About half the distance of the metro line was planned to be underground in two separate bored tunnels. Next to the twin bored (app. 7 m OD) tunnels 7 deep subsurface stations were planned to be executed. The geology of Dublin consists of glacial till deposits overlying Carboniferous bedrock consisting mainly of limestone and shales. The Carboniferous rocks are heavily folded, faulted and jointed. The bedrock level is also strongly undulating. The tunnels and stations were to be constructed largely within the Carboniferous bedrock.
Scope of work
- The construction of geological long sections along the entire alignment on the basis of about 400 soil and rock borings.
- Compilation of a geotechnical interpretative report.
- Preliminary design of TBM alignment and tunnel cross section including preliminary lining design.
- Review of contractors design.
- Design of alternative design of additional 1,5 km of bored tunnels.
- Advise on TBM type in geological conditions varying from silt to coarse sand to Carboniferous rock.
- Geotechnical and Structural design of 5 deep subsurface stations (St. Stephens Green, Parnell Square, Griffith Avenue, Matter, Drumcondra, Airport) within the inner city of Dublin.
- Settlement Risk Assessment studies along the whole underground route of the bored tunnel and along the deep stations.
- Advise on the implementation of mitigation measures such as permeation grouting, jet-grouting and compensation grouting.