Monotonie and cyclic behaviour of root-reinforced sand

Plant roots are known to provide mechanical reinforcement to soils upon shearing and seismic loading. However, the effects of different stress paths on root reinforcement remain unclear. Moreover, whether and how roots provide resistance to soil liquefaction upon cyclic loading have rarely been studied. The objective of this study is to conduct a series of undrained triaxial tests to investigate the monotonic and cyclic behaviour of rooted sand. Roots of vetiver grass (Chrysopogon zizanioides L.), which has been advocated for use in shallow slope stabilisation purposes, were used for testing. The root diameters ranged between 0.3 and 1.5 mm, while the root volume ratios (RVRs) were 0.23%, 0.45%, and 0.67%. It was discovered that the root reinforcement effect was anisotropic and path-dependent. Along the extension path, when the major principal stress was perpendicular to the predominant root orientation, the root-induced increase in soil friction angle was approximately 10[degrees]. This increase was much greater than that along the compression path, where the change was minimal. The presence of roots prevented the limited flow failure at some RVRs and cyclic stress ratios (CSRs) (which occurred in the unreinforced sand) and the failure mode of the root-reinforced soil switched to cyclic mobility. The liquefaction resistance was improved with an increase in root volume, and this improvement was more remarkable at higher CSRs. Key words: vegetation, root reinforcement, soil-root interaction, stress paths, liquefaction. Les racines des plantes sont connues pour apporter un renforcement mecanique aux sols en cas de cisaillement et de charge sismique. Cependant, les effets des differentes voies de stress sur le renforcement des racines ne sont pas clairs. En outre, on a rarement etudie si, et comment, les racines offrent une resistance a la liquefaction du sol en cas de charge cyclique. L'objectif de cette etude est de mener une serie de tests triaxiaux non draines pour etudier le comportement monotone et cyclique du sable enracine. Des racines de vetiver (Chrysopogon zizanioides L.), dont l'utilisation a ete preconisee pour la stabilisation des pentes peu profondes, ont ete utilisees pour des essais. Le diametre des racines variait entre 0,3 et 1,5 mm, tandis que les rapports de volume des racines (RVR) etaient de 0,23 %, 0,45 % et 0,67 %. On a decouvert que l'effet de renforcement des racines etait anisotrope et dependant de la voie. Le long du trajet d'extension, lorsque la contrainte principale majeure etait perpendiculaire a l'orientation predominante des racines, l'augmentation de l'angle de frottement du sol induite par les racines etait d'environ 10[degrees]. Cette augmentation a ete beaucoup plus importante que dans le cas du chemin de compression oU le changement a ete minime. La presence de racines a empeche la defaillance de l'ecoulement limite a certaines RVR et taux de stress cyclique (CSR) (qui s'est produite dans le sable non renforce), et le mode de defaillance du sol renforce par les racines est passe a la mobilite cyclique. La resistance a la liquefaction a ete amelioree par une augmentation du volume des racines, et cette amelioration a ete plus remarquable a des CSR plus eleves. [Traduit par la Redaction] Mots-cles : vegetation, renforcement des racines, interaction sol-racine, parcours de stress, liquefaction.
Introduction Soil bioengineering using vegetation is considered an environmentally and ecologically friendly bioremediation technique for resisting shallow soil slope failure resulting from excessive rainfall (Stokes et al. 2014; Ni et [...]