A preliminary soil-raft-piles interaction analysis for the New Law Court in Florence

The New Law Court complex in Florence, at present under construction, consists of buildings that are of different heights, with a maximum of 77 meters from g.l. It covers a surface of about 30.000 m2, and has a total volume of 750.000 m3, about 550.000 m3 of which are in elevation. The foundation soil is part of an alluvial deposit composed mainly of over-consolidated silty clay with local and frequent lenses and inclusions of pebbles, gravel and calcareous nodes in a clayey silty matrix. In view of the importance of the work, numerous geotechnical surveys have been carried out, both in situ and in the laboratory, and studies on specific topics have been developed. Among these is an analysis of the soil-raft-piles interaction. The structural loads transferred to the foundation soil are variable and not uniform and. Therefore, the main geotechnical problem involves the absolute and differential settlements under working conditions. The foundation system consists of a piled raft situated 7 meters down from g.l. Two procedures have been used in the pile group design: the traditional, conservative method, which assumes that the total structural load is carried by the piles, and the "new" method, which assumes that the raft is in direct contact with the soil and evaluates the number of piles required for settlement reduction. The two solutions are compared both in terms of number of piles, i.e. from an economical point of view, and in terms of expected absolute and differential settlements of the foundation raft.