The performance of embankment dams with filters coarser than ‘no-erosion’ design criteria

This paper summarizes case histories of 28 embankment dams which have experienced internal erosion and piping incidents. All the dams have filters or transition zones downstream of the core which were coarser than required by modern no-erosion design criteria, but the filters appear to have eventually sealed (arrested erosion) despite experiencing significant leakage flows. The performance of the dams is shown to relate to whether the filter or transition zone falls into the ‘some erosion’, ‘excessive erosion’ or ‘continuing erosion’ category. This includes leakage rates. These results can be used to assess existing dams which have filters or transitions which are coarser than no-erosion filters, and to assess the probability of the dam being able to experience the likely leakage without failing by slope instability or unravelling of the downstream slope, before the filter starts to seal.