Effects of plant age on anisotropic saturated hydraulic conductivity of a synthesized rhizosphere using a cubic triaxial permeameter

Understanding the effect of vegetation on anisotropic saturated hydraulic conductivity is essential in the design and performance assessment of bioengineered geostructures. Therefore, this study examines how the age and root biomass of Vetiver grass influence the anisotropic saturated hydraulic conductivity of rhizosphere. Because conventional permeameters cannot reliably measure horizontal and vertical saturated hydraulic conductivity in intact vegetated soils, a recently developed cubic triaxial permeameter was utilized. A total of 76 saturated hydraulic conductivity tests were conducted on specimens cultivated and grown under controlled conditions for 2, 5, and 8 months. The results revealed that increasing plant age and root biomass reduced horizontal saturated hydraulic conductivity by up to 11-fold and vertical saturated hydraulic conductivity by up to two-fold compared with the bare soil, due to root-induced clogging of preferential flow paths. Specifically, the development of dense secondary roots clogs lateral pore spaces, while vertically grown primary roots induce partial preferential flow paths. Although the bare soil exhibits a clear anisotropic behavior ( k h / k v > 3 for void ratio of 0.70), vegetated soils with higher root biomass exhibit almost an isotropic behavior. These findings provide valuable insight for designing and optimizing vegetation-based water management, green landfill covers, and slope stabilization systems.