Case Study: Dounreay Shaft Isolation Project
Client: Dounreay Site Restoration Ltd
Location: Dounreay, Scotland
Date: 2006 - 2008
Following the completion of site trials and construction of the Raised Working Platform, the main works to hydraulically isolate the Dounreay shaft were successfully completed. This has resulted in a massive reduction in potential water ingress during future radioactive waste removal operations from an estimated 350m3/day to 12.7m3/day.
The works commenced with site characterisation and baseline hydrological testing followed by bulk infilling of the Liquid Effluent Discharge Tunnel (LEDT) and high pressure rock fissure injection grouting.
All drilling and grouting equipment operated with datalogged sensors and grouting control included realtime ground movement monitoring at depths of up to 100m with a resolution of 0.03mm.
Drilling was undertaken using wireline methods. Custom grout mixes were developed for both LEDT infill and rock fissure injection with ultrafine cements used extensively. BAM Ritchies drilled more than 300 boreholes up to 80 metres deep, with a combined total of 24km.
The work created a nominal ten metre thick barrier around the shaft by grouting fissures in the Caithness Flagstones, reducing rock mass permeability to 5 10-9 m/s. The main grouting works took one year, completing the total project in 2008 after over four years of feasibility studies, investigation, trials, platform construction and shaft isolation.