Vegetative induced ground displacements: a comparison of numerical and experimental study

Abstract

A volume change was modeled as a result of matric suction change caused by vegetative induced moisture transfer. Theory of unsaturated soil mechanics and two stress state variables principles approach was used in the stress-deformation model. The negative pore-water pressures are estimated through governing partial differential equations for unsaturated soils. The results of the root water-uptake analysis are then used as an input for the prediction of ground displacements in a stress-deformation analysis in an uncoupled manner. A mature Leyland Cypress tree located on Gault clay was analyzed, covering a full spring/summer drying period for the first case study. The second and third cases were analysis on Mature Lime tree located on a Boulder clay sub-soil for period covering a full spring/summer drying period; while the third case considered field capacity in winter and extends through a full spring/summer drying period and subsequent autumn recharge. Time varying boundary conditions have also been considered in the third case and the sink term was activated to represent water uptake by transpiration, during spring/summer soil-drying phase and deactivated during the autumn/winter recharge phase. The stress-deformation model has been validated by direct comparison to field measurements recorded for three cases. A good overall correlation between field data and simulated results has been achieved where the difference between the two set of results was less than 5% for all cases considered. Key words: Unsaturated soils, numerical, water-uptake, simulation, stress-deformation, experimental.