Modelling the influence of tree removal on embankment slope hydrology

Trees cover the slopes of many railway earthworks supporting the UK’s transport network. Root water uptake by trees can cause seasonal shrinkage and swelling of the embankment soil, affecting the line and level of the railway track. This requires continual maintenance to maintain the serviceability of the track and reduce train speed restrictions. However, the removal of trees from railway embankment slopes and the loss of soil suctions generated by root water uptake may negatively impact embankment stability, particularly during periods of wet weather. An improved understanding of the influence of tree removal on embankment hydrology is required so that infrastructure owners can develop a managed system of vegetation clearance.

Hydrological field monitoring data from an instrumented railway embankment are presented and compared with a finite element model of root water uptake incorporating daily weather data. It is shown that trees maintain persistent suctions within their root zone which are unaffected by seasonal wetting and drying at the soil surface. However, the removal of trees from the embankment slope causes wetting of the soil from the soil surface as persistent soil suctions within the root zone are lost.