Time-dependent deformation behavior of Opalinus Clay at elevated temperatures

For the design of deep geological repositories for radioactive waste it is mandatory to understand the long-term deformation mechanisms under in-situ conditions, including time-dependent rock behavior at elevated temperatures, which are expected in the host rock after waste emplacement. Continuous convergence of tunnels in low permeability clay shales are associated with phenomena such as consolidation (a hydro-mechanical response) and creep (a rheological property). However, they may occur superimposed and targeted laboratory approaches are necessary for an accurate characterization. In the context of radioactive waste repositories, increased temperature may enhance time-dependent processes and affect the long-term safety assessment. In this context, multi-stage creep tests on pre-consolidated specimens were performed in a triaxial setup using sample material from the shaly facies of the Opalinus Clay formation. The tests were conducted on fully saturated specimens under temperature conditions of 30 and 60 °C. First results of our systematic study indicate that elevated temperature (60 °C) may lead to (1) greater strain accumulation during primary consolidation and primary creep phases, and (2) increased secondary creep rates compared to those observed at 30 °C under similar effective stress conditions.