N4 Collooney to Castlebaldwin Road Scheme


Location: Co. Sligo
Client: Sligo County Council
Project Value: €100 million
Country: Ireland

The Proposed Road Development for the N4 between Collooney and Castlebaldwin in Co. Sligo is 14.7km in length and is comprised of:

  • 2.6km of widening and improvement of the existing single carriageway to a Type 2 Dual Carriageway between the townlands of Collooney/Toberbride and Doorly; and
  • 12.1km of offline realignment from Doorly to Cloghoge Lower, south of Castlebaldwin village (11.2km between Doorly and Castlebaldwin is proposed to be Type 2 Dual Carriageway and the remaining tie-in section with the existing N4 is proposed to be Type 1 Single Carriageway);

AGL Consulting provided geotechnical advice through Phases 3-5 of the scheme development in accordance with the 2010 Transport Infrastructure Ireland (NRA) Project Management Guidelines, i.e.:

Phase 3 – Schematic Design
Phase 4 – Environmental Impact Assessment & The Statutory Processes
Phase 5 – Advance Works & Construction Documents Preparation

Our scope of services has included the following:

  • Preparation of the scope of work, specification and contract documents for Phase II of the preliminary ground investigations and provision of technical support during the fieldwork stage of the contract, including lab test scheduling.
  • Preparation of a geotechnical report for preliminary design of the scheme to interpret ground and groundwater conditions.
  • Geotechnical advice on earthworks designs and structure foundations.
  • Participation in NRA risk workshops for the scheme and making presentations on interpreted geotechnical risks and design constraints for the proposd development including extensive soft ground, peat deposits, karst and deep cuttings in glacial till.
  • Preparation of the geotechnical section of the Preliminary Design Report for inclusion in the EIS.
  • Advice on hydrogeological design mitigation measures for the sections of the scheme through areas with protected habitats.
  • Preparation of a report on spoil management options for excess unacceptable material generated from the scheme – including peat deposition areas and lime modification or stabilisation of unacceptable glacial till.
  • Attendance at the ABP Oral Hearing on behalf of Sligo County Council.
  • Preparation of the scope of work, specification and contract documents for detailed ground investigation and assisted in the evaluation of the contract tenders and suitability assessment questionnaires.
  • Full time supervision and contract administration for the detailed SI works with a resident engineer on site and technical support from the office, including in-situ and lab test scheduling.
  • Preparation of the geotechnical interpretive report for the development of the Specimen Design