## 2 Method
These cores were collected from foundations that exhibited  
Figure 3: Photos of the construction of the foundations, (**a**) after placing the reinforcement, (**b,c**) during casting of the concrete, and (**d**) the completed foundation before backfilling with soil. surface cracking, when the foundations were between less than a year old and up to approximately three years old. On a few foundations, the top concrete layer was removed locally using high-pressure water jetting for additional inspection and to remediate localised defects (see Figure 4d). For the purpose of this study, data were gathered from technical documents and drawings from the design stage; daily logs from the construction stage; and photos, inspection, and measurement reports from the inspection stage. When needed, complementary information was obtained through personal communication with persons involved in these different stages. A method used to evaluate the extent of the defects on single foundations was defined in this work based on the information available and its level of accuracy. The different types of defects that were evaluated are detailed in Table 1, which forms the basis of the assessment method. The different types of defects assessed were then aggregated by defining defect indexes as listed in Table 2.  
Figure 4: (**a**) Measurements of the crack width using a crack comparator card, (**b**) measurement of the concrete cover using a concrete scanner, (**c**) drilling of concrete cores from the foundations, and (**d**) after water jet removal of the top concrete layer. The general defect index was defined as the sum of the crack index and the reinforcement and casting defect index:  
\[I=I_{1}+I_{2}, \tag{1}\]  
where the crack index is calculated from the underlying assessed defects \(D_{1,1-3}\), as:  
\[I_{1}=\frac{D_{1,1a}+D_{1,1b}}{2}+D_{1,2}+D_{1,3}, \tag{2}\]  
and the reinforcement and casting defect index is calculated as the sum of the defects \(D_{2,1-5}\):  
\[I_{2}=\sum_{i=1}^{5}D_{2,i}. \tag{3}\] \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Type of Defect** & **Symbol** & **Assessment Scale** & **Value** \\ \hline Number of cracks on the external & & & 0: no crack \\ inclined surfaces of the foundation & \(D_{1,1a}\) & 0–3 & 1: few cracks (\textless{}10) \\  & & & 2: several cracks (10–20) \\  & & & 3: many cracks (\textgreater{}20) \\ \hline  & & & Based on crack width measurements, \\  & & & with \(w_{\sigma\sigma}\) corresponding to the maximum \\  & & & crack width measured: \\ Size of cracks on the external & \(D_{1,1b}\) & 0–3 & 0: no crack \\ inclined surfaces of the foundation & \(D_{1,1b}\) & 0–3 & 1: \(w_{\sigma\sigma}\) \textless{} 0.4 mm \\  & & & 2: 0.4 mm \(\leq w_{\sigma\sigma}\) \textless{} 0.5 mm \\  & & & 3: 0.5 mm \(\leq w_{\sigma\sigma}\) \\ \hline  & & & 0: no crack \\  & & & 1: minor cracking \\  & & & 2: moderate cracking \\  & & & 3: severe cracking \\ \hline Radial temperature cracks at the periphery & & & 0: no observation of cracks \\  & of the foundation and & \(D_{1,3}\) & 0–1 & 1: observation of cracks \\ extending on the inclined surface & & & & \\ \hline  & & & 0: sufficient concrete cover \\  & & & 1-3: insufficient concrete cover: \\  & & & 1: at less than 6 locations \\  & & & 2: at 6–10 locations \\  & & & 3: at more than 10 locations \\ \hline Incorrectly installed reinforcement & \(D_{2,2}\) & 0–1 & 0: no observation of wrong placement \\  & & & 1: observation of wrong placement \\ \hline  & & & Based on visual inspection: \\ General finish aspect of the concrete surface & \(D_{2,3}\) & 0–1 & 0: good surface finish \\  & & & 1: irregular surface finish \\ \hline Casting too high relative to & & & 0: no observation of problem \\ the tower anchor bolts & \(D_{2,4}\) & 0–1 & 1: observation of problem \\ \hline Other localized casting defects & & & 0: no observation of problem \\  & under the soil level & \(D_{2,5}\) & 0–1 & 1: observation of problem \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Defects assessed on the gravity-based foundations.