Centrifuge tests on the consolidation behaviour of foundations under alternating loads

This paper presents the results from centrifuge tests on raft foundations and piled rafts in overconsolidated kaolin clay carried out in a beam centrifuge at the University of Pretoria. The foundations were subjected to unloading and reloading phases as well as to multiple consecutive groundwater drawdowns, simulating typical loading scenarios of structures in an urban environment. In order to investigate the time-dependent load-deformation behaviour of foundations, the settlement of the foundations, the pore water pressures at different depths and the axial strains in the piles, from which pile resistances were then derived, were measured continuously. In the tests, repeated groundwater drawdowns resulted in a settlement accumulation, with the increase in settlements decreasing with each repetition. The pile position within the pile group was found to have a major impact on the mobilised pile resistance. The position, however, became less significant as the load level increased. Furthermore, insights were gained concerning the load distribution within piled rafts during consolidation.