Infiltration rate affects slope stability by determining the rate of water transport to potential failure planes. This note considers the influences of vegetation (grass and willow) establishment and root growth dynamics on infiltration rate, as related to establishing vegetation on bioengineered slopes. Soil columns of silty sand with and without vegetation were tested by constant-head infiltration tests at 2, 4, 6 and 8 weeks after planting. Infiltration rate increased linearly with plant age and below-ground traits including root biomass and root length density. Infiltration rate for willow-rooted soil was an order of magnitude higher than for fallow soil. The plant age effect was more prominent for willow, which grew faster and with thicker roots than the grass. Illustrative seepage analysis suggests that ignoring the plant age effects could underestimate wetting front advancement to greater depths during rainfall, and underestimate suction recovery at shallow depths during internal drainage.

Modelling the seismic performance of rooted slopes from individual root-soil interaction to global slope behaviour T. LIANG Ã , J. A. KNAPPETT Ã and N. DUCKETT † Many natural and man-made slopes are planted with vegetation, and it is known that this can increase the stability of slopes under static conditions. There is anecdotal evidence that vegetated slopes also perform better than fallow slopes during earthquakes. However, the study of the dynamic behaviour of slopes planted with species having dichotomous ('woody') roots is relatively rare owing to the extreme expense and difficulty involved in conducting full-scale dynamic testing on shrubs and trees. In this paper, dynamic centrifuge testing and supporting numerical modelling have been conducted to study this problem. In the centrifuge modelling, ABS plastic rods are used to simulate repeatably the mechanical properties of real roots. The numerical modelling work consisted of two parts. First, a computationally-efficient beam-on-non-linear-Winkler-foundation (BNWF) model using existing p-y formulations from piling engineering was employed to produce a macro-element describing the individual root and soil interaction both pre-and post-failure. By adding contributions from the different root analogues of different diameters, smeared continuum properties were derived that could be included in a fully dynamic, plane-strain continuum, finite-element model in a straightforward way. The BNWF approach was validated against large direct shear tests having stress conditions simulating those in the centrifuge at different potential slip plane depths. The conversion to smeared properties for global time-history analysis of the slope was validated by comparing the continuum finite-element results with the centrifuge test data in terms of both the dynamic response and permanent deformations at the crest, and these demonstrated good agreement. Owing to the simplicity of the BNWF approach and its ability to consider variable root geometries and properties, along with variation of soil properties with depth, it is suggested that the validated approach described will be useful in linking individual root-soil interaction characteristics (root strength and stiffness, diameter variation, root spacing and so on) to global slope behaviour.KEYWORDS: centrifuge modelling; earthquakes; finite-element modelling; numerical modelling; slopes; vegetation INTRODUCTION Vegetation (grasses, shrubs and trees), as an effective and environmentally friendly approach to improving slope stability, improves slope stability mainly through direct mechanical reinforcement of soil and by modifying groundwater conditions by means of evapotranspiration. The net effect of both of these mechanisms is an increase in shear strength within a defined zone around the roots, although only the mechanical effect is present at all times; the hydrological effects potentially disappear following heavy rain. In terms of the direct mechanical effect, many studies have been performed to quantify the increase in soil ...

No abstract

Modelling the seismic performance of rooted slopes from individual root-soil interaction to global slope behaviour T. LIANG Ã , J. A. KNAPPETT Ã and N. DUCKETT † Many natural and man-made slopes are planted with vegetation, and it is known that this can increase the stability of slopes under static conditions. There is anecdotal evidence that vegetated slopes also perform better than fallow slopes during earthquakes. However, the study of the dynamic behaviour of slopes planted with species having dichotomous ('woody') roots is relatively rare owing to the extreme expense and difficulty involved in conducting full-scale dynamic testing on shrubs and trees. In this paper, dynamic centrifuge testing and supporting numerical modelling have been conducted to study this problem. In the centrifuge modelling, ABS plastic rods are used to simulate repeatably the mechanical properties of real roots. The numerical modelling work consisted of two parts. First, a computationally-efficient beam-on-non-linear-Winkler-foundation (BNWF) model using existing p-y formulations from piling engineering was employed to produce a macro-element describing the individual root and soil interaction both pre-and post-failure. By adding contributions from the different root analogues of different diameters, smeared continuum properties were derived that could be included in a fully dynamic, plane-strain continuum, finite-element model in a straightforward way. The BNWF approach was validated against large direct shear tests having stress conditions simulating those in the centrifuge at different potential slip plane depths. The conversion to smeared properties for global time-history analysis of the slope was validated by comparing the continuum finite-element results with the centrifuge test data in terms of both the dynamic response and permanent deformations at the crest, and these demonstrated good agreement. Owing to the simplicity of the BNWF approach and its ability to consider variable root geometries and properties, along with variation of soil properties with depth, it is suggested that the validated approach described will be useful in linking individual root-soil interaction characteristics (root strength and stiffness, diameter variation, root spacing and so on) to global slope behaviour.KEYWORDS: centrifuge modelling; earthquakes; finite-element modelling; numerical modelling; slopes; vegetation INTRODUCTION Vegetation (grasses, shrubs and trees), as an effective and environmentally friendly approach to improving slope stability, improves slope stability mainly through direct mechanical reinforcement of soil and by modifying groundwater conditions by means of evapotranspiration. The net effect of both of these mechanisms is an increase in shear strength within a defined zone around the roots, although only the mechanical effect is present at all times; the hydrological effects potentially disappear following heavy rain. In terms of the direct mechanical effect, many studies have been performed to quantify the increase in soil ...

Small-scale modelling of plant root systems using 3D printing, with applications to investigate the role of vegetation on earthquake-induced landslides.