Vegetation for Slope Stability




1 Introduction

Shallow slip failures on embankments and cuttings are iiiore likely in certain geologies, particularly over-

consolidated clays, as identified during the survey of slope condition on motorway earthworks and reported by Perry

( 1989). The reinstatement of these shallow failures can be costly and the potential for slips may be reduced not only

by the use of vegetation planted to provide reinforcement, through the plant root system, but also by a reduction in moisture content and pore water pressure. However, there

is a potential conflict between the engineering reqiiircments of earthwork materials to maintain stability and the moisture requirements to promote and sustain plant growth. For this reason careful selection of plant species is necessary and more information on planting regimes will

reduce any requirement for replacement planting. The use of vegetation and bioengineered approaches also has the advantage of offering improved ecological and aesthetic

benefits, in addition to the improvements in slope stability. In 1995, the Highways Agency (HA) commissioned

TRL to undertake a research project into slope stability and the cstablishment of vegetation. The aim of the project was to review the potential for vegetation as a preventative measure in high risk areas as well as investigating associated aspects such as vegetation reinforced steepened slopes in road widening and the use of live willow poles in

reducing the risk of shallow failures. Bioengineering techniques of this type may reduce the need for the costly maintenance of shallow slip failures on highway

embanlments and cuttings using traditional methods such as those reported by Johnson (1985).


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