Performance of the Opalinus Clay under thermal loading: experimental results from Mont Terri rock laboratory (Switzerland)

The final publication is available at Springer via http://dx.doi.org/10.1007/s00015-016-0258-8The paper presents an overview of the behaviour of Opalinus Clay under thermal loading as observed in three in situ heating tests performed in the Mont Terri rock laboratory: HE-B, HE-D and HE-E. The three tests are summarily described; they encompass a broad range of test layouts and experimental conditions. Afterwards, the following topics are examined: determination of thermal conductivity, thermally-induced pore pressure generation and thermally-induced mechanical effects. The mechanisms underlying pore pressure generation and dissipation are discussed in detail and the relationship between rock damage and thermal loading is examined using an additional in situ test: SE-H. The paper concludes with an evaluation of the various thermo-hydro-mechanical (THM) interactions identified in the heating tests.Peer ReviewedPostprint (author's final draft

Performance of the Opalinus Clay under thermal loading: experimental results from Mont Terri rock laboratory (Switzerland)

The final publication is available at Springer via http://dx.doi.org/10.1007/s00015-016-0258-8 The paper presents an overview of the behaviour of Opalinus Clay under thermal loading as observed in three in situ heating tests performed in the Mont Terri rock laboratory: HE-B, HE-D and HE-E. The three tests are summarily described; they encompass a broad range of test layouts and experimental conditions. Afterwards, the following topics are examined: determination of thermal conductivity, thermally-induced pore pressure generation and thermally-induced mechanical effects. The mechanisms underlying pore pressure generation and dissipation are discussed in detail and the relationship between rock damage and thermal loading is examined using an additional in situ test: SE-H. The paper concludes with an evaluation of the various thermo-hydro-mechanical (THM) interactions identified in the heating tests

High-resolution mini-seismic methods applied in the Mont Terri rock laboratory (Switzerland)

We present several mini-seismic methods developed and applied in recent years in the Mont Terri rock laboratory. All these applications aimed at correlating and interpreting seismically derived parameters with relevant rock-mechanical parameters and findings. The complexity of the local site setting always required very high spatial and parameter resolution. Both, seismic P- and S-wave velocities and dynamic elastic parameters, such as the dynamic Poisson’s ratio υdyn and the Young’s modulus Edyn, are used to characterise the Opalinus Clay under real in situ conditions. We were able to establish a correlation between static and dynamic elastic Young’s moduli. We describe the extremely large, small-scale variability of seismic parameters normal and parallel to the bedding plane orientation and address the question of fracture detection. We also present examples of the characterization of excavation-damaged zones with seismic parameters, including extent as well as degree of damage, and compare these to geological and structural mapping. The evolution of borehole-disturbed zones (BdZ) was deduced from repeating high-resolution borehole measurements. Finally, we quantify seismic anisotropy at dimensions between several cm and tens of m.ISSN:1661-8734ISSN:1661-872

High-resolution mini-seismic methods applied in the Mont Terri rock laboratory (Switzerland)

We present several mini-seismic methods developed and applied in recent years in the Mont Terri rock laboratory. All these applications aimed at correlating and interpreting seismically derived parameters with relevant rock-mechanical parameters and findings. The complexity of the local site setting always required very high spatial and parameter resolution. Both, seismic P- and S-wave velocities and dynamic elastic parameters, such as the dynamic Poisson’s ratio υdyn and the Young’s modulus Edyn, are used to characterise the Opalinus Clay under real in situ conditions. We were able to establish a correlation between static and dynamic elastic Young’s moduli. We describe the extremely large, small-scale variability of seismic parameters normal and parallel to the bedding plane orientation and address the question of fracture detection. We also present examples of the characterization of excavation-damaged zones with seismic parameters, including extent as well as degree of damage, and compare these to geological and structural mapping. The evolution of borehole-disturbed zones (BdZ) was deduced from repeating high-resolution borehole measurements. Finally, we quantify seismic anisotropy at dimensions between several cm and tens of m.ISSN:1661-8734ISSN:1661-872

CO2 Long-term Periodic Injection Experiment at the Underground Rock Laboratory, Mont Terri

Peer reviewe

CO2 long-term periodic injection experiment at Mont Terri (CO2LPIE)

Peer reviewe

In-situ shear modulus determination by pressuremeter tests in opalinus clay and reconciliation with laboratory tests

Opalinus Clay is the designated host rock for a deep geological repository of radioactive waste in Switzerland. The determination of its geo-mechanical properties relies heavily on laboratory tests on small specimens. To assess the in-situ elastic stiffness at a larger scale, pressuremeter tests were performed in Opalinus Clay at the Mont Terri Rock Laboratory, with the testing probe oriented both perpendicular and parallel to the bedding planes. The shear modulus of the Opalinus Clay is determined using the unload data of the pressuremeter tests in different lithofacies and at multiple expansion pressure levels. The measured shear modulus is dependent on the expansion pressure at the initial stage of the test but approaches a relatively constant value when a pressure magnitude of about 5 MPa is reached. The stiffness anisotropy of the Opalinus Clay, the rock mass disturbance, and the local fractures at test intervals can affect the measured moduli. In this test program, the impact of lithofacies was not evident at low expansion pressures and could not be evaluated at a greater expansion pressure. The shear modulus of the Opalinus Clay exhibits a nonlinear dependence on strain increment, which can be interpreted using a power-law stress–strain relationship. The small-strain nonlinearity is also dependent on the expansion pressures for the Opalinus Clay. At expansion pressures greater than 5 MPa, the strain-dependent shear moduli obtained from pressuremeter tests are comparable with those determined by triaxial tests on intact core specimens. At the shear strain increment of 0.1%, a secant shear modulus (parallel to bedding) of approximately 3 GPa for the intact Opalinus Clay can be concluded from both the pressuremeter and triaxial tests