The new road underpass was well-wanted on Pat Sheehy’s farm at Springmount, Ballingarry, Co Limerick. Half of his 100acre grazing platform is across the Ballyea Road, which is busy mornings and evenings.

“It was costing me money,” he said. “I couldn’t bring the cows across the road in both the morning and evening – it was too difficult to manage. Therefore, I couldn’t graze on a 21-day cycle and that was affecting milk solids and profitability.”

He went to Croom Concrete and was happy to have the firm do the complete job, including obtaining planning permission and the road closure permit.

Installation took just eight days and was completed late last month in perfect weather and ground conditions.

Pat had the spoils moved off-site and used to fill in a hollow in one of his fields. “We peeled back the topsoil, filled in the hollow and then levelled the soil again.”

Pat told me that he had not expected as big a volume of spoils. “But when you think about it, the job is the same as digging out a large underground tank.”

Pat paid Croom Concrete approximately €46,000 including VAT for the underpass. He reckons that the removal of the spoils, plus some stud rail fencing around the underpass, will bring the total cost to €50,000 excluding VAT.

“The price I paid for the tunnel was actually lower than prices I was quoted a few years ago. Prices seem to have come down.”

The price of an underpass is straightforward and visible. However, the benefits it brings are more difficult to put a value on.

The obvious ones include better use of grass, reduced labour and reduced risk of an accident on the public road.

“One other thing I’ve noticed is how much cleaner the yard is. When you’ve 100 cows standing around after milking waiting to be brought across the road, your yard gets very dirty.”

Site

At the site chosen for the underpass, the road was almost 4m wide. The ground on the yard side of the road was about 2ft below the level of the road. This meant that the approach ramp into the tunnel could be relatively short.

Across the road, the ground was about 3ft higher than the road. This meant that a lot of digging out would be required.

Croom Concrete put two excavators, two dumpers, a roller, a skid steer with road brush and a mini-digger on-site.

A feature of this job was that Croom Concrete used all pre-cast structures and little concrete was poured on site.

Six box culverts were used. Pat Sheehy went for a 3m-wide tunnel. The boxes are 3m wide and 2.1m high (both internal measurements). Each box is 2m long and weighs 13.5t.

A stone base was laid in the excavation and rolled. The boxes were lowered by the crane. The gap outside the box walls was backfilled with 15N lean-mix concrete.

“The standard tunnel is now 3m,” Joe Costello of Croom Concrete told me. “We’ve done 22 this year and only two were 3.5m, all the others were 3m.”

The final culvert at the yard side is U-shaped, providing a floor and two side walls but no roof. The walls are 2.7m high at the end next to the tunnel but slope down to 1.2m high at the front.

Built into the floor is a grid cover for the precast 2,000-gallon underground tank placed at the end of the tunnel to catch effluent.

At the other end of the tunnel, where the ground is rising, precast wall panels were used on the left and right to make the side walls.

I-beam stanchions (10inx8in) were concreted into the ground and the panels slid down into the pillar web from above.

Reinforced

The panels are 150mm thick and are reinforced with pre-stressed reinforcing bar. The wall is made with two 1.5m-high panels so it’s 3m high in all. Ten panels were used of varying length: 6m, 3.5m and 3m.

Overhead, the safety walls at the side of the road were precast. These are L-shaped and sit on top of the box culverts.

The bottom part holds in the stone material under the road surface, preventing it from being pushed out to the sides.

The top part of the structure rises at least 1.2m above the road surface as a safety wall to prevent a vehicle skidding off the road and down onto the underpass.

The bottom of these units are 3.5m long – to fit down on the 3m box culvert. The top safety walls are 5.4m long to replace the length of bank and hedge that is cut out when excavating.

Joe Costello of Croom Concrete told me that the benefit of using precast structures is speed of work on-site.

This in turn helps to keep costs and the price to the farmer down.

“This way, the crane lowers the culverts and then lowers the side walls at the tunnel ends and the safety wall at both sides of the road.

“Precast structures can be backfilled immediately. The road can be reopened that evening and is safe for the public to use.

“If end walls had to be shuttered, then the soil bank would have had to be angled back for safety reasons. This would have added to both time and cost of reinstatement.

“Shuttered walls would then have to be left to harden before being backfilled.”

When finished, the crew placed a shallow screed of concrete on the floor of the tunnel. “This seals the floor, directs the effluent to the tank and gives grip.”

Another benefit of using precast structures is that final cost is more predictable for everyone, including the farmer.

Croom Concrete has received a number of orders to supply its box culverts and precast wall units to farmers in the UK.

“We’re doing one next week. He can’t get structures like that over there. And he’s happy that he knows the cost in advance.”