Full Scale Hydraulic Response of Opalinus Clay to Tunneling, Ventilation, and Heating – Investigations of the FE-Experiment at the Mont Terri underground research laboratory in Switzerland

Tobias Vogt1, Herwig R. Müller1, Benoit Garitte1, Toshihiro Sakaki1, Tim Vietor1
1 Nagra

O 4.4 in Final repositories and underground disposal sites

15.04.2016, 10:30-10:45, Audimax A, Geb. 30.95

The Full-Scale Emplacement (FE) Experiment at the Mont Terri underground research laboratory in Switzerland is a full-scale multiple heater test in Opalinus Clay. Based on the Swiss disposal concept it simulates the construction, emplacement, backfilling, and early post-closure thermo-hydro-mechanical (THM) evolution of a spent fuel / vitrified high-level waste repository tunnel in a realistic manner. The main aim of this experiment is to investigate at full scale repository-induced THM coupled effects onto the host rock and to validate existing coupled THM models. A further aim is to gather experience with full-scale tunnel construction and associated hydro-mechanical (HM) processes in the host rock.

The entire experiment implementation (in a 50 m long gallery with approx. 3 m diameter) as well as the early post-closure THM evolution are monitored using a network of several hundred sensors (state-of-the-art sensors and measurement systems as well as fiber-optic sensors). The sensors are distributed in the host rock's near- and far-field, the tunnel lining, the engineered barrier system, which consists of bentonite pellets and blocks, and on the heaters.

We will present the full scale hydraulic response of Opalinus Clay to tunneling, ventilation, and heating. In particular, we investigated the excavation induced hydraulic response of the host rock. Therefore, the spatiotemporal evolution of porewater-pressure time series was closely analyzed to get a better understanding of HM coupled processes during and after the excavation phase as well as the impact of anisotropic geomechanic and hydraulic properties of Opalinus Clay on its hydraulic behavior. Excavation related investigations were completed by means of inclinometer data to characterize the non-elastic and time-dependent deformations. In addition, we evaluated the effect of drainage and suction processes during the ventilation phase on the pressure distribution in the host rock. The rock-mass close to the tunnel wall behaves differently depending on type of tunnel support. Where Opalinus Clay is supported only by steel arches without shotcrete, seasonal fluctuations in saturation are observed in shallow depths that were analyzed further by time-series analysis tools to better understand the anisotropic hydraulic properties of Opalinus Clay in the unsaturated zone. The heating phase of the FE Experiment started in February 2015. Therefore, we will present results of the first year of heating with regard to spatiotemporal water fluxes in the engineered barrier system and triggered THM processes in the rock. Based on the new findings in our results the conceptual models of HM and THM processes and hydraulic behavior of clay rich formations during excavation, ventilation, and early post-closure (heating) phases will be improved. 

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