Effect of tunnel excavation on transmissivity distributions and flow in a fracture zone

  • Author(s) / Creator(s)
  • Abstract: During an excavation-response experiment performed at the Underground Research Laboratory (Atomic Energy of Canada Limited, Pinawa, Man.) a decrease in fracture-zone transmissivity was measured as a tunnel intersected the room 209 fracture zone. The decrease in transmissivity was greatest as the pilot and the slash faces passed the fracture zone. The transmissivities increased towards their preexcavation values as the faces proceeded past the fracture zone. This response suggested that shear stresses or displacements controlled the hydraulic behaviour of the fractures. The hydraulic response in the fracture zone was analyzed using finite element models. Predictions of shear-displacement distributions in the fracture zone as a function of face position were obtained from a three-dimensional finite element model using joint elements to represent the fracture zone. A phenomenological relationship between shear displacement and transmissivity change was used to modify the transmissivity distributions in the fracture zone based on shear displacements for different excavation stages. Seepage analyses with these transmissivities provided predictions that matched closely the field measurements obtained from the room 209 fracture zone. These results and the inability of conventional, normal stress dependent, fracture closure to predict consistently the hydraulic response support the concept of shear causing a reduction in fracture-zone transmissivity. Excavation-dependent, shear-induced reduction in transmissivity provides an alternate mechanism for interpreting and understanding the hydraulic response of disturbed fracture zones.

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    Article (Published)
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    © 1993 NRC Research Press (Canadian Science Publishing). This version of this article is open access and can be downloaded and shared. The original author(s) and source must be cited.
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  • Citation for previous publication
    • Tannant, D. D., Kaiser, P. K., & Chan, D. H. (1993). Effect of tunnel excavation on transmissivity distributions and flow in a fracture zone. Canadian Geotechnical Journal, 30(1), 155.