Numerical Prediction of Vadose Zone Behaviour Influenced by Vegetation

Bioengineering aspects of native vegetation are currently, and rapidly, being evolved to improve soil stiffness, slope stabilisation, and erosion control. Apart from the reinforcement effect, tree roots establish sufficient matric suction to increase the shear strength and stiffness of the soil. This paper looks at the way, vegetation influences soil matric suction, shrinkage, and ground settlement. A mathematical model for the rate of root water uptake that considers ground conditions, type of vegetation and climatic parameters, has been developed. Based on this proposed model, the distribution of moisture and the matric suction profile adjacent to the tree are numerically analysed. The model formulation is based on the general effective stress theory of unsaturated soils. Field measurements taken from literature published previously are compared with the authors' numerical model. The predicted results calculated using the soil, plant, and atmospheric parameters contained in the numerical model, compared favourably with the measured results, justifying the assumptions upon which the model was developed.