A novel root system for simulating transpiration-induced soil suction in centrifuge

Plant transpiration has potential beneficial effects to slope stability because it increases soil suction, which results in not only an increase in shear strength but also a decrease in water permeability. Although the effects of vegetation on slope stability have been recently investigated using centrifuge, contributions of plant-induced suction are ignored. In order to simulate transpiration-induced suction in a centrifuge model test, a novel root system that enables suction to be induced and controlled at high-g are developed and verified in this study. This new root system consists of a high air-entry value (AEV) porous filter, cellulose acetate, which has scaled mechanical properties, including tensile strength, elastic modulus, and axial rigidity, similar to living roots. This filter is fully saturated with de-aired water and it is connected to an airtight chamber for controlling vacuum pressures. The function of the water-saturated porous filter is to maintain hydraulic gradient between soil and the root system for any vacuum pressure lower than the AEV of the filter. Any reduction of soil moisture due to applied vacuum hence induces suction. Suctions induced by the new root system were verified to be consistent with those induced by a living tree (Schefflera heptaphylla) at 1-g and that retained by vegetation in the field. Both vertical and horizontal influence zones of suction of the living tree were captured. For centrifuge tests carried out at 15-g, suctions of up to 25 kPa can be simulated.