The influence of tree root water uptake on the long term hydrology of a clay fill railway embankment

Abstract

This paper uses a numerical model to investigate the influence of tree root water uptake and tree removal on pore water pressures and the vertical movement of a clay fill railway embankment. Simulated results of soil wetting and drying are compared with field measurements from an instrumented railway embankment before and after tree removal. A parametric study compares the influence of vegetation on the seasonal movement of the embankment slope. The simulations and field measurements show that while trees cause significant seasonal variations in pore water pressure and water content near the soil surface, they can maintain persistent soil suctions at depth within the tree rooting zone. Demonstration of this result using a numerical model requires a root water uptake function that separates spatially the processes of water infiltration, evaporation and transpiration. With all of the trees are removed, the persistent soil suctions established by the trees are lost as water infiltrates from the soil surface. Leaving the trees in place over the bottom third of the slope can maintain persistent suctions at the slope toe, while potentially also reducing seasonal ground movements at the crest that may adversely affect railway track geometry.

Measurement of plant xylem water pressure using the high-capacity tensiometer and implications for the modelling of soil–atmosphere interaction

“…Figure 17 also shows the Feddes function based on the parameters commonly adopted in geotechnical applications (diamonds) (u w3 = À100 kPa, u w4 = À1500 kPa (Nyambayo & Potts, 2010;Briggs et al, 2016)). The discrepancy with the experimental data is remarkable.…”

“…The approach proposed by Feddes et al (1978) to model the reduction factor is widely used in geotechnical applications (Hemmati et al, 2010;Nyambayo & Potts, 2010;Greco et al, 2013;Briggs et al, 2016;Tsiampousi et al, 2017;Pagano et al, 2019;Zhu & Zhang, 2019). This approach is convenient because it only requires information about the pore-water pressure in the root zone without the need to address the complex interaction between the soil, the plant, and the atmosphere.…”

Physically based approaches incorporating evaporation for early warning predictions of rainfall-induced landslides

“…Such modelling has been successfully adopted for investigating different issues: e.g. embankment stability analysis (Gitirana Jr., 2005;Briggs et al, 2016), soil-structure interaction (Al Qadad et al, 2012) and generic soil-water budget (Cui et al, 2005).…”

“…Baum et al, 2008;Pagano et al, 2010;Formetta et al, 2016). In other applications evaporation is taken into account by following approaches with different degree of complexity (Casadei et al, 2003;Rosso et al, 2006;Šimunek et al, 2006;Ebel et al, 2010;Formetta et al, 2014;Capparelli and Versace, 2011;Arnone et al, 2011;Endrizzi et al, 2014). Complete approaches, modelling internal and boundary evaporation through hydrothermal approaches, were taken into account in studies referred to slopes in finegrained soils differing substantially from those involved in the case at hand (Cui et al, 2005;An et al, 2017;Song et al, 2016).…”

Climate and Vegetation Impacts on Infrastructure Cuttings and Embankments

“…The Hawkwell site was back analysed by Briggs et al (2016), using the commercial finite element software Vadose/W to try to match the observed changes in soil water content and pore water pressure. Using a set of carefully considered climate, soil water retention, permeability and plant parameters (rooting depth, and root water abstraction with depth), it was found that the model could replicate fairly well the field observed changes.…”