Most underpasses are high enough for cows and a farm jeep to pass through. This article from the Farmers Journal features a road underpass which is high enough for a mid-size tractor to drive through.

It is on the farm of Tom and Ashley O’Halloran of West Court, Callan, Co Kilkenny and it has just been built for them by Croom Concrete. Being able to drive a tractor through a tunnel has advantages, especially where the road is very busy. It reduces the risk of a traffic accident. Not opening road gates reduces the risk of stock getting out on to the public road. It can save time as it tends to be a direct route.

The Callan to Cashel Road

Tom O’Halloran needed an underpass because half of his land is across the busy
Callan to Cashel road (R695) and his crossing point here is on a bad, blind bend. He went for a high one to give him safe, easy access for routine jobs such as bringing feed out to calves, spreading fertilizer, top, etc. He got drawings done up, obtained planning permission and called in Croom Concrete to construct the tunnel.

Underpass Box Culverts

The typical underpass uses box culverts that are 2.1m (seven feet) high, internally.
The culverts here are 2.5m (eight feet) high. This, and the presence of water mains, meant the excavation for the underpass was approximately 4m (13 feet) under the road surface. Thankfully, it proceeded without meeting rock. Only when it came to digging out for the rainwater sump did the machine hit bedrock. Big culverts are heavy – these weighed 13t each and required a 100t crane to lift them.

This job was relatively straightforward. There were no optic cables or gas pipes.
There was one water mains pipe. The RSJ beam was used to support the pipe and shield it from damage during the digging out or back-filling.

It frequently happens that the easiest site for an underpass is very close to the farmyard and this can restrict space, particularly for the approach route from the yard. The site here has no such problems. It’s about 200m from the yard and there is plenty of room to make a gradual slope down to the tunnel — there are no buildings, silage pits or yards in the way. The surrounding ground is quite level. The approaches to the tunnel are over 90 feet long which, in turn, makes the climb gentle and easier on cows’ feet. The soil banks are neatly battened down by the excavator and will be stable. The other point that jumps out here is how dry the site is. The work was done this month. Clearly, the ground here is very free draining. We can see just how deep the cut under the road is for this tunnel. The banks above the approaches have now been fenced off for safety. There is a wall and soil bank on top of the tunnel. Presumably, because of the bends on this road the county council required Tom to also erect crash barrier on the road edge, on both sides.

 Precast Bunker Building Blocks

At 4m, this tunnel is wide as well as high. Tom O’Halloran told me he now uses farm roads that are 6m wide and he didn’t want bunching and slowing down at the tunnel. Croom Concrete use these precast bunker building blocks to construct the side and top. The main benefit is that once the blocks are dropped in place soil, etc, can be back-filled around them and the work crew can keep going. There is no going home while allowing concrete to set. The blocks are 1,400mm by 700mm by 700mm and interlock for stability.

Despite the depth of this culvert, Tom O’Halloran was keen to let any rainwater flow away by gravity rather than use a tank and pump. Gravity flow is simpler in the long run and, in any case, the site is a long way from the nearest electric point.
Thankfully, he was able to do so. The collecting sump seen here has a capacity of 450
litres. The floor of the underpass has now been concreted along with a 5m external apron at each end. This concrete floor slab slopes into the collecting sump.

 The Result

With the land falling away from this end of the field Croom were able to run a pipe from the sump to a ditch 250m away at the bottom of this field. For the first 100m or so of high ground, the pipe is buried at over 4m deep.

Tom O’Halloran expects that the new underpass will save him about one hour of work per day and will make his day to day work safer. ‘‘Hopefully, the cows will rise in milk yield too, as they won’t be waiting around.’’

(Mooney, P. (2012). Road underpass high enough for a tractor. The Farmers Journal, 22nd September 2012, p.42 – p.43) – From the