en Soil Mechanics Classic Soil Mechanics Classic Research Paper Research Paper <p>It has been realized that the raft (mat) foundations are capable of bearing very large loads when they are assisted with a pile<br> group. The contribution of both raft and piles to carry the surcharge loads is taken into account, considering the stiffness and<br> strength of involved elements in the system, i.e. piles, raft and surrounding soil. The piles are usually required not to ensure the<br> overall stability of the foundation but to act as settlement reducers. There is an alternative design in which, the piles are nonconnected<br> from the raft to reduce the settlement, which are then known to be "settlement reducer non-connected piles" to increase<br> the system stiffness. In this paper, two and three dimensional finite element analysis of connected and non-connected pile-raft<br> systems are performed on three case studies including a 12-storey residential building in Iran, a 39-storey twin towers in<br> Indonesia, and the Messeturm tower, 256m high, in Frankfurt, Germany. The analyses include the investigation of the effect of<br> different parameters, e.g. piles spacing, embedment length, piling configuration and raft thickness to optimize the design. The role<br> of each parameter is also investigated. The parametric study results and comparison to a few field measurements indicate that<br> by concentrating the piles in the central area of the raft foundation the optimum design with the minimum total length of piles is<br> achieved, which is considered as control parameter for optimum design. This can be considered as a criterion for project cost<br> efficiency. On the other hand, non-connected piled-raft systems can significantly reduce the settlements and raft internal bending<br> moments by increasing the subsoil stratum stiffness. Finally, the comparison indicates that simple and faster 2D analysis has<br> almost similar results to the time consuming and complicated 3D analysis.</p> Piled-raft foundations (PRF), Optimized design, Connected piles, Non-connected piles, Finite element analysis 100 111 http://ijce.iust.ac.ir/browse.php?a_code=A-10-270-1&slc_lang=en&sid=1 A. Eslami afeslami@yahoo.com 180031947532846009671 180031947532846009671 Yes Associate Professor, Amir Kabir University of Technology (AUT), Tehran, Iran M. Veiskarami mveiskarami@gmail.com 180031947532846009672 180031947532846009672 No Assistant Professor, the University of Guilan, Rasht, Iran M. M. Eslami mandro.es@gmail.com 180031947532846009673 180031947532846009673 No M.Sc. Student, Sharif University of Technology, International Campus, Kish Island, Iran