The Enhanced Sealing Project (ESP): 2009–17 monitoring of a full-scale shaft seal installed in granitic rock

Abstract

Abstract The Enhanced Sealing Project (ESP) is monitoring the thermal–hydraulic–mechanical (THM) responses of a full-scale shaft seal at Canadian Nuclear Laboratories (CNL) former Underground Research Laboratory (URL) site. The evolution of such a full-scale construction has direct relevance to closure design of repository shafts (and tunnels) in a range of host rock types. The shaft seal is installed across a water-bearing fracture (fracture zone (FZ2) at c. 270 m depth), marking the interface between deeper, more saline groundwater and nearer-surface freshwater environments. Intended to demonstrate an ability to install a sealing structure that can limit the movement of water between the two hydrological regimes, the main shaft seal consists of a 40% bentonite clay: 60% fine aggregate by dry mass component ( c. 6 m thickness) sandwiched between two 3 m-thick concrete segments in the approximately 5 m-diameter main shaft. The clay and concrete components provide the primary hydraulic sealing and mechanical constraint to the sealing material, respectively. This paper presents the monitoring results of the ESP from its installation in 2009 through to mid-2017. At present, the seal is still not completely water-saturated, pressures within it are still developing and flooding of the upper shaft is continuing. The ESP provides a comprehensive long-term dataset that will assist in calibrating numerical models describing the performance of placement room/shaft/tunnel seals in a Deep Geological Repository.