Gas Main Protection Works
A major GNI (Gas Networks Ireland) main, servicing the numerous industries in Little Island, passes through the Dunkettle worksite, with a number of the new road links that make up the Interchange Upgrade to be constructed on raised embankments directly over the gas main. It is critical that the gas main be maintained and protected prior to the road construction works proceeding.
The works involved the confirmation of the position of the gas main, followed by the installation of 450mm diameter ‘Continuous Flight Augered’ piles two metres offset from the gas main. The piles were then broken down to the required level and tested. A capping beam was cast on top of each of the rows of piles running parallel to the Gas Main. Precast concrete slabs were then placed on top of the capping beam which will provide protection to the gas main and allow access if required at any stage in the future.
Gas Main protection works.
Various Utility Diversions
A key objective of the Advance Works completed during 2020 was to divert the majority of the existing underground and overhead services which clashed with the proposed works so that these complex works elements are already in place ahead of the main contract works starting.
This involved significant ongoing liaison with all of the relevant stakeholders to initially identify the interfaces and thereafter agree how best to incorporate the services in the proposed future road layout. A collaborative approach was applied and each of the service providers were given details of the proposed works and they individually assessed the possible impact of the same on the works.
Once the required scope of work was agreed, the works were completed in order to allow the services to be diverted. This involved the installation of ducting in offline areas by day and numerous road crossings were also undertaken by night across the N25, the R623 Little Island Regional road, and the main Dunkettle Interchange Roundabout so that disruption to traffic was minimised. The works included in the advance works included the following:
- 5nr. ESB diversions.
- 4nr. Eircom Diversions.
- 4nr. Comms Diversions (Enet & Viatel).
900mm Irish Water Trunk main
The section of 900mm water main which passes through the site forms part of Irish Waters/ Cork County Councils key infrastructure which provide an essential water supply to the industries and residents in the Little Island area. The main itself which carried 13,000 L/min (7.5 Olympic Swimming pools per day) was initially installed in the early 1970’s and needed to be replaced to accommodate the construction of the various new Dunkettle Interchange link roads and structures over the watermain.
Due to poor ground conditions, extensive ground improvement works were required, including; piling, and excavation/replacement of existing ground in advance of the main installation. These ground improvement works were to ensure that any settlement would not impact the main once the road embankments were completed.
Extensive planning was required in advance of shutting down the existing watermain. Alternative supply arrangements were put in place to ensure service was not disrupted during the shut-down period. The main was taken out of service on the 26th May 2020 with a programme duration of 18 weeks. The replacement main consisted of 255 metres of welded steel pipes with a diameter of 900mm.
In order to accommodate a proposed structure on the line of the main, along with a change in ground levels a vertical drop of circa 5m was incorporated into the design. Due to location of this vertical drop being in close proximity to the N25 off slip a caisson shaft was constructed as a temporary works solution so as minimise any disruption to traffic. The main was commissioned and taken back into service on the 29th September 2020 in line with the initial programme, allowing for the 7 week site shutdown due to Covid-19.
900 mm Water Trunk Main