First Assessment by Groundwater Modelling of the water influx in cavities linked to the future underground Einstein Telescope in the three borders region (D, NL, Be)

Abstract

In the three borders region of Belgium, The Netherlands and Germany a gravitational waves observation centre named Einstein Telescope project is under consideration. The centre would consist mainly in three underground cavities linked by three tunnels forming a triangle with 10 km sides. This master thesis work has the aim of studying the water influx induced by the construction of the Einstein Telescope. As a first step, the present work is focused on the numerical simulation of the groundwater around the future cavities and tunnels. The model is carried out with the use of GMS-MODFLOW using the finite difference technique. Two conceptual models have been simulated. A first conceptual model has been simulated with the presence of the underground cavities (corresponding to one of the triangle corner) and the sensitivity analysis has been performed to show how the model is sensitive to the change of parameters such as the hydraulic conductivity of the geological media and the conductance of the drains, representing the cavities. The study of the induced groundwater flow has been done for three different cases with the designed hydraulic conductivity of the different geological formations. Then, an additional sensitivity analysis has been performed changing the hydraulic conductivity of all the geological formations with the exception of the one containing the simulated cavity. Another scenario has been simulated with the presence of one underground tunnel, for predicting the groundwater quantity that will be drained by a typical tunnel section. The modelling of the tunnel has been done for showing the response of the groundwater flow model in terms of drained flow. In both models, the drawdown has been also estimated. In fact, it represents the difference between the piezometric heads related to the condition prior the installation of the cavities or the tunnel and the computed piezometric heads in steady-state with the presence of them. In this way, the impact that the underground cavities/ tunnel have on groundwater has been evaluated.