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pure and applied geophysics

, Volume 159, Issue 1–3, pp 179–195 | Cite as

The Assessment of Damage Around Critical Engineering Structures Using Induced Seismicity and Ultrasonic Techniques

  • .S. Pettitt
  • C. Baker
  • R.P. Young
  • L.-O. Dahlström
  • G. Ramqvist

Abstract 

— Two large-diameter boreholes have been excavated vertically from the floor of a tunnel at the Äspö Hard Rock Laboratory, Sweden. The two deposition holes will have simulated high-level radioactive waste canisters installed in them in an experiment undertaken to test the retrievability of waste from a proposed repository. Induced seismicity and other acoustic monitoring techniques have been used to investigate the Excavation Damaged Zone (EDZ) around the two holes. High-frequency acoustic emission (AE) monitoring has been used to delineate regions of stress-induced microfracturing on the millimetre scale. This has been shown to locate in clusters around the perimeter of the deposition hole at azimuths orthogonal to the far-field maximum principal stress. Three-dimensional velocity surveys have been conducted along ray paths that pass through the damaged region and through a stress-disturbed zone around the excavation. Induced microfracturing and stress disturbance have been observed as sharp decreases in velocity as the excavation proceeds through the rock mass. The combination of the high-resolution velocity measurements and the AE source locations has allowed the linking of the velocity measurements to a volume of excavation damaged rock. This has provided a quantitative estimate of the effect of the EDZ on the rock mass.

Key words: Excavation damage, microcracking, borehole breakout, acoustic emission, micro-velocity. 

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Copyright information

© Birkhäuser Verlag Basel, 2002

Authors and Affiliations

  • .S. Pettitt
    • 1
  • C. Baker
    • 1
  • R.P. Young
    • 2
  • L.-O. Dahlström
    • 3
  • G. Ramqvist
    • 4
  1. 1.Applied Seismology Consultants, 10 Belmont, Shrewsbury, UK. E-mail: will@seismology.orgGB
  2. 2.Applied Seismology Laboratory, Department of Earth Sciences, Liverpool University, Liverpool, UK. E-mail: r.p.young@liverpool.ac.ukGB
  3. 3.NCC Tecnik, Gothenburg, 40514 Sweden. E-mail: lars-olof.dahlstrom@ncc.seSE
  4. 4.SKB Äspölaboratoriet, Figeholm, 57295 Sweden. E-mail: gunnar.ramqvist@skb.seSE

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