Preliminary modelling of the saturation of a full-sized clay and concrete shaft seal

Abstract

AbstractA shaft seal was installed at the intersection of the 5 m-diameter access shaft of the Atomic Energy of Canada Limited's Underground Research Laboratory with a major, moderately dipping fracture zone (FZ) to limit the mixing of the saline groundwater at the zone below the FZ with freshwater at the zone above the FZ. The shaft seal consists of 6 m-thick clay-based material that is sandwiched between 3 m-thick upper and lower concrete components, and its centre is located at c. 273 m depth below the surface. This paper presents the results of preliminary finite element analyses using 2D-axisymetric and 3D geometries simulating the saturation of the shaft seal. The components in the analyses include the clay, concrete, intact rock and FZ. Of particular interest are the field-observed differences in the hydraulic pressures above and below the shaft seal. The results of the numerical analyses were compared with the 3-year monitoring data. The results of the numerical models showed that the decrease in the pressure difference indicates that there was flow path that connects the zones above and below the shaft seal. A preliminary long-term estimation of the shaft seal hydraulic response (up to 1000 years) was done based on the hydraulic pressure and excavation volume data, combined with the assumptions that that the groundwater level will eventually recover to the initial conditions.