Physical Modeling of Raft on Settlement Reducing Piles

The paper presents the results of extensive centrifuge tests modeling rigid circular piled rafts laying on a bed of loose very fine silica sand. The tests were aimed at investigating the behavior of rafts on settlement reducing piles. The testing program included: an unpiled raft, rafts on 1, 3, 7 and 13 piles. In each test, some model piles were instrumented with load cells to determine the distribution of load along the shaft. Beneath the rafts, two types of model piles, close-ended and free headed were installed: quasi displacement (QD) and quasi-non displacement (QND) piles. The obtained results permitted figuring out the role of piles in terms of their effectiveness as settlement reducers and to quantify the load sharing mechanism between piles and the raft-soil contact. The tests were aimed at investigating the load transfer mechanisms adopted in the design approach, and in particular at validating a numerical code which can be used in engineering practice. The paper describes the details of experiments undertaken, the adopted procedures and some of the results; where not specified, all the experimental data given in this paper referred to model scale. The adopted numerical code is briefly described and its validation, via test results on quasi-non displacement piles, is also reported.