Frictional Properties of Opalinus Clay
Opalinus Clay (OPA) is the host rock being proposed in Switzerland for disposal of high-level radioactive waste. The stability of fault zones within this formation is a key issue to ensure long-term performance of the repository. To understand the frictional behavior of OPA, we performed velocity steps and slide-hold-slide test on artificial fault gouges and intact samples in the biaxial apparatus BRAVA (INGV, Rome). Microstructures of the sheared material were analyzed after deformation. Results showed peak friction values ranging from 0.33 to 0.52 and steady state friction values ranging from 0.29 to 0.37. We observed a systematically linear decrease of both peak and steady state friction when normal stress increases. Velocity dependence tests on gouge indicates a velocity-strengthening regime, with no points on the unstable region. The friction parameter (a—b) decreases for all test with respect to normal stress, ranging from 0.0072 to 0.0012. Results on intact samples showed both velocity-strengthening and -weakening regimes depending on the up-step velocity and the orientation of the bedding planes. An evolution from negative to positive frictional healing rate is observed for both gouge and intact samples as function of holding times and normal stress.
Record created on 2016-09-06, modified on 2017-01-19