Einstein-Telescope in the Euregio-Meuse-Rhine - Preliminary engineering geological site characterization for siting and design

Modern gravitational-waves astronomy is moving underground. Geological units act as noise-dampening covers to isolate highly sensitive gravitational-wave detectors from ambient noise disturbances, which poses challenges for the siting, planning, and construction of detectors. The current feasibility study for the Einstein Telescope (ET), the European third-generation gravitational-waves detector, aims to find the most suitable site for construction and operation from various perspectives. One potential site is the Euregio-Meuse-Rhine (EMR) area in the border region between the Netherlands, Belgium, and Germany. The Einstein Telescope is planned as a large-scale underground infrastructure with over 30 km of tunnels and various cavern constructions, approximately 250 m below the surface. This paper presents the preliminary results of the first site characterization phase for this site from an engineering geological perspective. The results show (1) complex geological conditions of siliciclastic and carbonate, brittle and hard Paleozoic (Frasnian to Westphalian) rocks beneath a cover of soft, partly unconsolidated Cretaceous and Cenozoic sediments, (2) the strong influence of several tectonic events, especially the thrust-and-fault belt of the Variscan Front and the opening of the Lower Rhine Graben, (3) variable and in places high hydraulic conductivities (10- 5 m/s) and, (4) variable rock mechanical properties of potential host rock formations (e.g. Famennian and Namurian rocks). Finally, an engineering geological assessment of the suitability, challenges, and requirements for future work associated with the construction of the ET in the EMR region is presented.