## 3 Results  
### Matrix Suction and Soil Water Characteristic Curve  
This study focuses on the Whatman No. 42 filter paper method, according to ASTM D5298, for measuring suction at previously specified moisture content. This method requires numerous precautions regarding the ambient temperature and humidity, accuracy of the water content measurement of the filter paper, and a calibration curve relating the absorbed water to suction for a specific filter paper type [61]. Figure 11a-d illustrates the filter paper employed and its placement within the soil sample, following the specifications of the referenced standard. Each sample was then stored in airtight glass jars for seven days to allow water redistribution between the soil and filter paper until thermodynamic equilibrium was reached. This storage also prevented microbial activity and minimized suction fluctuations due to changes in the relative humidity and temperature, which could otherwise affect the samples. The storage location was in the north-central area of Quito, and laboratory testing was conducted within the same month as the sample collection in June. According to [PERSON] [40], the site experiences temperature fluctuations between 5 \({}^{\circ}\)C and 26 \({}^{\circ}\)C during June; consequently, samples were stored in isothermal containers made of expanded polystyrene, which controlled temperature variations within \(\pm\)3 \({}^{\circ}\)C and were continuously monitored using a thermohygrometer. The procedure and apparatus are illustrated in Figure 11e-f, respectively. The results are summarized in Tables 9 and 10. Figure 9 presents the data points obtained from the particle size distribution test, along with the theoretical curve fitted using the adapted Fredlund and Xing model. The results demonstrate an excellent fit, as evidenced by the high R\({}^{2}\) value and smooth curve profile, which shows no abrupt transitions or trends, suggesting the presence of multiple slopes or plateaus. These observations support the interpretation that the soil exhibits a unimodal particle size distribution, which in turn implies a corresponding unimodal pore size distribution. Therefore, the application of a unimodal model, such as the Fredlund and Xing model, is a good fit to the data. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Depth [m]** & **LL [\%]** & **LP [\%]** & **IP [\%]** & **Gravel Fraction [\%]** & **Sand Fraction** & **Fine Fraction** \\  & & & & & **Fraction [\%]** & **[\%]** & **[\%]** \\ \hline
1.00 & 43 & 34 & 9 & 0 & 35 & 65 \\
2.00 & 54 & 42 & 12 & 0 & 32 & 68 \\
3.00 & 41 & 37 & 4 & 1 & 33 & 66 \\
4.00  
Xing equation, for determining the Soil Water Characteristic Curve (SWCC) is considered appropriate. The fitting parameters used in the model are presented in Table 11. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Depth [m]** & \begin{tabular}{c} **Water** \\ **Content [\%]** \\ \end{tabular} & \begin{tabular}{c} **Gravimetric** \\ **Water Content** \\ \end{tabular} & \
\begin{tabular}{c} **Matrix Section** \\ **[kPa]** \\ \end{tabular} &
\begin{tabular}{c} **Saturation [\%]** \\ \end{tabular} \\ \hline
2.00–2.50 (1) * & 33.81 & 0.45 & 19.22 & 93.97 \\
2.00–2.50 (2) & 32.89 & 0.43 & 55.01 & 91.39 \\
4.00–4.50 & 21.48 & 0.25 & 38.72 & 52.45 \\
5.00–5.50 (1) & 33.58 & 0.42 & 29.10 & 87.66 \\
5.00–5.50 (2) & 33.41 & 0.44 & 22.92 & 92.14 \\
6.00–6.50 & 30.48 & 0.44 & 5.34 & 92.39 \\
7.00–7.50 (1) & 28.27 & 0.38 & 5.97 & 79.16 \\
7.00–7.50 (2) & 29.13 & 0.39 & 3.89 & 81.58 \\
8.00–8.50 (1) & 29.46 & 0.46 & 4.32 & 96.77 \\
8.00–8.50 (2) & 28.69 & 0.45 & 5.96 & 94.23 \\ \hline \hline \end{tabular}  
* Numbers in parentheses (1)–(2) denote replicate measurements performed at the same depth to evaluate repeatability and data consistency.  
\end{table} 
Table 10: Undisturbed sample suction properties. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **Value** \\ \hline \(\psi_{\text{r}}\) & 50 \\ \(\theta_{\text{s}}\) & 0.475 \\ a & 12 \\ n & 1.1 \\ m & 0.34 \\ \hline \hline \end{tabular}  
\end{table}