3D nonlinear finite element analysis of piled-raft foundation for tall wind turbines and its comparison with analytical model

Geotechnical design of piled-raft foundation is typically performed using simplified semi-empirical equations that do not consider the interaction between structural components and supporting soil and the effect of bending moment on the differential settlement of piled-raft. In this study, the settlements and rotations computed using an analytical and linear and nonlinear finite element methods were compared. First, a piled-raft foundation for supporting a 130 m-tall wind turbine was designed using simplified analytical method and then a nonlinear finite element model was created in ABAQUS and analyzed. In the finite element modeling, the stress-strain behavior of the soil was represented by linear elastic (LE) and nonlinear elastoplastic Drucker-Prager (DP) models. The interfaces between structural components and soil were modeled as two bodies in the contact that allows slipping and separation at the interfaces. The results showed that the vertical and the horizontal displacements from the analytical procedure were significantly higher than that of the nonlinear finite element method. At the same time, the differential settlement and rotation were lower than that of ABAQUS. The parametric study conducted by varying the wind speed and undrained shear strength of the soil indicates that the difference between the predicted responses decreases when the load is large and/or soil is soft. From the finite element analyses, it was observed that the separation and slip between the soil and pile were negligible. It was also found that the piles contributed more in reducing vertical settlement, raft contributed more in reducing horizontal displacement, and only piles were contributing to reduce differential settlement. © 2020, Taiwan Geotechnical Society.