Engineering geological aspects of the Network Rail earthworks assessment framework

Network Rail has developed a new framework for the assessment of its portfolio of over 190 000 earthworks in Great Britain. Assessment is the qualitative or quantitative determination of the stability or the safe load-carrying capacity of an earthwork. This framework will be summarized in this paper, but the main focus is on the engineering geological aspects that underpin the methodology. Earthworks are mostly constructed in or from natural geological materials, which are highly variable across a network with a large geographical extent. To rationalize the assessment of such a range of materials, a means of grouping them into cohorts of similar engineering behaviour is presented. Then a means of consistently describing the configuration of these materials in a ground model is presented, along with a brief description of how water (as overland flows or groundwater) is considered. The final engineering geological consideration is a new classification system for the potential failure mechanisms that need to be assessed for each earthwork. Finally, the paper describes the interrelationships between the engineering geological considerations that are described in the framework and how these are used to support the application of the new methodology in Network Rail's earthwork asset management procedures.