Abberton Reservoir

Following the forecast of a substantial growth in future demand for public water supply in the east of England, an upgrade to the existing Abberton main dam was planned to raise the water level within the reservoir by 3.2m in order to boost system yield and improve security of water supply. Following a series of studies looking at various options, it was decided to raise the dam by placing the ‘new’ fill material above the existing downstream shoulder and continuing the present upstream slope up to the new crest level. The existing 15.5m high main embankment was completed in August 1938, but the upstream embankment shoulder of the ‘original’ dam suffered deep-seated failure through its foundation towards the end of construction in July 1937. The dam was subsequently rebuilt successfully, and it has performed in a satisfactory manner ever since.

GCG was commissioned to carry out advanced finite element (FE) analyses of the Abberton main dam and its planned raising. The main purpose of the analyses was to confirm the adequacy of the design proposals for the dam raising, primarily regarding the dam’s stability during construction and subsequent operation. In order to check the stability of the raised dam, it was decided to model the complete history of the existing dam. The model parameters were initially derived on the basis of the available site investigations. The failure of the ‘original’ dam and the post-construction behaviour of the existing dam served to calibrate the constitutive models (and their parameters) chosen for the characterisation of the various materials involved. The FE analyses successfully predicted the upstream slope failure towards the end of construction of the ‘original’ dam. They predicted the observed satisfactory behaviour of the re-constructed dam. The modelling of the dam raising closely following various planned activities showed the adequate embankment stability during all phases of work. The analyses were also used for the design of dam instrumentation, and provided the settlement, horizontal displacement and pore water pressure profiles at the various inclinometer and piezometer locations for performance evaluation during the main dam raising.

References

Kovacevic, N., Hight, D. W., Potts, D. M. & Carter, I. C. (2013). Finite element analysis of main dam at Abberton, Essex. Geotechnique, 63(9), 753-767