A critical evaluation of predictive models for rooted soil strength with application to predicting the seismic deformation of rooted slopes

Abstract

This paper presents a comparative study of three different classes of model for estimating the reinforcing effect of plant roots in soil, namely (i) fibre pull-out model, (ii) fibre break models (including Wu and Waldron's Model (WWM) and the Fibre Bundle Model (FBM)) and (iii) beam bending or p-y models (specifically Beam on a Non-linear Winkler-Foundation (BNWF) models). Firstly, the prediction model of root reinforcement based on pull-out being the dominant mechanism for different potential slip plane depths was proposed. The resulting root reinforcement calculated were then compared with those derived from the other two types of models. The estimated rooted soil strength distributions were then incorporated within a fully dynamic, plane-strain continuum finite element model to assess the consequences of the selection of rooted soil strength model on the global seismic stability of a vegetated slope (assessed via accumulated slip during earthquake shaking). For the particular case considered in this paper (no roots were observed to have broken after shearing), root cohesion predicted by the pull-out model is much closer to that the BNWF model, but is largely over-predicted by the family of fibre break models. In terms of the effects on the stability of vegetated slopes, there exists a threshold value beyond which the position of the critical slip plane would bypass the rooted zones, rather than passing through them. Further increase of root cohesion beyond this value has minimal effect on the global slope behaviour. This implies that significantly over-predicted root cohesion from fibre break models when used to model roots with non-negligible bending stiffness may still provide a reasonable prediction of overall behaviour, so long as the critical failure mechanism is already bypassing the root-reinforced zones.

Small-scale modelling of root-soil interaction of trees under lateral loads

“…Most of the existing literature in soil bioengineering (e.g. Mickovski et al 2010;Liang et al 2019) has demonstrated that the lateral earth pressure coefficient, K, of the soil in the vicinity of the roots being axially uprooted was higher than K 0 (coefficient at rest) but lower than K p , which is consistent with the theory of cavity expansion. However, due to the complexity of the root models being investigated in this study, it was difficult (if not impossible) to precisely determine the values of K mobilised at different positions within the root system.…”

Agar with embedded channels to study root growth

“…Pull-out force of plants from soils has been widely used to study the effect of plant roots on soil stability 27,28 . Pull-out force of plants depends on many factors including root architectural features such as tap root length and branching points as well as root mechanics such as tensile strength and elastic modulus.…”

How Do Roots Interact with Layered Soils?

“…Image segmentation and deep learning allows the quantification of the soil mechanics parameter (i.e., the void ratio), and the root property (i.e., the root volume ratio). The importance of these parameters is evident in constitutive modelling [18][19][20][21], where these parameters contribute to the calculation of the soil strength, or quantifying the root reinforcement. These models allow the behaviour of soil to be predicted to assess the stability of slopes.…”