Optimization of the Piled-Raft Foundations Considering the Soil-Pile-Raft Interaction

In comparison to the conventional piled foundations, the piled-raft foundations provide a more economical solution to support high-rise buildings constructed on soft soils. In this type of foundations, the bearing capacity of the underlying soil is taken into account to support the superstructure loads and the piles are placed to control both the total and differential settlements of the superstructure. Currently, there is not a standard and worldwide acceptable approach to select the location of the piles and most of piled-raft foundations are designed based on the experience of designers. Therefore, particular attention should be given to the optimal design of this type of foundations in order to minimize the considerable construction costs involved. This paper examines the capability of the ant colony optimization (ACO) algorithm to optimize the piled-raft foundations subjected to static and seismic loadings. The soil-pile interaction is considered by modeling the side and tip resistance components of the piles using the nonlinear Winkler-based p-y and t-z curves in the OpenSees program. The soil-raft interaction is taken into consideration using the Winkler springs beneath the raft. The objective of the optimization problem is to minimize the construction cost of the foundation by taking the configuration and number of the piles as design variables. The side and tip forces of the piles as well as the total and differential settlements of the foundation under the serviceability limit state are considered as the constraints for the optimization problem. Results show that in addition to the type of analysis (linear/nonlinear), the regard or disregard of the soil-pile interaction in the analysis can significantly change the optimal solution. The optimal solutions obtained match the engineering expectations and indicate the effectiveness and capability of the ACO algorithm to minimize the construction cost.