2023 Géotechnique Lecture

Synopsis

Climate change will affect our aging transportation and flood defence earth infrastructure (embankments, cuttings, slopes adjacent to transport corridors). Infiltrating rainwater/floodwater increases pore-water pressure leading to a reduction in soil shear strength eventually triggering slope instability. Dry/wet periods cause shrink/swell behaviour of clayey geostructures and may contribute towards these geostructures reaching the serviceability limit state.

Ground-atmosphere hydraulic interaction is almost always mediated by a vegetated interface. If adequately ‘engineered’, it can be transformed into a valuable climate change adaptation measure for long linear infrastructure subjected to climatic hazard. Vegetation-based solutions are:

• relatively easy to implement over long distances,
• ‘climate-smart’ due to plant phenotypic plasticity in a changing climate
• carbon neutral/negative.

This lecture will present experimental and numerical evidence showing that transpiration-induced suction (hydrological reinforcement) and lateral drainage promoted by the higher hydraulic conductivity of the root zone (hydraulic reinforcement) can considerably affect the stability of slopes. It is also shown that increasing (e.g., due to vegetation growth) or decreasing transpiration (e.g., due to clearing) can lead to excessive deformations of the clayey geostructure.

These processes occur in the Soil-Plant-Atmosphere Continuum (SPAC) and can possibly be amplified or attenuated via the biotic and abiotic manipulation of the SPAC. This is an approach commonly adopted in agriculture and forest management and the event will discuss the lessons we can learn from plant science to develop geotechnical solutions.

Vegetation and soil microbiota live in a complex evolving ecosystem, and post-intervention field monitoring is required to assess the performance of any nature-based adaptation measure (i.e., the observational method is an intrinsic part of ‘designing with nature’). Field monitoring is also key to characterise the SPAC. We cannot bring large ‘representative’ samples of vegetated interface to the laboratory, instead we need to move our laboratory to the field. The lecture will address the challenges and opportunities in the monitoring of the SPAC.

Finally, the lecture will highlight the problem of designing hydrological reinforcement of slopes via a transpiration model designed to be physically-based in order to guide the choice of suitable plant functional traits.