Anaholty Bog Remedial Works N7 Contract

The Anaholty Bog N7 Section Contract works included remedial action to a pile-supported embankment through a section of the M7 motorway located across from the Annaholty bog, with up to 30m of peat and underlying yielding ground. The works commenced in the last week of June 2010 and completed by the last week of August 2010, to ensure the opening of the final section of the M7 project to the public by the October deadline. Prior to the commencement of the MEIC contract, a number of the piles supporting the embankment through the peat bog section had failed in isolated locations on the outside edge of the embankment, thus increasing the load on the remaining inside piles. The key objective of the remedial works was to rectify the failed piles, and put in place measures to ensure that the remaining embankment and piles were secure. Bothar Hibernian, in conjunction with Hyder and MEIC developed the following design and methodology for completion of the works;

  • Firstly, Benefill material was pumped into the voids that existed below the Annaholty Bog section of the M7 motorway. This process assisted in supporting the piles and pilecaps that were exposed during the remainder of the remedial works.
  • Next careful removal of the existing road surfacing, services, fill and the geotextile load transfer mattress to expose the underlying pilecaps.
  • The exposed pilecaps were surveyed for evidence of collapse and all failed piles and pilecaps were removed and remedial works carried out.
  • The Works were completed via a temporary platform that was positioned adjacent to the site. This platform was constructed with lightweight fill in the form of tyre bales, Stablinka geotextile and processed stone fill. This temporary piling platform had to be robust enough to support cranage, concrete pumps, excavators and an 80tonne piling rig. In addition to this, the platform had to be resistant enough to avoid the transfer of the working load to the working area, which could potentially have serious consequences and exacerbate the issues already affecting the carriageway. This temporary platform was constructed in conjunction with the removal of the existing road surface to pilecap level, to allow for the economic reuse of material, while also ascertaining the extent of the damage to the existing piles in the process. This process ensured that the temporary works platform was tailored to suit the remedial works required.
  • The failed piles and pilecaps were removed using specialised equipment without disturbing the adjacent piles.
  • Replacement piles were then installed and tested, along with a number of the existing piles, to ensure that the road could safely accommodate the loads required.
  • This section was then covered with a 400mm RC slab, which was poured in 3 pours of approximately 350m3 each, extending to over a 100m in length and 28m wide.
  • Finally, the 400mm RC slab was waterproofed and cured. The motorway section was then finished with services, road surfacing, central concrete barrier and other associated works to return the road to the required standard.

All works were completed on program and on budget, and the difficulties associated with constructing in these very challenging conditions were overcome, allowing the motorway to function to the standards required.

Client

Bothar Hibernian

Client Representatives

Hyder Consulting Engineers

Date

June 2010 – August 2010

Contract Value

? 1 100 000

Location

Anaholty Bog, Nenagh, Co Tipperary

Date

January 22, 2021