5. Conclusion
A geotechnical design optimization procedure for a piled-raft foundation to support a tall wind turbine on clayey and sandy soil is presented in this paper. The procedure can be easily extended to the geotechnical design of piled-raft foundations to support other structures. The geotechnical design conducted in this study followed the analytical equations available in the literature and indicated that the final design is controlled by the differential settlement and the rotation of the foundation rather than the bearing capacity or the total settlement. The parametric study showed that for both types of soil, the design requirements can be met by increasing the number of piles, increasing the length of the piles, or increasing the radius of the raft when the wind speed is increased. For a higher undrained cohesion (in clayey soil) and a higher friction angle (in sandy soil), a smaller foundation was enough to meet the design requirements. The robust optimization procedure resulted in easy-to-use graphs, called Pareto fronts, which show a clear trade-off relationship between the cost and the standard deviation of the responses (differential settlement) for both soils. Although these graphs can be utilized to select the suitable design for a given set of performance requirements (variation in differential settlement) and cost limitations, the most suitable design solution is determined using the knee point concept.
