Tiltmeter Measurements at the Underground Rock Laboratory in Mont Terri

Mont Terri rock laboratory, located in the Swiss Jurassic Mountains, was established with the focus on the investigation and analysys of the properties of argillaceous formations. The scope of Opalinus Clay as a safe, potential option for nuclear waste disposal was broaden, as the behaviour of claystone is of high interest also in the context of caprocks, and hence, for many dynamical processes in the subsurfaces. Extensive research has been performed already for more than 20 years by the partners of the Mont Terri Consortium. These close cooperations cover a broad range of scientific aspects using numerical modelling, laboratory studies, and last not least in-situ experiments. Here, included in the long-term monitoring programme, new investigations apply tiltmeters. Since April 2019, platform tiltmeters have been installed at various locations within the galleries and niches of Mont Terri. The biaxial instruments have resolutions of 1 nrad and 0.1 µrad, respectively (Applied Geomechanics and Lippmann Geophysikalische Messgeräte). The tilt measurements are embedded within various experiments contributing to specific, multiparametrical studies. However, the growing tilt network as a whole will also provide novel information of the rock laboratory. The different time-scales of interest include long-term observations of yearly and decadal variability. So far tilt signals were identified due to excavations during the recent enlargement of the laboratory, earthquake activity (Albania), and local effects. First results of these quasi-continuous recordings will be presented.