Wide-area hydrogeological modelling for the Brenner Base Tunnel / Großflächige hydrogeologische Modellierung für den Brenner Basistunnel

The planned tunnel alignment of the Brenner Base Tunnel crosses the aquifer of the Hochstegen marble between the Valsertal and Pfitschtal valleys. Due to the great importance of this aquifer for the water balance of the affected gullies, a 2D model was produced of the groundwater flow system. The intention of the 2D model was on one hand to gain information about the effects of the lowering of the groundwater table by the draining effect of the tunnel holes. Another intention of the model was to investigate whether the lowering of the groundwater table could be kept to a small and acceptable extent through a suitable grouting campaign and thus keep the influence on the groundwater balance in the model area small. Starting with the experience gained with grouting during the construction of the Lötschberg and the Gotthard Base Tunnels, which had been able to considerably reduce the permeability in the area around the tunnel bores, calculations were performed with the finite difference program Modflow, in which the effect of a grouted ring around the tunnel holes was investigated in detail. With the calculations, it was possible to demonstrate that the lowering of the groundwater table in the vicinity of the aquifer of the Hochstegen marble can be reduced to a small, acceptable extent. The article deals with the model, the hydraulic parameters, the values from experience for grouting measures or their effects on the modelling parameters and describes in detail the knowledge gained. © 2014 Ernst & Sohn Verlag für Architektur und technische Wissenschaften GmbH & Co. KG, Berlin.