Influence of Pile-Soil-Raft Parameters on the Behavior of Piled Raft and Conventional Piled Group Foundations

Abstract

In the Central Area of Brazil, particularly in the city of Goiânia (and in limited cases of the Brazilian capital Brasília), it is becoming common to observe in few foundation projects the design of a single, thick and large raft, supported by several piles, particularly for the central highly loaded and slender part of very tall buildings. In fact, many of these piles are designed as “settlement reducer” ones, behaving as “floating piles” with distinct geometries or relative pile stiffness (pile-soil) ratios. They are defined with basis on some rationalized procedure adopted to minimize the differential and total settlements of the raft, also based on its relative raft stiffness (raft-soil) together with aforementioned aspects. In such conditions, the calculation is usually done using a capacity and settlement based design approach that is normal in the case of “piled raft” foundation systems. Therefore, this paper aims to investigate this particular topic, scrutinizing numerical results of piled raft cases (and its comparison with “conventional” pile groups) under both cases of horizontal and vertical load conditions. It focuses on the influence of some key parameters of piled raft systems (related to overall pile, soil and raft geometric & mechanical characteristics) on their hypothetical design behavior. It further explores the possible advantages of designing under the concept of piled rafts under few particular conditions, yielding generalized conclusions from a “practical” point of view for those interested in such design methodology.