## 3 Results
### Numerical Modelling  
The program IVFlow generated a temporal graph of volumetric humidities (t = 0) as an initial step. By analyzing the graph, it was observed that the subballast layer had a moisture content of 22.65 m\({}^{3}\)/m\({}^{3}\) before being subjected to the weather variation. This value was 3.3% below the saturation moisture, and 4.95% higher than the optimum moisture content of the material.  
The elevated initial humidity can be attributed to capillary rise caused by the infiltration of groundwater. This is because in the model construction, a water level of 2.6 m was assigned, and before precipitation, this was the only probable water source for the pavement. After identifying the issue, the simulations were repeated by assigning a higher water level of 10 m. However, the subballast layer continued to exhibit the same initial moisture content.  
The rainfall regime adopted was that of [PERSON], given that the parameters of his equation for the study region were already in the program's database (a:0.156; b:0.08; a:0.4; b:42; c:10). In addition to existing data, the following were also used: start: 0 h; duration: 1 h; ramp-up: 5%; TR: 30 years. The simulation considered a period of three hours of rain.  
Figure 8: Sample 4 retention curve obtained in HYPROP and WPF-C ([PERSON] [14]).  
Figure 7: Sample 4 retention curve obtained in HYPROP ([PERSON] [14]).  
The program's outputs revealed that the subballast layer, composed of sample 1, attained a maximum moisture content exceeding the optimal level by 8.2%. This indicates that rainfall caused a 3.3% increase in the moisture content, considering that the layer already had a moisture content exceeding the optimum by 4.95% prior to the simulation. Furthermore, the results showed that the entire layer underwent a moisture variation greater than 3% compared to the optimal moisture content (see Figures 9 and 10).  
The obtained result confirms the conclusions of previous studies such as [PERSON] [10], [PERSON] [11], [PERSON] [12], and [PERSON] [13], which verified the good performance of fine sandy lateritic soils in railway pavement in terms of mechanical behavior. Specifically, [PERSON] [12], when evaluating the soil from sample 1 in terms of its mechanical behavior, suggests the application of the material as a subballast layer. [PERSON] et al. [2] also verified the good field behavior of the soil classified as LA (laterite sand) in a specific section, which once again confirms the results obtained in this research.  
[PERSON] [12] concluded in her study that LA-type soils are suitable for pavement applications. The author also mentioned that NA-type soils exhibit good mechanical behavior. However, when in contact with water, these soils experience compromised performance, making them suitable for highways that have surface coatings providing protection against moisture. On the other hand, they may not be recommended for railway pavements that lack such protection. These findings align with the hydraulic behavior observed in this study.  
In her research, [PERSON] [13] obtained a bimodal curve for LA soils and a unimodal curve for NA soils, similar to the curves obtained in this study. The hydraulic conductivity value found by the author for saturated LA soil of 0.0758 cm/h is of the same magnitude as the value of 0.009 cm/h found for the LA soil studied in this research. The author also found a value of 0.066 cm/h for NA soil, which is consistent with the value of 0.0074 cm/h found for the same soil type in this study. Both conductivity values are also within the range typically observed for sandy soils.  
Figure 10: Volumetric humidity at the end of the simulation.  
Figure 9: Volumetric humidity at the beginning of the simulation.