Settlement analysis of piled-raft foundations by means of a multiphase model accounting for soil-pile interactions

The behavior of vertically loaded raft foundations, strengthened by a large group of floating piles, is investigated by means of a multiphase approach, where special emphasis is put on the ground-pile interactions, which play an important role on the foundation performance. A new specific interaction law relating to the pile tip resistance is incorporated into the multiphase model, in addition to that already developed for pile shaft friction in a previous version. A numerical identification procedure is presented, which allows evaluation of the stiffness and yield strength parameters governing such interaction laws, as functions of the different geometric characteristics defining the pile layout (pile diameter and spacing), along with the material constitutive properties of the soil, modeled as a purely cohesive clay. The improved multiphase model, implemented in a finite element code, is used to analyze the response of a square raft lying upon a group of piles, varying the pile number and pile length. A relatively good agreement is obtained between the results of this approach, expressed in terms of load-settlement behavior as well as pile force distributions, and those derived from direct computationally intensive finite element calculations, where piles are regarded as individual elements embedded in the soil.