Groundwater characterization of a heterogeneous granitic rock massif for shallow tunneling

Authors

  • J. FONT-CAPÓ Institute of Environmental Assessment and Water Research (IDAEA, CSIC). C/ Jordi Girona, 18-26 08034 Barcelona Spain. Phone: +34 934 006 100 Fax: +34 932 045 904. Department of Geotechnical Engineering and Geosciences, Universitat Politècnica de Catalunya (UPC)-BarcelonaTech. C/ Jordi Girona, 1-3 Building D2 08034 Barcelona Spain
  • E. VAZQUEZ-SUÑÉ Institute of Environmental Assessment and Water Research (IDAEA, CSIC). C/ Jordi Girona, 18-26 08034 Barcelona Spain. Phone: +34 934 006 100 Fax: +34 932 045 904.
  • J. CARRERA Institute of Environmental Assessment and Water Research (IDAEA, CSIC). C/ Jordi Girona, 18-26 08034 Barcelona Spain. Phone: +34 934 006 100 Fax: +34 932 045 904.
  • I. HERMS GEOCAT, Gestió de Projectes, S.A. Av. Josep Tarradellas 34-36, 3a Floor 08029 Barcelona, Spain. Phone: +34 93 228 92 53 Fax: +34 93 425 20 01.

Keywords:

Inflow, Shallow tunneling, Fault-zone, Modeling

Abstract

Shallow tunneling may encounter a number of problems, the most important of which is high water inflows in transmissive areas that are often associated with fractures or discontinuities. Moreover, research into shallow tunneling may be limited by the duration and cost of the civil engineering works. Two important aspects that are often overlooked are: variable groundwater behavior of faults (conduit, barrier, conduit-barrier), and role of groundwater connectivity between fractures that cross the tunnel and the rest of the rock massif. These two aspects should be taken into account in the geological and groundwater characterization to correct the tunnel design and minimize hazards. A geological study and a preliminary hydrogeological characterization (including a prior steady state investigation and cross bore-hole tests) were carried out in a granitic sector during the construction of Line 9 of the Barcelona subway (B-20 area). The hydrogeological conceptual model was constructed using a quasi-3D numerical model, and different scenarios were calibrated. Faults and dikes show a conduit-barrier behavior, which partially compartmentalized the groundwater flow. The barrier behavior, which is the most marked effect, is more prominent in faults, whereas conduit behavior is more notable in dikes. The characterization of groundwater media entailed a dewatering plan and changes in the tunnel course. This enabled us to construct the tunnel without any problems.

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Published

2012-12-01

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Section

Articles