Conceptual Development and Numerical Modelling of Vegetation Induced Suction and implications on Rail Track Stabilisation

The effects of tree roots on soil suction and ground settlement are investigated. This paper highlights the inter-related parameters contributing to the development of a conceptual evapo-transpiration and root water uptake equilibrium model that is then incorporated in a comprehensive numerical model. The developed numerical model based on the finite element analysis (ABAQUS) considers fully coupled flowdeformation behaviour of soil. Field measurements obtained by the authors from a field site in western Victoria and from past literature are used to validate the model. The predicted results show acceptable agreement with the field data in spite of the assumptions made for simplifying the effects of soil heterogeneity and anisotropy. The numerical analysis proves that the proposed root water uptake model can reliably predict the region of maximum matric suction away from the tree axis. The paper also compares the natural favourable effect of tree roots with the stabilising mechanisms of geosynthetic vertical drains subjected to vacuum pressure. Although this analogy is only justified for shallow vertical drains, the comparison still emphasises the obvious economical advantages of native vegetation.

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