A multi-method investigation of the permeability structure of brittle fault zones with ductile precursors in crystalline rock

Grundwasser, vol. 29, pp. 49–61

Abstract

Abstract Brittle faults and fault zones are among the most hydraulically active elements in predominantly impermeable crystalline host rock. They pose a significant challenge to underground infrastructure like nuclear waste repositories. Brittle fault zones frequently occur along pre-existing ductile shear zones as they introduce weakness planes in the rock. Four brittle fault zones of ductile origin were analyzed in the Rotondo Granite at the “BedrettoLab” in the Swiss Central Alps. Scanline mapping, rock sampling and permeability measurements using three different methods provide detailed insights into the heterogeneous fault zone architecture and hydrogeology. Average intact rock permeability is in the range of 10−19 to 10−17 m2. Fluid flow is channeled into single open or partially mineralized fractures of, at point-scale, up to 10−14 m2, demonstrated by selective gas probe permeameter measurements and borehole hydraulic testing. Reduced permeabilities have been measured in close proximity to these permeable features, indicating alteration of and around the fracture walls.

Authors 6

1. Julian Osten corresponding Aachen Department of Engineering Geology and Hydrogeology

   RWTH Aachen University

   Affiliation as printed

   Department of Engineering Geology and Hydrogeology, RWTH Aachen University, Lochnerstraße 4–20, 52064, Aachen, Germany

   Department of Engineering Geology and Hydrogeology, RWTH Aachen University, Lochnerstraße 4–20, 52064, Aachen, Germany

2. Tom Schaber Aachen Department of Engineering Geology and Hydrogeology

   RWTH Aachen University

   Affiliation as printed

   Department of Engineering Geology and Hydrogeology, RWTH Aachen University, Lochnerstraße 4–20, 52064, Aachen, Germany

   Department of Engineering Geology and Hydrogeology, RWTH Aachen University, Lochnerstraße 4–20, 52064, Aachen, Germany

3. Garri Gaus Aachen Institute for Geology and Geochemistry of Petroleum and Coal

   RWTH Aachen University

   Affiliation as printed

   Institute for Geology and Geochemistry of Petroleum and Coal, RWTH Aachen University, Lochnerstraße 4-20, 52064, Aachen, Germany

   Institute for Geology and Geochemistry of Petroleum and Coal, RWTH Aachen University, Lochnerstraße 4-20, 52064, Aachen, Germany

4. Pooya Hamdi Aachen Department of Engineering Geology and Hydrogeology

   RWTH Aachen University

   Affiliation as printed

   Department of Engineering Geology and Hydrogeology, RWTH Aachen University, Lochnerstraße 4–20, 52064, Aachen, Germany

   Department of Engineering Geology and Hydrogeology, RWTH Aachen University, Lochnerstraße 4–20, 52064, Aachen, Germany

5. Florian Amann Aachen Department of Engineering Geology and Hydrogeology

   RWTH Aachen University · Fraunhofer Research Institution for Energy Infrastructures and Geotechnologies IEG

   Affiliation as printed

   Department of Engineering Geology and Hydrogeology, RWTH Aachen University, Lochnerstraße 4–20, 52064, Aachen, Germany

   Fraunhofer Research Institution for Energy Infrastructures and Geothermal Systems IEG, Kockerellstraße 17, 52062, Aachen, Germany

   Fraunhofer Research Institution for Energy Infrastructures and Geothermal Systems IEG, Kockerellstraße 17, 52062, Aachen, Germany

6. Peter Achtziger-Zupančič Aachen Department of Engineering Geology and Hydrogeology

   RWTH Aachen University

   Affiliation as printed

   Department of Engineering Geology and Hydrogeology, RWTH Aachen University, Lochnerstraße 4–20, 52064, Aachen, Germany