Halcrow supported Edmund Nuttall Limited (now BAM Nuttall Ltd) as subcontract designers on this design and construct target cost contract with UKAEA.
The project was one of several enabling projects being undertaken as part of the Dounreay shaft and silo ILW reclamation programme. This followed earlier Halcrow shaft related projects for UKAEA stretching back to 1995 and two earlier phases of concept development with Edmund Nuttall Limited.
The major components of the project comprised supplementary site investigation, extensive detailed trials and scheme design, followed by construction and validation of a 10m wide, 100m perimeter multi stage grout ring in rock to surround the shaft and extend below its base to a depth of 80m.
The grout ring is required to minimise potential inflows during shaft dewatering, which is to be undertaken as part of the future reclamation of nuclear waste deposited in the shaft in the 1960s and 70s. This is a technologically demanding requirement which entailed the use of advanced grouting technology and hydro-geological mathematical modelling techniques.
The scheme also included shoreline reclamation using roller compacted concrete with an in-situ face to create a suitable working platform, strengthening of the stub tunnel plug that separates the shaft from an adjacent sub-sea low level liquid effluent discharge tunnel and infilling part of the tunnel.
Halcrow worked closely with Edmund Nuttall Limited and its subsidiary Ritchies to provide fully supported and verified designs, specifications, trials programmes and method statements. Halcrow also provided technical support to the site investigations, field trials and the scheme construction. All parties worked closely together to achieve the optimum balance between technical excellence and cost.
The combination of Halcrow expertise in computer modelling, geological interpretation and materials science plus Edmund Nuttall’s expertise in grouting installation enabled a seamless service to the ultimate client UKAEA.