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The connecting gallery: Characterisation of the EDZ

The connecting gallery: Characterisation of the EDZ. Wim Bastiaens – Mol – 27th January ‘04. Overview. EDZ Macro-fractures Second shaft & mounting chamber Connecting gallery Shape & extent Healing & sealing HDZ Conclusions. EDZ. Excavation Damaged Zone OR Excavation Disturbed Zone

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The connecting gallery: Characterisation of the EDZ

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  1. The connecting gallery:Characterisation of the EDZ Wim Bastiaens – Mol – 27th January ‘04

  2. Overview • EDZ • Macro-fractures • Second shaft & mounting chamber • Connecting gallery • Shape & extent • Healing & sealing • HDZ • Conclusions

  3. EDZ • Excavation Damaged Zone OR • Excavation Disturbed Zone • Extent depends on the parameter under consideration: • Macro-fractures (extensive) • HDZ (briefly)

  4. Macro-fractures: shaft

  5. Macro-fractures: shaft

  6. Macro-fractures: Auscultation programme • Fractured zone around shaft: • Mounting chamber (cf. anchoring) • Cored boreholes (2) • Seismic campaign: • Cross-hole measurements • Down-hole measurements • During excavation: fracture observation • Consistent results

  7. an excavation-induced fracture plane borehole 2001-2 interval velocity measurements cross hole measurements cored boreholes borehole 2000-4 borehole 2000-11 borehole 2000-5 seismic campaign

  8. Macro-fractures: Auscultation programme * Cores * Seismic * Observation

  9. Macro-fractures: connecting gallery • Fracture observation: • Front • Sidewalls (unsupported zone) • Consistent fracture pattern • Except begin (shaft) and end (Test Drift) • No pre-existing fractures observed • Digital map of fracture traces on walls

  10. Macro-fractures: connecting gallery • Fracture observation: • Front • Sidewalls (unsupported zone) • Consistent fracture pattern • Except begin (shaft) and end (Test Drift) • No pre-existing fractures observed • Digital map of fracture traces on walls

  11. Macro-fractures: connecting gallery • Fracture observation: • Front • Sidewalls (unsupported zone) • Consistent fracture pattern • Digital map of fracture traces on walls

  12. Macro-fractures: extent • Radial: ~1 m • cored boreholes • Axial: ~6 m • Observations (near Test Drift, cf. later) • Modelling

  13. Excavation Differential stress Fractures Macro-fractures: origin Fracture criteria (ex. Mohr Coulomb)

  14. Macro-fractures: origin

  15. Macro-fractures: comparison • Connecting gallery vs. shaft • Similar shape (not same) • Different extent (cf. convergence)

  16. Comparison • Connecting gallery vs. Test Drift: • Similar pattern: mirror • ~6 metres (axial) • Oxidation only in last metre: • Sealing • Re-activation

  17. Healing / sealing: qualitative evidence • Oxidation at connection: • ~6 m fractures • ~1 m oxidised • Disappeared uncased borehole: • Borehole from starting chamber, uncased • Impossible to visually locate during excavation • Partly healed cores: • Radial cores in EDZ • Fractures re-appear after manipulation or drying • Pressure build-up • Install piezometer (borehole, 50% oversize) • Measure pore water pressure at 0.6 m (after 14 months) • Borehole seals off filter & no interconnected fractures • Lab testing: • Artificial fracture => water flow (K-testing) • Restoration of mechanical strength

  18. HDZ • Pore water pressure: • Large influenced zone • Anisotropic behaviour • RH = ~20 m • RV > 40 m • Hydraulic conductivity • 5 m: unchanged (~10-12) • Closer: 2004

  19. HDZ • Pore water pressure: • Large influenced zone • Anisotropic behaviour • RH = ~20 m • RV > 40 m • Hydraulic conductivity • 5 m: unchanged (~10-12) • Closer: 2004

  20. Conclusions • EDZ characterised • Fractures: • Unavoidable • Limit their extent • Sealing / healing evidences • EC SELFRAC project (EURIDICE, NAGRA, SOLEXPERT, G3S, UJF, KUL,UPFL) • EDZ cut-off in plastic clays necessary? • HDZ • Large extent • Hydraulic conductivity

  21. Questions ?

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