Rebuild a dam with a big crack in it and on the point of collapsing
Carsington Dam is at Carsington Water – a reservoir run by Severn Trent Water in Derbyshire. The reservoir is the 9th biggest in England. It can hold 35,412 megalitres.
The reservoir takes water from the river Derwent at the village of Ambergate during the winter then pumps it through 6.5 miles (10.km) of tunnel and aqueduct. Water is released back into the river during the summer months
Planning for the reservoir started in the 1960s with construction of the 35m-high dam starting in 1979.
In the early hours of 4 June 1984, following a period of heavy rainfall and shortly before the reservoir was due to open, a 50mm crack appeared that ran 120m along the crest of the dam.
The following night there was a major landslip upstream. Around 500m of embankment was affected with soil and earth slipping as far as 11m.
The landslip also left a 15m deep x 30m wide chasm along the crest of the dam.
It was one of the largest geotechnical failures of a structure in the UK. After a lengthy investigation the dam was largely rebuilt.
The reservoir was finally opened by the Queen in 1992.
"The failure was sudden and catastrophic.”THE NEW CIVIL ENGINEER November 1998
Carsington dam reconstruction
Ian Hope talks to us about the challenges he is confronted with in his role as Dams and Reservoirs Manager for Severn Trent Water and the history of Carsington Dam, first built in 1984 and reconstructed in 1992.
Did you know …
Sir Alec Skempton was one of the founding fathers of soil mechanics , a branch of engineering that describes the movement of earth.
His forensic analysis of the 1937 collapse during construction of the Chingford reservoir is regarded by many as the birth of soil analysis in the UK.
Skempton was also a founding member of ICE’s Soil Mechanics and Foundations committee – now the British Geotechnical Association.
Difference the dam reconstruction has made
Carsington reservoir provides water to over 3 million people across Derbyshire, Nottinghamshire and Leicestershire.
It holds enough to fill 2 other Peak District reservoirs: the Ladybower and Upper Derwent.
Without the 1992 dam reconstruction owners Severn Water would have difficulties supplying their customers with enough water.
Additionally, the reservoir’s position is viewed as ideal because the surrounding hills produce a ready supply of rainwater.
This reduces the need to store water, cutting down environmental impact on the surrounding landscape.
How the work was done
The reservoir owners asked a project team headed up by soil mechanics expert Sir Alec Skempton to investigate the dam’s failure and advise on its repair or replacement.
The team took 1,260 soil samples and carried out a wide range of tests on the dam. These included stress-testing the dam structure as well as measuring movement in the earthworks with sensitive instruments.
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.
Following the team’s investigations engineers removed the original embankment over the entire length of the 1984 landslide.
They then used the excavated soil to buttress (reinforce) the part of the embankment that had not failed. They also used some of the soil to strengthen bank foundations further upstream.
There was one major change in layout – the public road, originally running along the crest of the dam was moved to land running by the reservoir downstream. This was to give the road better protection against winter weather.
The investigation and rebuilding project took 8 years to complete.