single jacked-in piles and pile groups in both loose (relative density, D_r = 42%) and dense (relative density, D_r = 73%) sands. Interaction effects of both free-standing pile groups and pile groups with cap-ground contact were studied. At failure, both the shaft and base resistance were fully mobilized with pile head settlement exceeding 30% of the pile diameter (0.3m). The measured β values for the single pile tests in loose sand and dense sand are 0.3 and 0.56, respectively. While for the pile group tests, the measured β values for the group piles are generally the same with each other. In loose sand, the measured β values for freestanding and cap-ground contact groups are 0.6 and 0.5, respectively. In dense sand, the measured β values for both freestanding and cap-ground contact groups are 0.6.

Group efficiency factors were calculated using different failure criteria. It is clear that the total group efficiency values for piles jacked in loose sand interpreted using various failure criteria differ significantly while the values for those piles in dense sand do not differ considerably. The Davisson's failure criterion predicts total group efficiency values of 1.9 and 1.5 in loose sand for the free-standing pile groups and the cap-in-contact pile groups, respectively. These set of values are the highest among all the failure criteria. For other criteria, the total efficiency values range from 1.1 to 1.3. In dense sand, the total efficiency values within a narrow range from 0.8 to 1.1 regardless of the failure criteria. Depending on the selection of failure criteria, it is revealed that the shaft efficiency for loose sand ranges from 2.7 to 1.6 and 1.6 to 1.3 for free-standing and cap-in-contact pile groups respectively. In contrast, the shaft efficiency varies from 0.8 to 1.0 for dense sand. The improved in shaft efficiency in loose sand is probably due to densification of the soil in the pile groups. The point efficiency for piles in loose sand generally ranges from 0.8 to 0.9 and 0.6 to 0.7 for free-standing and cap-in-contact pile groups respectively. For dense sand, similar results as concluded by Vesic (1968) were obtained where the point efficiency value are also close to 1.0.