Concrete is at the heart of the repairs to the Great Western Railway at Dawlish in Devon after the devastation caused by last month’s floods.
The South Devon Railway from Exeter to Plymouth opened in 1846, a year late, partly due to damage to the sea walls near Dawlish, according to Brunel biographer Derrick Beckett.
Between Dawlish Warren and Teignmouth, Brunel opted for a coast-hugging route to avoid steep gradients inland that he couldn’t tunnel through due to restrictions on costs.
This 4km stretch of railway, while becoming famous for the scenic journeys it offers on a clear day, has suffered regularly from the power of the seas ever since.
A major breach of the sea walls occurred as recently as 1996, but local residents and engineers believe the effects of the storms of February this year to be the biggest ever seen.
“I’ve checked back through the records and can’t find any mention of damage and disruption on this scale, certainly since the Victorian era,” says Network Rail south west customer service manager Tim Maddocks.
We do get the occasional small breaches of the walls here, but not like this
Network Rail and train operator First Great Western (FGW) have a strategy for coping with heavy seas, involving making use of advice from forecast service provider Mouchel and adjusting or halting services accordingly. When spray is likely, FGW switches to rolling stock that copes better with salt, says Maddocks.
Site agent Lee Davey from Network Rail’s contractor Dyer & Butler has worked on this stretch of line for a number of years. “We do get the occasional small breaches of the walls here, but not like this,” he says.
The last train of 5 February had already left Dawlish when the storm of that night hit. By the next morning, an 80m long gap in the sea wall and railway trackbed could be seen, with the tracks hanging over a scar exposed right up to the doors of properties on Riviera Terrace.
The immediate job for Network Rail’s contractors first on the scene was to cut and lift out the damaged track and to support the communication cables that use the rail corridor; as well as rail signalling cable, the Global Crossing Cable laid across the Atlantic sea bed between the United States and London which also depends on this rail route.
At the next low tide, the scar was sealed against further wave damage with a covering of sprayed concrete.
A temporary breakwater was also built from a line of 11 steel shipping containers filled with rock and dropped onto the sea wall’s low-level stone walkway still intact in front of the breach.
Network Rail and contractor Amco then got on with the permanent repairs. Working around the tides, the plan was to clear the main hole of debris and backfill it with mass concrete against a permanent shutter of a wall of precast concrete vehicle barriers.
By 14 February, these concrete blocks had been delivered, a scaffold was erected for pulling and supporting new cables, and the formation was trimmed and ready for the first concrete pour. Then an even bigger storm blew in.
On the morning of 15 February we had 256m of main sea wall damaged, from whole areas missing to cracking and voiding. We also had 525m of parapet wall gone
“This one was really big. We were in a meeting at our site compound when we heard the sound of the waves hitting the station and decided to take refuge a bit further inland,” says Network Rail senior construction manager Alex Evason.
The temporary breakwater held during that night’s storm, but the containers were distorted and dislodged, and a further 25m of the sea wall was taken out. With it went much of the formation formed over the previous days.
Furthermore, the damage to the sea wall and its parapets was now not just limited to the section north of Dawlish station, but ran all the way from Dawlish Warren south to Teignmouth, 6km further south.
“The main breach at Dawlish is obviously by far the most dramatic damage and so has grabbed all of the headlines. But there is more to what we’re now up against here than just the Dawlish site,” says Network Rail project manager Tom Kirkham.
“On the morning of 15 February we had 256m of main sea wall damaged, from whole areas missing to cracking and voiding. We also had 525m of parapet wall gone,” he adds.
“While they may just look cosmetic to some, these walls are critical because, if they go, the ballast gets washed out, so they are absolutely critical to the first trains coming through.”
All of the defects have been classified to a red, amber, green system according to how critical they are for getting the railway open again. Parapets are a red item. Whereas small local failures are usually repaired with granite, contractors are now reinstating the walls with insitu concrete tied into the foundations with drilled and grouted steel dowel bars.
Plymouth-based manufacturer Pipex is providing shuttering to create a stone wall finish.
Another cause for concern is the access ramps down to the beach, which Kirkham says are “just as important” as other structures on the railway.
“This is the only way we can get down to the beach to repair the main walls,” he explains. “The ramp at Teignmouth has to be repaired before we can get access to carry out repairs at Smugglers Lane.”
Another issue for Network Rail to deal with is the 32 separate failures in the red sandstone cliffs between Teignmouth and Dawlish, which are thought to have been caused by groundwater from above rather than the action of the waves.
Although the waves did reach the cliffs, the localised failures are characterised by new watercourses appearing from the cliffs at these points.
The tracks north of Teignmouth are already protected by 3m high aluminium post and wire mesh fencing, due to the susceptibility of these cliffs to failure.
Nonetheless, the fences have to be taken down, the spoil from the failures removed by rail mounted machines, the failures assessed and remediated and the new watercourses rerouted through existing culverts in the main walls.
“We already had rope access contractor Can working in the area, which was fortunate. Can teams will be remediating the slope failures with soil nailing where necessary,” says Kirkham.
The other main contractors involved are Bam Nuttall, Sisk, Amco and Dyer & Butler, and Network Rail’s designer on the project is Tony Gee. Local labour has been provided by Teignmouth Marine Services.
At the main breach at Dawlish, Amco reinstated and extended the line of rock-filled shipping containers and has now filled the hole with 5,000m3 of mass concrete to a depth of 3m.
The concrete is being pumped distances up to 160m, with two static pumps supplied by Professional Concrete Pumping transferring the concrete down from Teignmouth Hill Road above the station to a mobile pump on Riviera Terrace.
The mass concrete was brought up in four lifts to a benched and tessellated pattern to avoid forming shear planes and lines of weakness, says Kirkham. A reinforced concrete strip footing has now been poured on the rear of the mass concrete formation.
Two rows of bespoke precast concrete L-shaped units will be placed next - a rear row on the strip footing and a front row straight onto the mass concrete - to form a track bed channel. This will be filled with track ballast while forming a 2m high parapet wall on the seaward side and a 3m high retaining wall, which will be backfilled to reinstate Riviera Terrace behind.
Prior to 14 February, Network Rail and transport secretary Patrick McLoughlin were promising a resumption of rail services within six weeks of the initial breach at Dawlish.
The aim is to get the line between Exeter St Davids and Plymouth reopened by Easter, although Network Rail chief executive Mark Carne is seeking an earlier opening.