Hole Erosion Test for UK Soils

The Environment Agency estimates there are over 1.1 million households at risk from the failure of Large Raised Reservoirs (LRRs) and associated dam infrastructure in the UK. The average age of UK dams is approximately 120 years, well over the design life of other forms of civil infrastructure, and the risk of failure is expected to increase with time with age-related deterioration and climate change. A major mode of rapid dam failure is via internal erosion of soil which may occur gradually for years before detection, by which time it may be problematic to mitigate the hazard by drawing down the reservoir to reduce the hydraulic load.

In this project, at the University of Sheffield we are designing and constructing the UK's first Hole Erosion Test (HET) apparatus, suitable for the full range of UK’s soils, to enable quantitative risk assessment against seepage induced erosion within embankment dams and subsequent management to be undertaken. The HET will also enable further fundamental research to be conducted on soils pertinent to UK conditions.

The Hole Erosion Test is considered to provide the best indication of the resistance of a soil against seepage induced internal erosion, via the “Erosion Index” IE. This parameter is fundamental to quantifying the potential time to failure of a widening hole within a dam. Knowing the time to failure allows the breach time to be modelled and hence the potential associated downstream damage and loss of life. With reservoir owners moving towards ALARP risk modelling, this information will be important to ensure any proposed risk reduction measures are proportionate and that owners concentrate efforts where they provide the most benefit.