Mohammad Hadi Khabbaz

Numerical and Experimental Study of Tree Influence on the Ground

A mathematical model for the rate of root water uptake has been developed considering ground conditions, type of vegetation and climatic parameters. The three independent features in the root water uptake model incorporated in detail are soil suction, root distribution, and potential transpiration. A two dimensional finite element approach has been employed to solve the transient coupled flow and deformation equations in vicinity of a tree. To validate the model, an array of field measurements and the data have been compared with the numerical predictions. The predicted results acquired from the numerical analysis have been compared favourably with the field and the associated laboratory measurements, justifying the assumptions upon which the model has been developed.

ANALYSING SOFT GROUND IMPROVEMENT CAUSED BY TREE ROOT SUCTION

Bioengineering aspects of native vegetation are currently being evolved to improve soil stiffness, slope stabilisation, and erosion control. Vegetation contributes to weak soil stabilisation through reinforcement of the soil, dissipation of excess pore pressures, and increasing the shear strength by induced matric suction. This paper looks at the way that vegetation influences soil matric suction, shrinkage, and ground settlement. A theoretical model previously developed by the authors for the rate of tree root water uptake together with an associated numerical simulation is used in this study. A conical shape is considered to represent the geometry of the tree root zone. Based on this proposed model, the distribution of moisture and the matric suction profile adjacent to the tree are numerically analysed. Field measurements taken from previously published literature are compared with numerical predictions for further validation. The predicted results compared favourably with the measured results, justifying the assumptions upon which the model was developed. It is desirable to consider the influence zone of tree roots and the improved soil properties in modern geotechnical designs, benefiting from native vegetation.

Parametric study on suction effects induced by tree roots on ground conditions

A model developed for the rate of tree root water uptake is applied numerically based on finite element analysis, to investigate the effects of the soil, tree and atmospheric parameters on the ground behaviour. The influences of potential transpiration rate, permeability coefficient, and the maximum root length density are studied and quantified. Although the rate of transpiration increases the soil matric suction and the ground settlement, permeability (saturated) decreases the matric suction generated and the corresponding settlement. The maximum root density also affects the change in peak matric suction as demonstrated in the paper.