## 6 Discussion and Conclusions  
Allowing for the rocking of wind turbine foundations supported on clay, i.e., by relaxing the uplift restrictions of the conventional design practice for wind turbine foundations, is investigated. An efficient non-iterative von Mises constitutive model is integrated with the ABAQUS finite elements software and is used to simulate the behavior of undrained clay. The following observations and conclusions are made based on the finite element modeling results:  
* The non-iterative von Mises constitutive model with non-linear kinematic hardening successfully simulates the dynamic shaking of a rocking foundation on undrained clay. * A cohesive contact model that allows for limited suction between the foundation and soil results in a more accurate prediction of rotations and settlements of a rocking foundation on undrained clay, as compared to a zero-tension contact. * A foundation designed for a 5 MW wind turbine is demonstrated to safely support operational and seismic loads from a larger 8 MW wind turbine. The foundation experiences limited uplifts under the operational loads of the 8 MW wind turbine, which does not conform to the current design practice of wind turbine foundations. However, departure from the zero-uplift rule for operational conditions does not cause any safety or serviceability concerns, since the tilting of the foundation does not exceed its allowable limits, and there is no instability or excessive settlement. Further analyses with the long-term stiffness degradation of the soil also confirm this observation. * The residual tilting of the foundation under the seismic shut-down loads of the larger 8 MW wind turbine stays under the safe limit, and the width of the uplift area remains under 25%. Thus, there is not enough evidence to suggest allowing uplift areas wider than 25% of foundation width under extreme loads. * Shear failure occurs only locally near the edges of the foundation, and no instability occurs during the operational conditions or earthquake events with all the wind turbines analyzed in this research. * Finite element analysis results suggest that a further increase in the wind turbine capacity to 10 MW leads to the tilting of the foundation in operational conditions and residual tilting in seismic shut-down events to exceed the 0.25\({}^{\circ}\) limit. This indicates that there is a limit to capacity increase by allowing for a foundation uplift in operational conditions. Here, an uplift width of 4.7% of the foundation diameter was shown to be safe, while an uplift width of 15.7% of the diameter causes unacceptable tilting. The case presented in this paper is meant to be an example of this concept. The exact size of uplift area to be allowed under operational loads can be determined for any specific wind turbine, foundation geometry or soil using the method of modeling described in this paper. Allowing the foundation to experience uplift movement under operational loads makes it possible to use foundations designed for a specific wind turbine capacity to support higher-capacity (larger) wind turbines. Such a concept can be used for repurposing existing wind turbine foundations to install larger-capacity new wind turbines. Future research will establish the limits of foundation uplift for different types of cohesive soil that have different responses to cyclic loading. There is a need for experimental data for rocking foundations on mixtures of clay, silt and sand, and structured soils like glacial till. Currently, most of the available experimental data are for rectangular rocking foundations, which are used for bridge piers and shear walls. Therefore, more open-access experimental data are needed for circular rocking foundations that are used for wind turbines. Subsequently, extensive numerical modeling can be conducted to investigate the rocking of circular foundations on different cohesive soils. **Author Contributions:** Conceptualization, M.H.E.N. ; methodology, B.B.A. and M.H.E.N. ; software, B.B.A. ; validation, B.B.A. ; formal analysis, B.B.A.