Geotechnical Design and Design Optimization of a Pile-Raft Foundation for Tall Onshore Wind Turbines in Multilayered Clay

Abstract

Although the pile-raft foundation is preferred for supporting a tall wind turbine, the geotechnical design and selection of suitable design parameters are based on a complex procedure. Except the foundation, all the other aboveground components are precast members that are assembled at the project site to build a wind turbine. Therefore, it is necessary to consider the possible variations in soil properties and wind speed in the design of the foundation. In this paper, a reliability-based robust design procedure for a pile-raft foundation that supports a 130-m-tall wind turbine on a layered clayey soil is presented. Upon completion of the geotechnical design for the mean wind speed and undrained shear strength, a parametric study and Monte Carlo simulation were conducted by varying the wind speed and the undrained cohesion of each layer to establish a relationship among the design variables (number and length of piles and radius of the raft) and the random variables (wind speed and undrained cohesion). Finally, a reliability-based robust design was created considering the total cost and robustness as the objectives. The standard deviation of the response of concern, which is the differential settlement, was considered the measure of robustness. The optimization yielded a set of preferred designs known as the Pareto front, and the suitable design was selected for a given cost limitation and performance requirement using the Pareto front.