ARTIFICIAL PLANT ROOT SYSTEM
Soil bioengineering using vegetation has been considered an ecologically and environmentally friendly solution for stabilising shallow slopes, alternative to existing traditional engineering methods. Plant roots can generally reinforce the shallow soil through two mechanisms, namely mechanical reinforcement and hydrological effects of plant transpiration. The former relies on the mobilisation of root tensile or/and flexural strength to reduce the shear stress transferred to the soil in the vicinity upon shearing. The latter mechanism induces root-water uptake, which would reduce soil moisture content (or increase in soil suction), hence increasing the soil shear strength and reducing the hydraulic conductivity.
Modelling the mechanical root reinforcement has been attempted in previous centrifuge modelling, yet the modelling of the plant hydrological effect remains a challenge. Researchers in the Geotechnical Centrifuge Facility pioneers the use of an artificial root system that can realistically model both the mechanical and hydrological effects of plant roots of different geometries simultaneously (Fig. 1). The artificial root is made of cellulose acetate which has mechanical strengths highly resemble those of real roots and has a high air-entry value. The latter feature allows a negative water pressure to be maintained when a vacuum pressure is applied to the root. By carefully controlling the magnitude of the vacuum pressure, the amount of matric suction can be flexibly induced and controlled in a model slope. Figure 2 is a typical centrifuge model set up of a compacted soil slope reinforced by an array of artificial tap roots. The model setup also includes a vacuum chamber which allows different amount of vacuum pressure (hence plant-induced suction) to be controlled and also a water reservoir for controlling rainfall (Fig. 3).
Figure 1. Modelling of artificial roots of idealized geometries
Figure 2. A model soil slope reinforced by arrays of artificial tap roots in the centrifuge
Figure 3. Model package for applying vacuum to the artificial roots and water reservoir for applying rainfall
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