The collapse of Chingford reservoir, in Essex on 19 July 1937 was undoubtedly one of the most important events in the development of British geotechnics.
The partial failure of part of the embankment dam around Chingford reservoir No2 not only brought the 'father of soil mechanics' Karl Terzaghi to the UK, but also thrust the subject into the public eye and prompted the contractor John Mowlem to set up the country's first commercial soils laboratory.
At first, it was not clear why the 5.7km long earth embankment failed when it was 8m high, 2.5m below crest level. The older King George V reservoir dam nearby had been built in a similar way on similar ground - soft clay overlying sandy gravel overlying London Clay - without incident. The older dam had been built over a period of three years which had allowed pore pressure to dissipate, the clay to consolidate and gain strength, in what was in effect staged construction. In contrast, the newer dam was built more quickly and so failed.
The project is thought to be the first time movements at a slip surface were monitored scientifically. Six inch nails were inserted above and below the flat lying slip surface and their relative movement measured by Skempton using a two foot rule.