## 5 Results  
This section presents the results of FE analyses conducted to evaluate the effects of the foundation uplift on the soil and displacements of the foundation. The extent of uplift under operational and seismic shut-down conditions is increased by increasing the size of the WT installed on the foundation. Figure 11 displays the contours of contact pressure under the foundation supporting the 5 MW WT. The white regions in the contours indicate the regions of uplift, distinguished as the regions where contact pressure is zero or negative (tension). As explained in Section 3, limited tension is allowed in the contact between the foundation and soil, to simulate the effect of suction. It is apparent that the foundation uplift region for 5 MW WT in operation has a negligible width, approximately 2% of the diameter of the foundation, almost satisfying the rule of the conventional design practice that does not allow for uplift under operational loads. Under the loads of the shut-down event due to EQs, uplift areas are narrow, with widths less than 5% of the diameter of the foundation, which is well below the 25% and 50% limits adopted by design guidelines for extreme loads. Figure 11: Uplift areas under the foundation of the 5 MW WT; **(a)** In normal operation, **(b)** Shut-down with Saguenay EQ, **(c)** Shut-down with Val des Bois EQ. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Material** & **Tower Steel** & **Foundation Concrete** \\ \hline Young’s Modulus & 210,000 MPa & 22,500 MPa \\ Poisson’s Ratio & 0.3 & 0.175 \\ Density & 8500 kg/m\({}^{3}\) & 2325 kg/m\({}^{3}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Parameters of the structural materials in WT models. Figure 12 presents the pressure distribution and uplift areas under the 8 MW and 10 MW wind turbines. It is obvious that the areas subjected to uplift under operational loads are greater for the case of 10 MW WT than for the 8 MW WT, and both clearly exceed the stated 0% tolerance for conventional WT foundation design. On the other hand, the width of the uplift area under seismic shut-down loads is less than 13% of the footing diameter for the 8 MW WT, while it is almost 50% for the 10 MW WT subjected to the Saguenay EQ. To evaluate the serviceability effects of the foundation uplift values mentioned above, settlements and rotations of the foundation are calculated based on vertical displacements of the center and edges of the foundation. Permanent settlements of the foundation (vertical displacement at the end of dynamic loading) are given in Table 6. It is evident that the settlements are small enough (less than 2 mm for the largest WT) to not cause any disruptions to the operation and accessibility of the WTs. In addition, the rotations \(\theta_{X}\) and \(\theta_{Y}\) of the foundation around two perpendicular horizontal axes, \(X\) and \(Y\), are calculated,  
Figure 12: Uplift areas under the foundation of the 8 MW and 10 MW WTs; **(a)** 8 MW WT operation, **(b)** 8 MW WT shut-down with Saguenay EQ. **(c)** 8 MW WT shut-down with Val des Bois EQ. **(d)** 10 MW WT operation, **(e)** 10 MW WT shut-down with Saguenay EQ, **(f)** 10 MW WT shut-down with Val des Bois EQ. and the corresponding tilting rotation of the foundation around the direction with the largest rotation is calculated as \(\theta_{Tilt}=\sqrt{\theta_{X}^{2}+\theta_{Y}^{2}}\). Time histories of tilting rotations of the foundations of the three considered WTs under rated operation loads are plotted in Figure 13. The tilting of the 5 MW and 8 MW WT foundations under operational loads remain under the 0.25\({}^{\circ}\) tolerance limit for both the 5 MW and 8 MW WTs, but it is slightly exceeded for the 10 MW WT. This indicates that the foundation designed for the 5 MW WT can support a larger (8 MW) WT's operational loads by allowing for a limited uplift movement, while ensuring the tilt angle remains below 0.25\({}^{\circ}\). Similarly, tilting rotations of the WT foundations are plotted for shut-down events caused by two earthquakes in Figures 14 and 15.