Influences of root-induced soil suction and root geometry on slope stability: a centrifuge study

Soil bioengineering using vegetation has been recognised as an environmentally friendly solution for shallow slope stabilisation. Plant transpiration induces suction in the soil, but its effects to slope stability are often ignored. This study investigates the influences of transpiration-induced suction and mechanical reinforcement of different root geometries (i.e., tap- and heart-shaped) to the slope stability subjected to an intense rainfall with an intensity of 70 mm/h (prototype scale; corresponding to a return period of 1000 years), via centrifuge modelling. New model roots that have scaled mechanical properties close to real roots were used to simulate transpiration-induced suction in the centrifuge. Transient seepage analyses were performed using SEEP/W to back-analyse the suction responses due to transpiration and rainfall. Subsequently, the back-analysed suction was used to assess the factor of safety of the slopes using SLOPE/W. It is revealed that heart-shaped roots provided greater stabilisation effects to a 60o clayey sand slope than tap-shaped roots. The heart-shaped roots induced higher suction, leading to 14% reduction of rainfall infiltration and 6% increase in shear strength. Although transpiration-induced suction in a 45o slope was reduced to zero after the rainfall, mechanical root reinforcement was found to be sufficient to maintain the slope stability.