Combined –Piled –Raft-Foundation (CPRF) systems are often suitable for foundations of high-rise buildings to reduce the excessive settlement of foundations. The conventional design of the pile group foundation, loads are designed to be transferred via the piles to the soil neglecting the contribution of the raft. In the last decades, geotechnical engineers have started to design the piled raft foundation more optimized by allowing a part of the pressure to transfer directly from the raft to the ground. Piled raft foundations have a complex soil-structure interaction particularly when weak layered soils are encountered. This often requires the use of advanced numerical methods. In this research, the objective is to study the settlement characteristics of piled raft foundation on a weak layered soil in which detail literature study were undertaken, a 3D numerical FEM based model were developed, sensitivity/ convergence analysis of the different factors were studied and finally the parametric study of pile length, pile diameter, pile spacing and raft thickness factors were performed. The raft and piles were modeled with a linear elastic constitutive model whereas; the soil continuum was modeled with both elastic and Mohr-Coulomb plasticity constitutive models. The results of the analyses show that the differential settlement does not change significantly after a raft thickness of 1.5 m; this thickness was taken as a good fit for this foundation in terms of cost. In order to develop a cost effective foundation with minimum total and differential settlement, an optimization among the pile length, diameter and spacing should be established. A parametric study was carried out by using geotechnical finite element software, ABAQUS to investigate the influence of various parameters on the relationship of settlement reduction factor (𝜉𝑠) which is calculated as the ratio of settlement of combined piled raft foundation to that of unpiled raft for the midpoint of the raft and the normalized load. For pile spacing and raft thickness the application of combined piled raft foundation is more effective up to a certain load level (700 kPa) which is equivalent to a normalized value of 0.33. And for pile length and pile diameter the normalized optimal load level becomes 0.22 which is equivalent to 450 kPa. Another parametric study has been conducted to see the effect of weak layer located below the raft on the settlement reduction factor (ξs) relative to midpoint of the raft. Based on the results, it can be concluded that for all stiffness ratios (0.14 to 0.9) considered in this study, the piled raft behavior is not affected if the weak stratum is located below 18 m and the effect is negligible for relative stiffness of the weak layer to the stiffness of the soil layer below the raft greater than 0.6.