Influence of roots on the hydro-mechanical performance of a drainage geocomposite

Geosynthetics are increasingly used in geotechnical works in association with vegetation, whose function has been typically considered as an improvement for the works themselves, especially due to the mechanical and hydraulic effects the root system provides. Within this context, the paper presents an experimental study performed to evaluate the long-term performance of geosynthetics, specifically drainage geocomposites, exposed to the influence of roots. Two species of plant were selected for their fast-growing and pervasive roots, Vetiver and Bamboo, and planted in a thin layer of growing medium, which buried the geosynthetic specimens. After a period of plant growth, the specimens affected by roots ("rooted specimens") were exhumed, and submitted to tensile and drainage capacity laboratory tests, to determine their mechanical and hydraulic behaviour. The laboratory test results were compared with those obtained on virgin specimens of drainage geocomposite, under undisturbed conditions ("reference specimens"). The results show a decrease in drainage capacity for rooted specimens, more pronounced in the case of the highest density of roots into the drainage core. Concerning the tensile behaviour, no significant variations emerged in rooted specimens, although a slight increase in tensile strength, together with a modest decrease in elongation at maximum load, could be observed.