Where: ψ = suction (kPa) AEV = suction at air entry, kPa θ = water content θ10 = water content at suction equal to10 kPa θs = saturation water content (%S) = percentage of sand (%C) = percentage of clay and the remaining parameters (a–v) are constant coefficients (Saxton et al. [34]; Shahnazari et al. [21])