Analytical solutions for calculating pore-water pressure in an infinite unsaturated slope with different root architectures

Abstract

Vegetation can reduce pore water pressure in soil by root water uptake. The reduction of pore water pressure results in higher shear strength but lower water permeability of soil, affecting slope stability and rainfall infiltration, respectively. Effects of different root architectures on root water uptake and hence pore water pressure distributions are not well understood. In this study, new analytical solutions for calculating pore water pressure in an infinite unsaturated vegetated slope are derived for different root architectures, namely the uniform, triangular, exponential and parabolic root architectures. Using the newly developed solutions, four series of analytical parametric analyses are carried out to improve understanding of the factors affecting root water uptake and hence that influence pore water pressure distributions. In the dry season, different root architectures can lead to large variations in pore water pressure distributions. It is found that the exponential root architecture induces the highest negative pore water pressure in the soil, followed by the triangular, uniform and parabolic root architectures. The maximum pore water pressure induced by the parabolic root architecture is about 77% of that induced by the exponential root architecture at the steady state. For a given root architecture, vegetation in completely decomposed granite (CDG, classified as silty sand) induces the highest negative pore water pressure than that in fine sand and silt. The zone influenced by vegetation can be about three to six times the root depth. In wet season, after a ten-year return period rainfall with a duration of 24 hours, different root architectures show similar pore water pressure distributions.

Theoretical analysis of coupled effects of microbe and root architecture on methane oxidation in vegetated landfill covers

“…The total root area for each root architecture is considered to be the same for fair comparison. The distributions of transpiration-induced suction by these four root architectures have been verified by Ng et al (2015a).…”

“…Outside root zone 8 The use of sink term ( ( , ) Sz  ) to capture the process of plant root-water uptake has been verified and frequently used in theoretical models to investigate subsurface water flow for various engineering problems (Feddes et al, 1978;Ng et al, 2015a;Nyambayo and Potts, 2010).…”

“…Plants can develop different root architectures at specific environmental conditions, such as, uniform, triangular, exponential and parabolic shapes ( Fig.1). Experiments (Kamchoom et al, 2014;Ng et al, 2016;Leung et al, 2016) and analytical modelling (Prasad, 1988;Ng et al, 2015a) all shows that transpiration induced by different root architectures could result in significantly different magnitudes and distributions of pore-water pressure and soil water content.…”

“…It is because plants have multiple effects on soil responses which are often coupled and difficult to be isolated from each other. For example, root-water uptake due to different combinations of root architectures and root depths would induce different magnitude and distribution of soil water content (Ng et al, 2015a;Prasad, 1988). Numerical modelling, on the contrary, is a useful means that can systematically investigate the relative importance and significance of each individual factor on MAMO.…”

Trend setting research in “blue” and “green” directions

“…Research on the use of vegetation to improve slope stability has been accelerating. Recent research has focused on mechanical as well as hydraulic effects including soil suction and root architecture (Kamchoom et al, 2014;Ng and Yu, 2014;Ng et al, 2014b;2015f;2015g;Liu et al, 2016). Although some new findings have been made and insights acquired, it is clear that much more research is needed to save the Earth.…”