Fracture processes and in-situ fracture observations in Gipskeuper

Several tunnels constructed in sulfate-rich clay rocks revealed severe and costly problems associated with floor heave as a consequence of gypsum precipitation. Previous studies have shown that gypsum precipitation often takes place within pre-existing natural structures or fissures which were created by hoop-stresses and opened as a consequence of radial stress relief. Brittle fracture processes cause a damage zone around an underground excavation in sulfate-rich clay rock when the stress exceeds the crack initiation threshold. Microcracks in the damage zone are seen as a preconditioning factor for gypsum precipitation when sulfate-rich fluids penetrate these fissures and become supersaturated. However, brittle failure pro-cesses in sulfate-rich clay rocks and the stress magnitudes required to initiate microcracks were previously not studied in detail, and the hypothesis of brittle fracturing as a major cause for swelling has not been conclusively proven. It was also not studied in detail newly formed fractures actually exist in the vicinity of tunnels in this rock type, and if these fracture may be related to stress fracturing or unloading or propagation of pre-existing discontinuities. Furthermore, the influence of newly formed fractures on fluid flow and gypsum precipitation was not demonstrated. ln this study we test these hypotheses with data from new boreholes and cores drilled into the Gipskeuper formation intersected by the Belchen tunnel in the Swiss Jura Mountains. The investigation primarily focuses on the stress magnitude at which microcracks initiate in Anhydrite-Clay rocks, on factors such as heterogeneities that affect the fracturing processes and strength, and on micro-structural observations below the invert of the Belchen drainage tunnel. This investigation provides insights into the fracture formation mechanisms and its influence on preferential pathways for fluid flow and gypsum precipitation.

• Corporate Authors:

  BUNDESAMT FUER STRASSENBAU (ASTRA) / OFFICE FEDERAL DES ROUTES (OFROU)

  MUEHLESTRASSE 2, ITTIGEN
  BERN,   Switzerland  CH-3003
• Authors:
  • AMANN, F
  • UEDUEL, O
  • LOEW, S
  • KAISER, P
• Publication Date: 2013-8

Language

• English

Media Info

• Pagination: 67P
• Serial:
  • Issue Number: 1422

Subject/Index Terms

• TRT Terms: Boreholes; Clay; Core samples; Cracking; Failure; Flow; Fluid dynamics; Fractures (Anatomy); Gypsum; Laboratories; Mathematical analysis; Research reports; Rock mechanics; Rocks; Stresses; Surveillance; Theory
• ITRD Terms: 6471: Analysis (math); 9078: Assumption; 5711: Bore hole; 4177: Clay; 9101: Control (surveillance); 5700: Core (boring); 5211: Cracking; 5211: Crazing; 5520: Failure; 5211: Fissuring; 5430: Flow (fluid); 2161: Fracture (bone); 4175: Gypsum; 9078: Hypothesis; 9101: Inspection; 6237: Laboratory (not an organization); 9101: Observation; 8559: Research report; 4154: Rock; 5757: Rock mechanics; 5575: Stress (in material); 9101: Supervision
• Subject Areas: Geotechnology; I54: Construction of Tunnels;

Filing Info

• Accession Number: 01506309
• Record Type: Publication
• Source Agency: Ecole Polytechnique Fédérale de Lausanne (EPFL)
• Files: ITRD
• Created Date: Jan 31 2014 2:14PM