A practical geostructural approach for the evaluation of tunnel water inflow by means of FEM seepage analysis

摘要

A practical technical approach for the preliminary evaluation of hydraulic conductivity and tunnel water inflow in fractured rock mass is presented. The procedure is based on the geostructural characterization of the investigated area by means of detailed geostructural field surveys. The principal directions of the anisotropic hydraulic conductivity tensor K are calculated by using the Kiraly equation, integrated with the introduction of the effective hydraulic opening. The water flow into the tunnel planned for excavation under the water table is then estimated by a 2D finite element seepage analysis performed on representative geological cross sections of the tunnel path. In order to verify the reliability of this approach, it has been applied on a 4.5 km length of the Vaglia High Speed Railway Tunnel, excavated a few years ago in order to connect the city of Bologna to the city of Firenze (Italy). The analysis showed that the estimated inflows resulted of the same order of magnitude of the inflows measured in the field.