Protecting embankments from extreme weather using vegetation

J. Knappet

Embankments are a key element of transport infrastructure that are vulnerable to natural hazards. One such hazard is extreme rainfall, which can lead to excessive deformation or slope failure due to the generation of positive pore water pressures in ground which lower stability. Such events can cause extensive disruption to road and rail links and are likely to become more frequent as a result of Climate Change, an effect which is amplified by an increasing need to extend the design life of existing older embankments due to the high cost of replacement. Plant roots offer potential benefits for use as a low-cost, low carbon, renewable and natural alternative to conventional ground reinforcement techniques, which can help to mitigate Climate Change (via carbon sequestration) while adapting such infrastructure to be more resilient to its effects. However, vegetation is rarely incorporated explicitly within geotechnical design, principally due to perceived issues of unreliability, arising from unpredictability in root location and variability in biomechanical root properties. This presentation will firstly introduce centrifuge modelling as a method for simulating, at small scale, the behaviour of full-scale prototypes of geotechnical infrastructure. This will include the physical modelling of plant root systems at scale using juvenile (live) plants to provide representative amounts of soil reinforcement within the model and the simulation of extreme rainfall events in-flight. Results will then be presented which demonstrate the effectiveness of planting vegetation on compacted embankment slopes, in terms of significantly reducing damaging deformations at the crest during frequent events, and allowing the embankment to safely resist significantly more extreme events. The effects of the vegetation on changing the observed failure mechanics within the ground indicate that perceived uncertainties in root properties are not as important as previously thought. These results are being used to validate new numerical simulation approaches, which along with new in-situ tests for measuring root reinforcement, can enable the adoption of vegetation as an effective and reliable technique for mitigating risk in embankments due to extreme events.