The role of native vegetation in stabilizing formation soil for transport corridors: an Australian experience
This chapter describes a detailed field investigation conducted near an Australian native tree, Eucalyptus largiflorens. This investigation included field procedures such as drilling boreholes and taking soil samples, measuring the soil moisture content, soil suction, and also excavating trenches to observe the distribution of tree roots under the ground. It also includes the development a root water uptake model to examine and explain the soil properties, specifications for vegetation, and meteorological conditions; this root water uptake model incorporates key factors such as soil suction, active root density distribution, and potential transpiration. A two-dimensional finite element approach based on ABAQUS software was used to solve the transient coupled flow and deformation equations. The root water uptake model was implemented into the coupled analysis by introducing a sink term as a subroutine in the finite element analysis. The finite element mesh can be constructed using partially/fully saturated soil elements to represent the salient aspects of unsaturated permeability and the soil water characteristic curve. The model was formulated on the general effective stress theory of unsaturated soils, and based on this proposed model, the matric suction profile adjacent to the tree was analyzed numerically. To verify the model, the soil moisture content and suction profiles measured on site were compared to the predicted values, and profiles of ground settlement and lateral movement adjacent to the tree are presented and interpreted. By considering the various properties of the soil, types of vegetation, and atmospheric conditions, the proposed model would be of most use in predicting how this formation would react in a rail environment because the model developed in this study may improve the design and construction procedures for railway lines, foundations, and embankments near native vegetation. However, because the influence zone of each tree may be several meters in diameter, a methodical planting of native trees along rail corridors at a practical distance away from the rail track is currently being considered by rail organizations. Vegetation, properly selected and used, including native trees and shrubs, can reduce moisture through root water uptake, increase the shear strength and stiffness by increasing the matric suction, and also control erosion.