Directional core drilling in tunnel construction

1. Directional core drilling in tunnel construction

2. Directional core drilling • Devico AS • Borehole survey systems • Directional core drilling • DeviDrill directional core barrel • First version in 1988 • Present version in 2001 • Projects • Geotechnical exploration • Mineral exploration

3. Geotechnical exploration • Change direction of boreholes • Steer towards targets or keep hole within limits • Retrive core from the most relevant areas

4. Coring along planned tunnel alignment • Continuous rock core • Fault zones • Fractures • Geological anomalies • Rock mechanical properties • Hole for various analysis • Geophysical • Water in-/outflow • Hydraulic fracturing

5. Directional coring in Hong Kong • 4 projects completed last five years • Traffic tunnels (2) • Drainage tunnels (4) • Sewage tunnels (6) • Guidance note from the HK Government • “4.1 Directional drilling techniques are now available to drill from ground level to great depth and then along a horizontal alignment. This method does not require provision of working space at the tunnel level and can be very useful in GI for deep tunnels.”

6. Eagle’s Nest • 2 boreholes • 580 and 1150 meters • 8 m radius tolerance • Borehole between twin tunnels • Fault zones Pressure grouting schedules

7. Harbor Treatment Scheme, Stage II • 6 boreholes • 600 to 1250 meters • 10 x 10m tolerance • Start inclination from -33° to -45°

8. Conclusion • Accurate impression of the rock formations along the tunnel alignment • Security during construction • Stabilization measures • Predict leakage and ground setting • Material estimations • Time & cost estimations • Achieves reliable results, proven in mining and geotechnical exploration projects worldwide

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