HR: 0800h
AN: H11D-1305    [Abstracts]
TI: 3D Hydrogeological Modeling of Impact from Tunneling
AU: * Kohl, T
EM: kohl@geowatt.ch
AF: GEOWATT AG, Dohlenweg 28, Zurich, 8050 Switzerland
AU: M‚gel, T
EM: megel@geowatt.ch
AF: GEOWATT AG, Dohlenweg 28, Zurich, 8050 Switzerland
AB: With the goal of reproduction the subsurface flow paths for an environmental impact study a three-dimensional hydraulic model of an major Austrian tunnel was developed in 2001 in a first phase. The model encompassed a regional scale of more than 1000 km2. Therewith, the combined geological, hydraulic and geothermal situation as well as hydrogeologically critical zones along the tunnel axis could be highlighted. Based on a further elaborated regional geological / hydrogeological conceptual model, a 2nd project phase started in 2004 with an even more sophisticated regional model that concentrates on the near tunnel realm. In the vicinity of the tunnel, a strongly refined numerical finite element mesh allows the calculation of the strong hydraulic gradients that develop near the tunnel wall. The model now includes the tunnel construction with a defined diameter and follows the path of the tunnel axis. Therefore, the full three-dimensionality of the construction and the recognized geological / hydrogeological structures are integrated in a single numerical model. In the case of this project two models have been developed, one each for the area East and West of the divide along the Mountain allowing the simulation to cover the total tunnel length of approx.45 km. In parallel, the model includes the hydrogeological findings from various investigation boreholes and the infiltration from measuring campaigns performed to date. The definition of hydraulic boundary conditions turned out to have the largest influence on the quality of the numerical results. By adopting a strategy that defines both Neuman (at higher altitude range) and Dirichlet boundary conditions (at lower altitude range) this problem was well treated. In our contribution, it is demonstrated that a mesh of nearly half a million nodes can be set up that accounts for nearly arbitrary geological settings but also for the refined representation of subsurface constructions. It may be noted that these accomplishments need to be combined with an adequate finite element formulation. In our case, the treatment of a series of element types (in 3D: hexahedrons, pyramids, tetrahedrons or prisms) is indispensable. This way, the further impact on poroelastic processes like subsidence can also simulated.
DE: 1832 Groundwater transport
DE: 2753 Numerical modeling
DE: 4536 Hydrography and tracers
SC: Hydrology [H]
MN: Fall Meeting 2005