Hydromechanical effects of shaft sinking at the Sellafield site

Under the auspices of the DECOVALEX II project, the coupled hydromechanical responses, in the fractured volcanic rocks at Sellafield site, to a pump test and shaft sinking were studied. The aim of this paper is to describe the methodology for determining the hydromechanical effects of the shaft excavation. This methodology is based on the discrete fracture network (DFN) approach for hydraulic analysis and the discrete approach, where the main discontinuities are explicitly represented in the mechanical model. The principal advantage of using the DFN approach is to easily change the scale of the study without important modifications of the network. Hydraulic properties of the different types of discontinuities were evaluated by calibration of the flow rates induced by a long-term pump test in borehole RCF3 drilled on the centreline of one of the proposed shafts. The same fracture network generated to analyse the RCF3 pump test was used to predict the hydromechanical responses of the rock mass to the excavation of a shaft centred on the RCF3 borehole. This methodology offers some additional possibilities such as studies of the excavation damaged zone (EDZ) and its influence on hydraulic conductivity.