Waterview Connection Tunnels

Transcription

1 Hamish Maclean

2 Waterview Connection Tunnels Fissure grouting and rock defect characterisation for the Waterview cross passage tunnels H.J. Maclean, S. Cartwright and A. Giauque S. Cartwright et al, 2017 D. Koumoutsakos et al, 2017 S. France, 2017

3 Project overview NZ Transport Agency project to complete Auckland s 48km Western Ring Route 5 km of 6-lane motorway Direct connection from Auckland Airport to central city NZ s biggest roading construction project ($1.4B budget) Two 2.4km long EPB TBM mainline tunnels (14.5 m dia.) with a concrete segmental lining WATERVIEW CONNECTION AUCKLAND INTERNATIONAL AIRPORT AUCKLAND CBD

4 Project overview WSP

5 Tunnel alignment and cross passages 16 mined cross passages (5m ID) with a in-situ concrete lining Spacing 150m XP temporary support - canopy tubes and fibre reinforced shotcrete Low point sump in XP14

6 Geology East Coast Bays Formation (ECBF) comprising interbedded extremely weak to very weak sandstone and siltstone (typically 1-5MPa). Areas of interbedded weak to moderately strong volcaniclastic grit (Parnell Grit member) and calcite cemented sandstone (typically 10-20MPa). Zone of significantly faulted and folded ground

7 Cross passage excavation in ECBF sandstone

8 Rock mass defects and permeability ECBF permeability is typically dependant on the rock defects. Rock matrix has a very low permeability or around 1 x 10-9 m/s while the rock defects have a comparatively high permeability of around 1 x 10-4 m/s. Storativity and permeability is dependent on the defect characteristics (e.g. persistence and aperture) and the level of connectivity. Typical defect characteristics developed for grout mix design:

9 Probe boreholes at cross passage openings

10 Probe boreholes

11 Probe hole groundwater inflows Project MRs threshold for pre-excavation grouting = Sustained 24 hour inflow exceeding 28 l/min for the 10 m long probe hole. Test location Test results XP Peak inflow 24 hr inflow (l/min) (l/min)

12 High permeability XPs Four at risk XPs identified based on a rock mass defect characteristics and high probe hole inflows XP08, XP10, XP11, XP12. HIGH PERMEABILITY GROUND

13 Pre-excavation grouting Effective grouting of highly permeable rock is reliant on displacing the water in water bearing defects and in-filling the void space with impermeable grout. Accurate characterisation of the range of defects to be grouted was essential to developing a grout mix which penetrated all defects and cut off groundwater inflows. The mix was developed to target the larger aperture faulted joints and crush zones with the potential to also penetrate any tighter joints and bedding plane partings. Cementitious grout using ordinary Portland cement and additives to achieve the viscosity and stability criteria. Single stage grouting with 7.5bar maximum pressure

14 Pre-excavation grouting

15 Pre-excavation grouting results Description Maximum initial groundwater inflow (l/min) Maximum grout volume (l) Maximum pressure (bar) Grout mix (w/c ratio by weight) Final reader hole inflow (l/min) XP08 Primary /1 to 0.8/1 Nil XP08 Tertiary /1 XP10 Primary /1 to 0.8/1 12 XP10 Tertiary /1 to 0.8/1 XP11 Primary /1 to 1/1 1 XP12 Primary /1 to 0.8/1 2 XP12 Secondary /1 to 0.8/1 XP12 Tertiary /1

16 Excavation observations Cementitious grout had permeated both small aperture fractures and wide aperture faulted joints and crush zones Face logging inflow estimates typically less than 3 l/min for each advance

17 Conclusions 1. The permeability of the ECBF rock mass is highly dependent on the presence of water bearing defects. 2. Probe hole flow measurements and characterisation of the rock mass defects at each cross passage was essential to identifying which cross passages needed to be grouted. 3. Accurate characterisation of the range of defects to be grouted was essential to developing an effective grout mix 4. Pre-excavation fissure grouting significantly reduced groundwater inflow into the cross passage excavations. Probe hole flow rates of up to l/min reduced to observed flow rates of 3 l/min. 5. High rock mass permeability of up to around 1x10-4 m/s reduced to approximately 1x10-7 m/s.

18 Acknowledgements New Zealand Transport Agency Well-Connected Alliance Mr Bruce Grant MultiGrout Geotechnical team and Construction Phase Support team