## 3 Review of the Design Codes
### Pile Foundation Design
The design resistance of a pile foundation is determined using the following equation:  
\[\mathrm{R_{cid}}=\frac{\mathrm{R_{b;k}}}{\gamma_{\mathrm{b}}}+\frac{\mathrm{R_{ s;k}}}{\gamma_{\mathrm{s}}} \tag{4}\]  
where \(\mathrm{R_{b;k}}\) and \(\mathrm{R_{s;k}}\) are the characteristic values of base and shaft resistance, respectively (kN); \(\gamma_{\mathrm{b}}\) and \(\gamma_{\mathrm{s}}\) are partial factors of base and shaft resistance, respectively, for driven piles, provided in Table 3.  
The characteristic values of base and shaft resistance can be obtained using the following equations:  
\[\mathrm{R_{b;k}}=\mathrm{A_{b}}\mathrm{q_{b;k}} \tag{5}\]  
\[\mathrm{R_{s;k}}=\sum\mathrm{A_{s;i}}\mathrm{q_{s;i;k}} \tag{6}\]  
where \(\mathrm{q_{b;k}}\) and \(\mathrm{q_{s;i;k}}\) are the characteristic values of unit base and shaft resistance, respectively (kN/m\({}^{2}\)); \(\mathrm{A_{b}}\) is the pile base area (m\({}^{2}\)); and \(\mathrm{A_{s;i}}\) is the pile shaft area in the \(i\)th soil layer (m\({}^{2}\)). The limit state analysis adhering to Eurocode 7 requires the following condition to be satisfied:  
\[\mathrm{V_{d}}\leq\mathrm{R_{d}} \tag{7}\]  
where \(\mathrm{V_{d}}\) is the vertical load acting on the foundation (kN) and \(\mathrm{R_{d}}\) is the design bearing resistance (kN). Eurocode 7 provides different design approaches (DA1-1, DA1-2, DA2, and DA3) for the design of buildings and structures indicated in the National Annexes. The distribution of design approaches in EU countries for the design of pile foundations is summarized in Figure 3. The selection of design approaches by the countries is explained by their construction traditions and experience [20]. The combinations of partial factors on actions (A), material properties (M), and resistances (R) for all design approaches are given in Table 4. DA1 and DA3 are based on the Material Strength Design (MSD) method and apply partial factors on actions and material strength parameters either simultaneously or \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Design Approach**} & \multicolumn{2}{c}{\(\gamma_{\mathrm{G}}\)} & \multicolumn{2}{c}{\(\gamma_{\mathrm{Q}}\)} & \multirow{2}{*}{\(\gamma_{\mathrm{c}^{\prime}}\)} & \multirow{2}{*}{\(\gamma_{\mathrm{\varphi^{\prime}}}\)} & \multirow{2}{*}{\(\gamma_{\mathrm{b}}\)} & \multirow{2}{*}{\(\gamma_{\mathrm{s}}\)} \\ \cline{2-2} \cline{5-8}  & **Unfav.** & & & & & & & & \\ \hline DA1-1 & 1.35 & 1.0 & 1.5 & 0 & 1.0 & 1.0 & 1.0 & 1.0 \\ \hline DA1-2 & 1.0 & 1.0 & 1.3 & 0 & 1.25 & 1.25 & 1.0 & 1.0 \\ \hline DA2 & 1.35 & 1.0 & 1.5 & 0 & 1.0 & 1.0 & 1.1 & 1.1 \\ \hline DA3 & 1.0 & 1.0 & 1.3 & 0 & 1.25 & 1.25 & 1.0 & 1.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Partial factors for geotechnical Ultimate Limit States. separately. However, DA2 applies partial factors on actions and resistance simultaneously. This approach represents a method similar to Load and Resistance Factor Design (LRFD), widely applied by American codes of practice [21]. The value of the design vertical load acting on the foundation is determined in accordance with Equation (8):  
\[\mathrm{V_{d}}=\gamma_{\mathrm{G}}*(\mathrm{W_{Gk}}+\mathrm{G_{k}})+\gamma_{ \mathrm{Q}}*\mathrm{Q_{k}} \tag{8}\]  
where \(\mathrm{G_{k}}\) and \(\mathrm{Q_{k}}\) are the characteristic permanent and variable loads, respectively (kN); \(\mathrm{W_{Gk}}\) is the foundation self-weight (kN); \(\gamma_{\mathrm{G}}\) and \(\gamma_{\mathrm{Q}}\) are the partial factors on permanent and variable loads, respectively, provided in Table 3.  
When adhering to the European approach, the elastic settlement of a single pile can be determined based on elastic theory using Equation (9) [22]:  
\[\mathrm{s}=\frac{\mathrm{P}}{\mathrm{dE_{s}}}\mathrm{I_{P}} \tag{9}\]  
where P is the load acting on the foundation (kN); d is the pile diameter (m); \(\mathrm{E_{s}}\) is the Young's modulus of the soil (MPa); and \(\mathrm{I_{P}}\) is the pile displacement influence factor.