Test of the method indirect prediction ahead of water bearing zones with temperature data with the measured data from the Lötschberg-Basistunnel (FGU2005/001)
Overview
Background & policy context:
The spatial temperature field in the subsurface is influenced by water circulating in extended zones with a natural velocity of more than 10-8 m/s (~1 m/year). Principally this allows to characterize to some extent the hydrogeological conditions by rock temperatures measured along the excavated tunnel. Within the research project FGU2003-003 it has been demonstrated that the order of magnitude of the water inflow to be expected can be evaluated by interpretation of measured rock temperatures in the tunnel. This evaluation has been carried out on purely theoretical basis using a standardized model of a rock mass. Now this method of prediction ahead shall be tested with data for temperature and water inflow measured during the advance of the Lötschberg Base Tunnel. Following the principal procedure of the method a three-dimensional FE-model of the region must be build up in a first step. The model has to include the topography and all the principal, thermal relevant units. In a second step the prediction of the range of possible water inflow following the tunnel trace in constant steps will be carried out using the measured rock temperatures. These scenarios of water inflows will be finally compared with the corresponding measured values.
Objectives:
In the frame of the previous research project FGU2003-003 it has been demonstrated on theoretical basis that the order of magnitude of a possible water inflow into the tunnel can be determined by numerical interpretation of measured rock temperatures. In the presented project, the evaluation of this method of prediction ahead has been carried out with a simple model. Now the method shall be tested with real data for rock temperature and water inflows measured during the advance of the Lötschberg-Basistunnel.
Methodology:
In the calculations it is basically three-dimensional finite element modeling with the program FRACTURE the GEOWATT AG. Here, the automatic model generator which was optimized within the framework of the research project FGU2003-003 is used for the preparation of various water-bearing fault zones.
The project will be developed during the following phases:
Phase 1: preparation of metrics
Phase 2: Creation of the 3D finite element model of the area of the Lötschberg base tunnel and calibration
Phase 3: Calculation of water intrusion scenarios
Phase 4: Evaluation
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