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A55 North Wales Coast Road

A55 North Wales Coast Road

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A55 North Wales Coast Road

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  1. A55 North Wales Coast Road Jemma Oakley & Hannah Grimley

  2. Introduction • 145km dual carriageway from Chester to Holyhead • Diverse geological terrains-glacial features, abandoned mines & igneous rock intrusions

  3. Location Map

  4. Holywell Bypass • 9km dual carriageway, completed in 1986 • Two main geo-engineering features 1)Cutting through glacial deposits 2)Abandoned mines & mineral veins

  5. Holywell BypassGlacial Geology • 16m deep cutting through sand & gravel layer which was sandwiched between clayey tills. • Low permeability of the upper till layer • High groundwater pressures • Drainage to lower groundwater pressures

  6. Holywell BypassAbandoned mines • 36% of route affected by mining of lead, zinc & silver ceased in early 20th century • Abandoned mine-collapse of unsupported mineshafts & subsidence due to subsurface workings in mineral veins

  7. Distribution of mineral veins along A55 Holywell Bypass

  8. Holywell Bypass Mining investigations • Few records • Specialist mining consultants • Historical documents, old mining records & maps • CCTV & mine access

  9. Holywell BypassMining Solutions • 34 mineshafts capped at rockhead • Mineworkings & mineral veins spanned by reinforced concrete rafts • Continuous annual monitoring

  10. Pen-y-Clip Tunnel

  11. Pen-y-Clip Tunnel • Mountainous headland creating a natural obstacle • Scheme completed 1994. 1.9km in total • Tunnel – 930m long • Geologically – Igneous intrusion of Upper Ordovician age (~450 Ma)

  12. Pen-y-Clip Tunnel

  13. Pen-y-Clip Tunnel • Construction - very heavily jointed - central section shorter than anticipated • Joints – excavated and supported • Central zone – driven and blasted

  14. Pen-y-Clip Tunnel • Still concerns about rockfalls • Rockfall countermeasures

  15. Conclusion • 32 yr project • Encountered many geological problems • Constant monitoring ensures future safety • Findings enhance future schemes

  16. References • ‘Geo-engineering along the A55 North Wales Coast Road’. D.Nichol. Quarterly Journal of Engineering Geology and Hydrology. • www.soil.co.uk/AppHTunn.htm • http://www.nwales-traffic.co.uk/english/road/road_users/highways_pages/newtra/hwell_bypass.asp • http://www.nwales-traffic.co.uk/english/road/road_users/highways_pages/newtra/penyclip2.asp