Monaincha Wind Farm, Offaly

Project outline

With an ever increasing need for renewable energy, planning permission was granted for a large wind farm just outside Roscrea, Co. Offaly. The wind farm featured the largest ever turbines in Ireland, in 2013, each stretching 91m to the hub. A specialist team from Murphy was tasked with securing 12 turbines to this boggy terrain, to ensure the ultimate success of the project.

Murphy International Ltd constructed a ring of rock for socketed piles, to support the wind turbines. The piles were 900mm diameter and varied in length between 16.5m and 30m depending on the rock level. The number of piles in each base varied from 16 – 20.

Key challenges

The main challenge was working with the difficult and quite unique ground conditions - a layer of peat upon a layer of silt, with rock further below. In some places the peat and silt layers were up to 25m deep.

For this project to be successful, rock socketed piles were required by the client. There were no piling rigs in Ireland capable of delivering the depth necessary, apart from the Murphy-owned Bauer BG28.

A further challenge was splicing the cages and lifting them with a tandem lift. However, Murphy have a number of engineers who are certified as CPCS Appointed Persons for lifting, so along with our own safety department and supervisor, the Murphy project team came up with a safe and efficient method for lifting the long cages.

Due to the rough terrain and the remote location of the wind farm, it was necessary to install a complex series of haul roads and piling platforms, to allow access to site for the plant and machinery.

Project delivery/ innovations

The programme delivery timings were ambitious, so to meet the needs of the client, Murphy proposed and put into place key measures.

• Murphy put two rigs on the job and a very experienced crew to meet the programme targets. Murphy also put a crawler crane with each rig, to place the steel cages and pour the concrete in the piles. A second full string of casing was also bought for each rig. This meant that the piling rig could bore out the next pile while the previous pile was being concreted - effectively doubling the production.
• The Murphy Bauer BG28, the largest piling rig in Ireland, was used to install the required depth needed for the piles, 16.5m to 30m, working with the rock level.
• Murphy crawler cranes were used to place the reinforcement and the concrete - rather than the piling rig. This innovative move allowed the piling rig to drill the next pile, for ultimate efficiency.
• In addition, Murphy designed a joint in the cages, which allowed for the 30m long cages to be lifted off, in one piece. This meant that the cage was created by operatives while the pile was being drilled and speeded up the entire process, as opposed to the more traditional route of splicing the cages while being placed in to the open casing.
• Murphy International designated key people to ensure project milestones were met throughout the contract, overseeing the planning, safety, quality and environmental challenges, as well as ensuring the project ran to budget.