The present study investigates the efficacy of a Climate Adaptive Barrier layer (CABL) made of an amended soil (5% by dry mass of waste from a water treatment plant) overlying the natural silty sand by means of numerical modelling. The hydro-mechanical behaviour of the soils was modelled using the Mohr-Coulomb constitutive model, incorporating Bishop’s effective stress, while the van Genuchten model was considered to account for the hydraulic behaviour. A fully coupled flow deformation analysis based on Biot’s theory of consolidation was carried out. After validating the model against the experimental data, a parametric study was conducted to examine the influence of CABL thickness on moisture migration under atmospheric drying. The results indicate that increasing CABL thickness delays the drying front progression. A rapid increase in suction was observed for CABL thicknesses of 50 and 100 mm, followed by a gradual increase for 150 mm, while beyond 150 mm, changes in suction became marginal. The outcome of this study provides guidance on determining the optimal CABL thickness for controlling moisture migration.