Underpass enables expansion

In April, a large underpass was constructed on the well-known Browne family farm in Killeagh, Co Cork. The underpass now gives easy access from their main grazing block to an outfarm across a road for their large dairy herd.

It was constructed using precast concrete culverts supplied by Corbett in Tipperary. John Mulcahy from Mulcahy Steel Ltd, the local building contractor, organised the installation.

Organising the installation of the underpass took far more time than the installation itself because procedures had to be followed.

First of all, the Brownes had to get planning permission from Cork County Council for the development – Grasstec helped them plan this. The building contractor – John Mulcahy – had to be registered with the county council as the main contractor for the site and an application for a road opening licence was granted.

The road opening licence allows a registered and insured building contractor to carry out work on a public road. A member of Mulcahy’s staff had completed a signing, lighting and guarding at roadworks course already and a traffic management plan was agreed with a local engineer from the council.

The dates outlining the planned closure of the road had to be advertised twice in the local paper five weeks before work could commence to give adequate notice to locals of the road closure. Once all this work was complete, the county council gave the go-ahead for work to commence on the planned dates. Excavation work started on a holiday Monday and the public road was reopened to traffic by lunch time Thursday.

Picture one

John Mulcahy said the site for the development was ideal because there was a fall on one side lower than the depth of the underpass, which allowed rainwater to be drained away easily.

This meant there was no need for an effluent tank or pump to deal with rainwater.

A digger contractor excavated the site to a depth of 3.4m. Mostly gravel and loose stone came up during the excavation and this was used in the construction of other roadways on the farm.

A 6in service pipe was laid in the foundations of the underpass that would allow water and a link wire for the electric fence to cross the road from the main block to the outfarm easily.

Once the site was excavated, the base where the culverts were to be positioned was rolled with a 3.5t vibrating roller. Next, approximately 50mm of 8mm- (maximum size of stone 8mm down to dust) was laid and levelled by laser. This layer wasn’t rolled because the culverts sit into the sand and are adjusted as they are locked into each other.

Picture two and three

A 130t crane was used to lift the 12 concrete culverts (each culvert weighs 11.5t) into position. The culverts were laid back-to-back, creating two passageways.

Each culvert is 3m wide, 2.1m high (internal dimensions) and they come in 1.5m sections. They cost about €1,875 excluding VAT. 1,200-gauge plastic sheeting was laid on the top of the culverts to prevent water dripping inside.

Precast concrete walls were placed on top of the culverts so that traffic can cross the underpass safely. The precast concrete walls are 5m long and 2.1m high.

A layer of 8mm/minus was put on top of the plastic to protect it and 600mm of 4in down was laid on top and compacted with a vibrating roller.

Approximately 50mm of 10mm hot-chip tar was laid, raked by hand and rolled to leave a smooth finish for traffic. When the new road surface was complete, 1.5m of the side walls was visible.

Picture four and five

The roadways leading to and from the underpass were prepared before work started, which meant once the culverts were laid, it was more or less ready to take cows.

Simon Browne says that woodchip is being laid on roads now because it is easy on cows’ feet and prevents stones from getting trapped in their hooves. He says woodchip works well once water is not sitting on the road.

He plans to do all the roadways with woodchip once repair work is done on more of the high-traffic areas.

Four precast walls were erected at the end of the culverts to prevent the clay banks from slipping. Steel hooks in the concrete retaining walls allowed the electric fence to be strained from the wall itself.

Cost

To buy and lay the concrete culverts and retaining walls, it cost approximately €44,000 excluding VAT. This does not include excavation because other roadway work was done that was not itemised. Planning permission cost approximately €2,000. Simon said the cost would be reduced significantly if just one row of culverts was laid rather than two. However, he does not regret laying two because large numbers (400 to 550) of cows go through the underpass. He is very happy with the work and the finished product, which opens up a grazing block of 100 acres and possibly another 40 acres by walking cows to two fields further on.

“We couldn’t expand numbers without the underpass and you wouldn’t be able to cross 400 cows on the road twice a day,” he explained.