A Specialized Boundary Condition for Soil–Vegetation–Atmosphere Interaction in Embankments

Plants impact the liquid balance at the root zone and subsequently influence soil suction. Because geotechnical models often neglect the influence of vegetation on the surface of embankments, this paper developed a specialized boundary condition that captures interactions among atmosphere, vegetation, and soil. A boundary is incorporated in a finite-element code called Code_Bright, designed for solving the energy and water balance equations in porous media. In this code, the resistance of the canopy is improved by defining connections with vapor pressure fraction, solar radiation, and volumetric water content. Furthermore, the drying and wetting cycles caused by the atmospheric loads are simulated using a hysteretic soil water retention approach. To validate the model predictions, soil temperature, water content, and liquid pressure measurements were collected from an extensively instrumented slope in Barcelona, Spain, monitored under meteorological data for nearly 3 years. This vegetated slope included two instrumented sections with different orientations: one on the south, and the other on the north. The agreement between field data and simulation results confirmed the model’s robustness and reliability. The saturation degree derived from the hysteretic model demonstrated trends that align more closely with instrument measurements than do those of nonhysteretic models. For both the model and the measurements, the temperature fluctuation is strong at superficial depths, about half of the root zone, but less significant at deeper levels. Additionally, due to differences in the angles of solar radiation on the south and north sides, the temperature predicted by the model was higher on the southern section than on the northern part, which is consistent with the measurements.