## 2 Materials and Methods
### Retention Curves and Conductivity Curves  
To obtain the required parameters for numerical simulation, the first step was to obtain the characteristic curve and soil conductivity of the samples under study. Therefore, the material available was initially sieved, and the fraction that was retained on the no. 10 sieve (2 mm opening) was discarded as the HYPROP (Hydraulic Property Analyzer) and WP4-C (Water Potential Four) equipment utilized for obtaining the hydraulic functions does not allow for working with material with larger granulometry.  
The HYPROP is an instrument used to measure the soil water potential at different levels of saturation, employing two tensiometers. During the experiment, the soil sample is placed on a laboratory balance, while the HYPROP records the changes in water potential resulting from water evaporation over time. Additionally, the instrument monitors the weight variations of the sample, allowing for the determination of soil moisture content. It is worth noting that the HYPROP exclusively measures the matric potential in the wet range of the soil. Therefore, to obtain measurements of water potential in the dry range, it is necessary to complement the use of HYPROP with the WP4-C [21].  
The HYPROP-FIT software was selected for curve fitting due to its high accuracy and versatility in fitting retention data using various methods. It is particularly effective in fitting both traditional and bimodal (tropical soils) retention curves, accurately capturing the bimodality of the measured retention curves and effectively describing the hydraulic behavior across the entire measurement range [22; 23].  
[PERSON] and [PERSON] [24] claimed that the nature of the fine fraction plays an important role in determining the soil's resilience behavior, and this was taken into consideration. The HYPROP equipment has an optimal measurement range limited to tension values ranging from 0 cm to 1000 cm of the water column. Thus, additional data points were necessary throughout the tests performed using the WP4-C equipment to obtain a more precise delineation of the retention curve obtained with the HYPROP, since the optimal measurement range of the equipment WP4-C varies from 1000 cm to 1,000,000 cm of the water column.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**Characterization**} \\ \hline  & \multicolumn{3}{c}{**Compactation/Intermediate Energy**} & \multicolumn{6}{c}{**Attereberg Limits**} \\ \hline
**Sample** & **MCT** & **USCS** & **W Optimum (\%)** & **MEAS (g/cm\({}^{3}\))** & **DR** & **WI (\%)** & **Wp (\%)** & **PI (\%)** \\ \hline
1 & LA & SP-SM & 6.00 & 2.07 & 2.65 & 17.99 & NP & 17.00 \\
2 & NS\({}^{\prime}\) & CL & 15.40 & 1.67 & 2.72 & 35.00 & 0 & 35.00 \\
3 & LG\({}^{\prime}\) & CL & 6.00 & 1.92 & 2.62 & 29.00 & 19.00 & 9 \\
4 & NA\({}^{\prime}\) & CL & 16.50 & 1.74 & 2.66 & NL & NP & NP \\
5 & NG\({}^{\prime}\) & SC & 16.00 & 1.76 & 2.64 & 27.00 & 10.00 & 17.00 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Characterization of soils from EFC.  
The unsaturated hydraulic conductivity of soil is related to its saturated hydraulic conductivity value as well as its water retention behavior, according to [PERSON] [25]. The determination of the permeability coefficient k involves various methods, which can range from simple calculations to more intricate laboratory and field tests. The selection of the appropriate method for evaluating parameter k primarily depends on the soil type. Eurocode 7 identifies four methods for assessing parameter k, that are crucial to conducting a comprehensive analysis of the soil's properties: laboratory tests, field tests, estimation based on oedometer tests, and empirical correlations [26]. In the present work, the permeability was obtained through laboratory testing using the HYPROP.  
The tests with HYPROP were carried out at the Geotechnical Laboratory of COPPE/UFRJ--Environmental Geotechnics Section and the tests with WP4-C were carried out at Embrapa Solos at Rio de Janeiro-RJ.