Climate resilient earthwork design using green infrastructure

There are tens of thousands of miles of vegetated infrastructure slopes, i.e. man-made embankments and cut slopes which support railways and highways, in the UK. Network Rail alone owns 52,000 hectares of land on which there are nearly 6.3 million trees. As earthworks are known to demonstrate poor serviceability when interacting with vegetation, Engineers tend to perceive it as a liability rather than to appreciate it as a national asset.

Well-maintained vegetation, however, has the potential to enhance slope stability and has undeniably positive environmental outcomes. It is estimated that hundreds of millions of pounds will be spent over the next 20-years to manage vegetation while complying with safety and operational standards.

Interaction between atmosphere and soil as an engineering material has only recently attracted significant interest. Serviceability problems arise in densely vegetated slopes during dry periods, as the soil shrinks excessively. Shrinkage is not fully recovered when water from precipitation percolates into the earthworks' soils causing swelling, hence shrinkage accumulates year on year.

This cycle of swelling and shrinkage is expected to intensify, as climate change projections show a substantial increase in rainfall extremes, followed by long periods of intensified drought. On the other hand, vegetation establishment on earthworks can increase slope stability via its roots, reduce the infiltration rate in the soils, protect the soil against erosion.

To properly understand and quantify the problems as well as to propose solutions for best greening strategies, we need to develop robust models integrating water transport from the soils to vegetation and the atmosphere, and soil hydro-mechanical behaviour. Detailed data are needed to validate these models, which upon successful implementation and validation can be used to inform new-generation geotechnical engineering standards for modern construction as well as maintenance of existing earthworks.

The project aims to bridge ecohydrological, soil and geotechnical modelling, with the scope of enhancing the resilience of vegetated infrastructure earthworks to climate change. The project will be organised in the following tasks:

1 Analyse with the aid of the CASE partner Geotechnical Observations field data from selected infrastructure slopes and identify representative case studies;

2 Generate new data though field and laboratory studies (data of soil mechanical and hydraulic properties and field data monitoring the behaviour of existing infrastructure);

3 Develop a unique soil-plant-atmosphere model that integrates geotechnical modelling with all necessary ecohydrological processes. The model development will integrate modelling expertise between the Hydrology and Geotechnics sections at Imperial College London; 4 Perform risk analysis under a changing climate using the last generation CMPI6 climate model projections for the UK.