Sizewell B & C Nuclear Power Stations

Location: Sizewell, UK

Dates: 1989 and 1994-1995

In the late 1980’s proposals for further development of the Sizewell site were in place and a detailed site investigation had been completed. Following completion of this work, designs for a new nuclear power station were prepared which included an excavation to a maximum depth of 12m below ground level. The diaphragm walls were to act as embedded cantilevers and an important consideration in their design was the potential effect of differential movements along their length on the water-tightness of any joints within the wall.

GCG was commissioned to advise on and undertake deformation analyses, appropriate to the design of the proposed diaphragm wall around the site. GCG’s finite element (FE) modelling employed non-linear stiffness characteristics of soils at small strains, which had an important influence on predictions of ground and wall displacements. A number of these analyses were undertaken in order to investigate the impact of various design assumptions on wall movements during the proposed dewatering and the subsequent excavation, and also to assess long-term conditions. The results of these analyses were used to inform the design of potential ground and wall displacements as well as the critical bending moments within the diaphragm walls.

GCG was also employed by Nuclear Electric Ltd (NEL) to give guidance on the ground investigation at Sizewell ‘C’ Nuclear Power Station. This was part of a thorough review of the dynamic properties at a number of their nuclear power station sites by NEL. GCG provided specification on the following activities:

  • Rotary cored sampling of the Norwich Crag and underlying London Tertiaries;
  • Preservation of samples;
  • Laboratory testing for the measurement of small strain stiffness and dynamic properties.

Subsequently, GCG was involved with the interpretation of the laboratory test data and in situ geophysical data to derive parameters for the dynamic analysis that were to be carried out for the Sizewell ‘B’ Nuclear Power Station.