Next week's edition of RTE's new series 'Building Ireland' visits Drogheda as it has the finest railway bridge ever constructed in the country, the Boyne Viaduct. Also featuring on Tuesday's programme is the Mary McAleese Boyne Valley Bridge.
Engineer Tim Joyce investigates the construction of the Boyne Viaduct at Drogheda and its reputation as one of Ireland's greatest examples of Victorian industrial engineering. Architect Orla Murphy discovers the design of a 21st century bridge over the Boyne and Geographer Susan Hegarty explores 8,000 years of human settlement in the area.
“The Boyne Viaduct is one of Ireland's most ambitious examples of Victorian industrial engineering. And one of the great adventures of building ireland,” says engineer Tim Joyce, presenter on Building Ireland.
Drogheda's iconic Viaduct was built nearly 160 years ago to link by rail the two largest cities on this island: the administrative capital Dublin and the industrial capital Belfast. In doing so a way had to be found to bridge the 540 metre span of the Boyne Valley at Drogheda. Constructing a railway viaduct in iron and stone on this scale was full of problems and controversies. Nothing like it anywhere had ever been attempted. But on completion it was considered the engineering marvel of the age.
The project faced challenges of an immense scale from day one and there were powerful forces at work on site as local historian Brenden Matthews highlights in the programme.
“Sir John McNeill who was the great engineer of the day, a native of Dundalk in County Louth. He’d seen ideas. There had been many bridges of similar construction especially in America built of wood, there had been five or six other bridges built across the world and this was the 7th bridge of its type to be constructed. And then of course there was the contractor William Evans from Bristol, who actually undertook the construction of the bridge itself.”
William Evans began to construct his soaring stone arches on the north side of the river. Working inwards from the riverbank towards the embankments his scaffolding dominated the landscape overshadowing the town. Just two free standing stone piers in the riverbed would be needed to lay the way for the iron superstructure.
The best and brightest Irish engineers of the day were associated with the project and their correspondence in the archives of Drogheda Harbour Commissioners, details their expert opinions - and disagreements as Tim Joyce finds out in the programme.
Famous railway engineer William Dargan guided the route and Bindon Blood Stoney pioneered the testing of iron for the bridge. In terms of its scale and complexity, the construction of the Boyne viaduct was a showpiece of Victorian engineering. But a year into the build, it was running behind schedule, faced technical problems and industrial disputes. It was all bad news for the building contractor, William Evans as Brenden Matthews explains.
“Evans began this work in 1852 and by early 1853 he had already got the arches done on the north side and at the same time he had his men working in the river constructing the two piers 13 and 14.”
But these free-standing piers had to be built on solid bedrock. Inside a cofferdam, the workers kept digging down through the mud and silt of the riverbed – 20, 30, 40 feet down and still no luck.
Brendan Matthews contunues, “boreholes had been done prior to the construction of the bridge and it was thought that they would hit solid ground beneath the bed of the river at this point. But unfortunately for Evans it didn't work out.”
To add to his problems, a storm on Christmas Day 1852 brought two cranes crashing down into the Boyne. Evans couldn’t sustain the financial pressure and he was declared bankrupt. Despite the series of disasters, Evans committed to stay with the project until foundations for the pier were reached. And the digging continued. So just how did they finish this structure?
Bridging the Boyne has always been a design challenge as Architect Orla Murphy is discovering with rare access inside the Mary McAleese Boyne Valley Bridge.A familiar landmark on the Dublin-Belfast route the inverted Y central pylon and the cable stay design is very contemporary, simple and elegant.
Murphy highlights how “The single pylon gives it a light structural form with minimal interference to the protected and sensitive landscape below. But to achieve this deft architectural balance between form and function, complicated structures and materials support this bridge.”
The Boyne Valley we know was created recently - in geological terms accroding to geographer Susan Hegarty. During the last ice age massive sheets of ice scrapped along flattening the land and depositing debris. As the ice recedes, the meltwater forms channels – like the river Boyne.
“Around 15,000 years ago at the end of the last glaciation, the river Boyne was carrying the meltwater from the ice-sheets of all the midlands of Ireland. You’ve got to imagine a river flowing through here that was probably the size of the amazon, if not bigger.” says Hegarty.
According to Hegarty, “the result was a glaciated valley, an open landscape with a river, fertile soil, and forest on the upland areas at the edge. The Boyne Valley was perfect territory for Ireland’s early farmer-settlers and their constructions are important achievements of European civilisation.”
In the early 1930s it was realised that a few modifications to strengthen the Viaduct wouldn’t be enough for the demands of the 20th century. Complete reconstruction would be necessary. And the engineers now had steel to work with. New designs were prepared and once again, work began constructing the long metal spans. Nine months were allocated to the rebirth of the Viaduct in steel and the removal of the old wrought iron structure.
During refurbishment they avoided disruption to the rail service with a really clever engineering solution as Tim Joyce explains, “the new steel structure was built inside the original iron frame, leaving the bridge intact. This brilliant idea allowed trains to continue running throughout the renewal process. The frame of the section grew out from the top of the piers reaching out using the engineer’s technique of the cantilever - a bridge building technique still in use today.”
Big engineering projects of the 21st century or of the industrial age are very special markers of human achievement in our landscape. Tim Joyce highlights how “Ireland just doesn’t have as many big engineering projects as other European countries for practical as well as economic reasons. There just aren’t that many mountain ranges to bore through or valleys to cross between our large population centres. But that is all the more reason to treasure it. The engineers of the Boyne Viaduct didn’t design this bridge just for their day but for future generations like us.”
Tuesday 5th August 7pm RTE One