## 1 Introduction
These curves can be modeled using various hydraulic models. This study used the van Genuchten hydraulic model [31; 32; 33], available in Plaxis 2D. Proper parameterization of these elements enables a more realistic and detailed analysis of how rainfall infiltration affects slope stability [34]. Two soil types were selected for modeling the slope: poorly graded sand with 6.5% fines, classified as SP-SM [32], and well-graded sand with 11.9% fines, classified as SW-SM [33]. The choice of these materials is based on their differentiated behavior in terms of permeability, compaction, and stability under rainfall conditions. Poorly graded sand (SP-SM), with a low proportion of fines, exhibits high permeability and reduced cohesion, making it potentially more vulnerable to infiltration and slope instability [32; 33]. In contrast, well-graded sand (SW-SM), with higher fine content, shows better apparent cohesion, reducing permeability and increasing erosion resistance [32; 33]. This selection enables a comparative evaluation of the effect of gradation properties and fine content on slope stability under rainfall conditions. This study aims to investigate the effect of rainfall on the stability of unsaturated soil slopes, specifically under high-intensity rainfall with varying durations, to obtain the safety factor (S.F.) as a comparative value for each proposed case. The safety factor analysis was conducted using the \"Strength Reduction Factor\" (SRF) method [35], available in Plaxis 2D. This method progressively reduces soil strength parameters, such as cohesion and friction angle, until failure occurs. The findings of this study highlight that SW-SM soil, due to its higher fines content and water retention capacity, experiences a significant reduction in its safety factor under prolonged rainfall, making it more susceptible to instability [36]. In contrast, SP-SM soil, with lower fines content and higher permeability, shows less sensitivity to infiltration, maintaining a relatively constant safety factor. These results emphasize the critical impact of soil hydro-mechanical properties on slope stability under intense rainfall conditions [15]. This study is limited by the simplification of real-world conditions, as it models specific scenarios of intense rainfall (30 mm/h) on two soil types without accounting for external factors such as seismic activity or vegetation. It is well known that vegetation has a significant impact on infiltration capacity [37; 38], but this is beyond the scope of the present research. Additionally, the results depend on the parameters assumed in Plaxis 2D, which could limit their applicability to more complex contexts. Rainfall intensity is a determining factor in slope stability, especially in areas prone to heavy precipitation. This study modeled a slope with a 45\({}^{\circ}\) inclination for two soil types under the influence of rainfall with an intensity of 30 mm/h. Different scenarios with rainfall durations of 24, 18, 12, and 8 h were analyzed to evaluate their impact on slope stability. These results provide insight into how the combination of slope angle, soil type, and rainfall duration affects the safety factor of slopes.