Erosion | Dispersive behaviour
Internal erosion in clayey soils is associated with dispersion which can be a major contributing factor in the failure of earth embankment dams. As a recent British Dams Society seminar highlights, for dams constructed without filters and of poor construction, it is critical to understand the nature of dispersive soils so they can be treated, or so appropriate remedial measures applied
Below: The Pennines
THERE ARE AROUND 2500 large, raised reservoirs in the UK and according to data from 1975-2000, there has been an estimated 1600 dam incidents recorded for every failure during this period. Sixty percent of these are associated with seepage-induced internal erosion of soil. Two serious erosion incidents also occurred each year. The problem, as Elisabeth Bowman, a reader in geomechanics from the University of Sheffield, explains, is when you do an assessment of a dam with some kind of seepage distress that could be manifested as excessive seepage or settlement, it’s often inconclusive as to what the current cause is. And one of the issues is that UK embankment dams
tend to be more clay dominated and/or of more mixed soils (sand, gravel, clay and silt). Whereas most dams globally tend to be more granular dominated so that the rules of internal erosion are a bit more cut and dried.
If looking at internal erosion in general, it manifests
more evidently in non-plastic or granular soils as different types of internal erosion such as suffusion, backward erosion, contact erosion, and concentrated leak erosion. These have all been well documented and can lead to excessive leakage and sink holes etc, depending on grain size, distribution of the soil, hydraulic load, and total stresses applied. Dispersion on the other hand, tends to manifest
14 | November 2025 |
www.waterpowermagazine.com
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