Modelling of unsaturated ground behaviour influenced by vegetation transpiration

Abstract

Vegetation contributes to weak soil stabilisation through reinforcement of the soil, dissipation of excess pore pressure and increasing the shear strength by induced matric suction. This paper describes the way vegetation influences soil matric suction, shrinkage and ground settlement in the vadose zone through transpiration. A mathematical model for the rate of root water uptake, including the root growth rate considering ground conditions, type of vegetation and climatic parameters, has been developed. A finite element approach is employed to solve the transient coupled flow-deformation equations. The finite element mesh is built using partially saturated soil elements capable of representing the salient aspects of unsaturated permeability and the soil water characteristic curve. The model formulation is based on the effective stress theory of unsaturated soils. Based on this proposed model, the distribution of the ground matric suction profile adjacent to the tree is numerically analysed. Current field measurements of soil matric suction and moisture content collected from Miram site located in Victoria State, Australia by the authors are compared with the numerical predictions. The results indicate that the proposed root water uptake model incorporated in the numerical analysis can be used for prediction of ground properties influenced by tree roots.

Keywords:

• root water uptake
• root density distribution
• unsaturated soil
• native vegetation
• finite element modelling
• soil suction

Acknowledgements

The contributions and feedback from various industry colleagues, particularly Wayne Potter and David Christie, are appreciated. The assistance of Dr Don Cameron of University of South Australia is also acknowledged.

Funding

This research has been sponsored by the Australian Cooperative Research Centre for Railway Engineering and Technologies (Rail-CRC).