Performance- and cost-based robust design optimization procedure for typical foundations for wind turbine

A cost- and performance-based robust design optimisation procedure considering the uncertainties in soil properties and wind speed for three typical foundations (raft, pile group and piled raft) for tall wind turbines on clayey and sandy soils is presented in this paper. From the conventional geotechnical designs, it was found that the design is controlled by differential settlement and therefore considered as the response of concern in the robust design optimisation. The robust design optimisation was performed using Non-dominated Sorting Genetic Algorithm II coupled with Monte Carlo simulation to systematically incorporate the uncertainties in the soil properties and wind speed that have a direct impact on the lateral and moment load acting on the foundation. The total construction cost of the foundation and the standard deviation of the differential settlement were considered as the objectives of interest to be minimised. This procedure resulted in a set of acceptable designs presented in a graphical form called Pareto front for each foundation type on clayey and sandy soils. The comparison of Pareto fronts for the three foundations showed that the pile group or piled raft foundation is economical with higher robustness while the raft foundation is economical with lower robustness. Further, the optimum designs of each type of foundation on clayey and sandy soils were determined using the knee point concept from the Pareto front. The easy-to-use Pareto fronts can be used for selecting suitable foundation type and corresponding design variables for a given performance and cost limitations.