Raft foundations with piles for settlement minimization: design optimization and case studies

Francesco Iorio

Studio Iorio

Antonio Sibilia

SPEA Ingegneria Europea


In the past few years, thanks to improved experimental knowledge and the use of reliable non linear geotechnical software (available both in the university and in professional practice), hybrid foundations (r.c. slabs designed for Ultimate Limit States and piles used only for settlements in Serviceability Limit States) have been widely used for tall buildings. The saving in the number and depth of piles (if designed only for settlement, it involves a limited quote –not more than 60% -70% - of the whole building loads), it is often significant compared to the overall cost of the structures (up to 10%). The design of this kind of foundation is, on the other and, strongly sensitive to the reliability of the geotechnical model used. In this publication, the design of some tall buildings in Italy and abroad is described (from the modeling of a single driven pile, to the interaction between piles and between piles and the foundation slab). Moreover, a comparison is made with experimental results of a recently completed high-rise tower (Isozaki tower in Milan). Lastly, a preliminary design of a tower in Erbil (Iraq) is shown, in which the control of settlements is related to the surrounding buildings (already existing and without deep foundations): a typical issue in the rapidly expanding city of Middle East and Asia in general.