Fig. 4. Relative permeability of undisturbed and disturbed soil samples as a function of water saturation (S_w = /_s). k^f_ra and k^v_ra represent the optimized relative air permeability with tortuosity–connectivity parameter from multistep outflow optimization (l₁) and from fitting to independently measured air permeability data (l₂) using Eq. [5], respectively.