Effect of climate on internal erosion in embankment dams and flood defences

Internal erosion occurs where soils are eroded from within geotechnical structures such as embankment dams and levees by water seepage. It is one of the two most common causes of failure in dams and levees, both worldwide and in the UK. Wetter winters will lead to dramatic increases in peak river flows and the increased risk of summer drought followed by convective storms will increase the occurrence of flash floods, meaning that dams and levees will be subject to greater hydraulic loads. The soil from which they are constructed will also be subject to greater wetting and drying cycles related to increased evaporation and rainfall. The effect of this cycling on soil erosion resistance is unknown. This research will be the first to study how such climate processes affect internal erosion. The results will be placed within an unsaturated soil mechanics framework to allow a deep understanding of the effect of climate change, and the specific mechanisms which drive these effects. The data will be used to create a science-based predictive model about how these soils may deteriorate when subjected to climatic cycles.

The hypotheses for experimental investigation is:

- Climate induced wetting and drying cycles will cause deterioration leading to a reduction in the erosion resistance of embankment fill materials. The affected infrastructure will include UK embankment dams and levees. Such cycles have always occurred but their severity is likely to increase due to climate change.

The specific Objectives for the project are:

1) Construct and commission a state of the art hole erosion testing device (HET). The HET is an experimental technique to determine the erosion resistance of embankment soils and is the most widely used research tool for this purpose. Results of tests on model soils will be benchmarked against other groups' published results.

2) Subject fills to wetting and drying paths to mimic those in real embankments. Both real embankment fills and laboratory soils with similar characteristics to susceptible materials from UK dams will be tested. The method should be repeatable and create samples which are homogeneous in terms of density and water content.

3) Carry out a series of HET tests to obtain high quality data describing the erosion resistance of soils which are: (i) as compacted and (ii) subjected to wetting / drying paths following compaction.

4) Create a predictive model of how the erosion resistance of embankment materials is likely to change over their lifetime. This will link measurable soil properties to the change in erosion resistance from the as-compacted state.