Modelling the impact of depth distributed plant water uptake on Soil-Plant-Atmosphere Interactions

The soil-plant-atmosphere interaction (SPAI) significantly influences the safety and serviceability of engineering infrastructure by affecting pore water pressure (PWP) distribution. Rainfall and water infiltration increase PWPs, reducing soil strength, while evapotranspiration—driven by evaporation and plant transpiration—induces negative pore pressures (suction), enhancing soil strength and safety. However, vegetation can also pose serviceability challenges. During summer, root water uptake causes soil shrinkage, and in wet months, infiltration induces swelling. These cyclic volume changes can disrupt infrastructure, leading to road and track delays or closures. Accurate modelling of SPAI is therefore critical to understanding the effects of climate change and vegetation on soil hydraulic and mechanical behaviour. This study examines how surface and internal flow boundary conditions affect SPAI modelling within a fully coupled flow-deformation framework. While most recent research has focused on surface boundary conditions for hydrological fluxes, this paper evaluates the inclusion of internal boundary conditions to simulate vegetation transpiration. A comparative analysis assesses the safety and serviceability outcomes for models employing only surface boundary conditions versus those incorporating both surface and internal conditions.