Dunkettle Interchange Upgrade Scheme (Geotechnical)


Location: Cork, Ireland
Client: John Sisk & Son Holdings Ltd.
Status: Active (Ongoing)
Overall Project Value: €120M
Start Date: November 2018
End Date: February 2024

Brief Description

John Sisk & Son Holdings Ltd (Sisk) have been commissioned by Transport Infrastructure Ireland (TII) to develop proposals for the improvement of the existing Dunkettle Interchange.

The Scheme comprises:

  • A series of direct road links between the N8, the N25 and the N40 and links to the R623 Regional Road in Little Island and Burys Bridge in Dunkettle.
  • 1 grade separated junction arrangement at the existing N25 to the east of the existing Dunkettle Interchange.
  • 4 roundabouts – 2 at grade separated junctions and 2 at grade tie ins with the existing road network.
  • 12 major structures of various forms.
  • 24 gantries
  • 9 culverts where the scheme crosses watercourses of intertidal areas.
  • Intelligent Transport Systems.
  • Pedestrian and cyclist facilities.

In addition, the works include the modification of the existing Silversprings junction on the N8 Lower Glanmire Road comprising:

  • Construction of a new raised central reserve on the N8 Lower Glanmire Road.
  • Reconfiguration of the N8 westbound diverge.
  • Reconfiguration of the N8 eastbound merge and diverge.
  • Pedestrian and cycling facilities.


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FT Responsibilities

Sisk appointed FT as Lead Consultant, with Subconsultants Ramboll UK and Clandillon Civil Consulting to carry out the design for the scheme. FT partnered with Ramboll UK for the geotechnical scope of work. The FT Geotechnical team provided key elements of the geotechnical scope of works including:

  • Jointly scoping the Site Investigation and producing specification documents
  • On site supervision of site investigation contractor – including trial pitting, cable percussion, rotary boreholes, geophysical investigation and geo-environmental assessment
  • Groundwater monitoring
  • Joint interpretation of ground investigation data and production of a Ground Investigation Report
  • Liaison with external experts for peer review of design
  • Earthworks design using a variety of ground treatments, including controlled modulus columns, band drains, excavate and replace and surcharging including structural transition zones
  • Foundation design for all structures on the scheme (bridges, retaining walls and gantries), including pile design on soft ground

FT also undertook construction stage support, including provision of geotechnical specialists to the DSR team.

Project Statistics

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Over 600

piles, with a total of over 9,500m of piling

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of Earthworks with over 4km of ground improvements

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boreholes and 50 trial pits carried out

Available positionsCareers

Position Sector Location
Graduate/Project Geotechnical Design Engineer Geotechnical Cork, Dublin or Carlow