Modeling of damage,permeability changes and pressure responses during excavation of the TSX tunnel in granitic rock at URL,Canada |
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| Authors: | Jonny Rutqvist Lennart Börgesson Masakazu Chijimatsu Jan Hernelind Lanru Jing Akira Kobayashi Son Nguyen |
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| Institution: | (1) Earth Sciences Division, Lawrence Berkeley National Laboratory, MS 90-1116, Berkeley, CA 947 20, USA;(2) Clay Technology AB, Lund, Sweden;(3) Hazama Cooperation, Tokyo, Japan;(4) FEM Tech AB, Gothenburg, Sweden;(5) Royal Institute of Technology, Stockholm, Sweden;(6) Kyoto University, Kyoto, Japan;(7) Canadian Nuclear Safety Commission, Ottawa, ON, Canada |
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| Abstract: | This paper presents numerical modeling of excavation-induced damage,
permeability changes, and fluid-pressure responses during excavation of a test tunnel associated with the tunnel
sealing experiment (TSX) at the Underground Research Laboratory (URL) in Canada. Four
different numerical models were applied using a wide range of approaches to model damage
and permeability changes in the excavation disturbed zone (EDZ) around the tunnel.
Using in situ calibration of model parameters, the modeling could reproduce observed
spatial distribution of damage and permeability changes around the tunnel as a
combination of disturbance induced by stress redistribution around the tunnel
and by the drill-and-blast operation. The modeling showed that stress-induced
permeability increase above the tunnel is a result of micro and macrofracturing
under high deviatoric (shear) stress, whereas permeability increase alongside
the tunnel is a result of opening of existing microfractures under decreased mean
stress. The remaining observed fracturing and permeability changes around the periphery
of the tunnel were attributed to damage from the drill-and-blast operation. Moreover,
a reasonably good agreement was achieved between simulated and observed
excavation-induced pressure responses around the TSX tunnel for 1 year following its
excavation. The simulations showed that these pressure responses are caused by
poroelastic effects as a result of increasing or decreasing mean stress, with
corresponding contraction or expansion of the pore volume. The simulation results
for pressure evolution were consistent with previous studies, indicating that the
observed pressure responses could be captured in a Biot model using a relatively
low Biot-Willis’ coefficient, α ≈ 0.2,
a porosity of n ≈ 0.007, and a relatively
low permeability of k ≈ 2 × 10−22 m2,
which is consistent with the very tight, unfractured granite at the site. |
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| Keywords: | Coupled processes Excavation disturbed zone Damage Permeability TSX |
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