Using vegetation in geotechnical engineering

Vegetation is often found near infrastructure, including on natural and man-made slopes and alongside transport corridors.

Plant roots offer potential benefits for use as a low-cost, carbon-neutral natural alternative to conventional ground reinforcement techniques. However, they are rarely incorporated explicitly within geotechnical design, principally due to perceived issues of unpredictability in location and variability in biomechanical root properties.

Though earthquakes are rare in the UK, the use of vegetation to improve the seismic performance of slopes will initially be considered. It will be shown how the study of this specific problem is particularly useful when physical modelling is to be undertaken.

Centrifuge testing, combined with a novel use of 3-D printing to produce repeatable and highly representative scale model root analogues, will establish that plant roots can be just as effective in improving slope stability as conventional methods of reinforcement.

Having demonstrated the benefits of vegetation, it will further be shown how the mechanical reinforcement from roots observed in the centrifuge may be incorporated into routine Limit Analysis (LA) or Finite Element (FE) simulations. Such analyses demonstrate a fundamentally different mechanism by which roots improve stability, with knowledge of root spread and depth being at least as important as outright biomechanical root strength. Novel approaches for determining these input parameters using recently developed rapid in-situ testing techniques will be introduced.

The final part of the lecture will explore how this new insight and modelling approach may be applied to a wider range of practical problems including:

• extending the design life of slopes in seismic areas and under the effects of climate change;
• the effect of tree removal on stability of railway embankments;
• use of vegetation in debris-flow protection systems;
• understanding windthrow hazard from storms.

Through the evidence provided and the tools developed, use of vegetation can become a realistic eco-friendly technique for use in practical Geotechnical Engineering.