A study on optimization of piled rafts

In this study, optimum design principles of piled rafts are investigated using settlement based design approach. Settlements are calculated using the simplified method of Randolph and finite element analysis with Plaxis 3D software. Load sharing between the raft and pile group is taken into account in Randolph method, since the contribution of raft to load carrying capacity of the overall foundation system is the basis of piled raft approach. A case study is introduced in order toreach an optimum solution in terms of settlement based design. Optimum design is investigated in two stages. In the first stage, effect of number of piles on settlement behaviour of piled rafts is investigated. The aim of first stage is to reach an economical solution. In the second stage, total pile quantity is kept constant and it is aimed to seek satisfactory behaviour in terms of settlements.It is shown that the optimum solution may be reached by increasing pile length rather than number of piles. Stiffness of a pile group is not equal to sum of single pile stiffness due to the interaction among piles. Group efficiency coefficient is used for taking into account the interaction effect and an emprical equation is suggested for efficiency factor. The proposed equation consists of an interaction term and non-linearity term which are based on Randolph and Caputo&Viggianiapproaches, respectively. Validation of the suggested equation is investigated by comparing with the results of two case studiesthat field measurements are available in the literature.It is shown that settlements estimated by means of the suggested equation are in good agreement with the measured values.