Text below from EA/DEFRA paper Lessons from Historical Dam Incidents: At the beginning of June 1984, a 400-m length of the upstream shoulder of the embankment dam slipped some 11 m. At the time of the failure, embankment construction was virtually complete with the dam approaching its maximum height of 35 m. Horizontal drainage blankets were incorporated in both the upstream and the downstream shale fill shoulders. The failure surface passed through the boot shaped rolled clay core and a relatively thin layer of surface clay in the foundation of the dam.
From the Institute of Civil Engineers: Analysis showed that the unusual shape of the dam’s clay core had set up a non-uniform distribution of strain through the structure.
The large strains meant the foundation clay – for which there had been very little strength testing – became brittle and failed. This led to the progressive failure of the dam’s upstream side.
At the beginning of June 1984, a 400-m length of the upstream shoulder of the embankment dam slipped some 11 m. At the time of the failure, embankment construction was virtually complete with the dam approaching its maximum height of 35 m. Horizontal drainage blankets were incorporated in both the upstream and the downstream shale fill shoulders. The failure surface passed through the boot shaped rolled clay core and a relatively thin layer of surface clay in the foundation of the dam.
From the Institute of Civil Engineers: Analysis showed that the unusual shape of the dam’s clay core had set up a non-uniform distribution of strain through the structure.
The large strains meant the foundation clay – for which there had been very little strength testing – became brittle and failed. This led to the progressive failure of the dam’s upstream side.