Getting wet on the beach – sounds like a happy recollection of Things We Did Last Summer. Countless songs and movies tell us that sun, sea and sand is the way if you’re California Dreamin’ or just Surfin’ USA. However, for most of the year, in this country we approach the water with more caution – even at the height of summer, in a wetsuit, it can be a case of Don’t Go Near the Water. And we have royal precedent for this caution. In 1216, King John showed that you Can’t Wait Too Long when he lost the crown jewels to the incoming tide in the Wash. Two centuries earlier, King Canute played and lost at Don’t Back Down when he famously commanded the tide to halt. It didn’t.
So why, in late February, should a bunch of engineers choose to transport a bridge deck the best part of a mile along St Bees’ beach in Cumbria, at a speed slower than King John’s baggage wagons? No, this wasn’t some bizarre charity event, a pontist equivalent of the Dakar Rally.
Neither did someone wake up one morning and think, “Wouldn’t It Be Nice…?” This was in fact the fully risk-assessed, preferred construction method for Underbridge 178, part of the £1.7 million Package 604 of six deck replacements being undertaken by BAM Nuttall on behalf of Network Rail.
The Nearest Faraway Place
Rhiannon Price, scheme project manager for Network Rail, explained: “The Cumbrian coastline is very scenic but remote. Here, the railway runs through the dunes beside the beach. There is very limited access.” The bridge crosses Sea Mill Lane in a single 2675mm span with 4400mm overall width carrying a single bi- directional line.
“Construction access along this narrow lane was not an option,” Rhiannon explained. The lane leads to a few houses huddled on the sea-front, blessed with an impressive view when the Surf’s Up.
Richard Atkins, project manager for BAM Nuttall, added: “We initially looked at using a Kirow rail-crane. Then one of our engineers suggested using the beach. Over the last thirteen years or so we’ve had a lot of involvement with sea-defence projects all along the Cumbrian coast. We’ve previously used 35 tonne dumpers and 40 tonne excavators along the beach, and transported rock armour in four or five tonne lumps. But we’ve never needed to take anything quite this large.” The deck was precast in a single 31 tonne reinforced concrete unit by Shay Murtagh.
Mark Billington, project engineer for Network Rail, added: “The advantage to us was that the method removed risk from the railway possession. The deck move was planned for the week before the possession so it would be ready and waiting. Removing the rail crane from the equation simplified the possession work.”
When the time came, that preparatory work passed smoothly and ahead of schedule. It included removal of the old bridge, break- down of the abutments to level and installation of the new deck. Reinstallation of the track by Story Rail completed the job, with a 230mm track lift to suit the increased 275mm construction depth of the new deck and minimum 200mm ballast below sleepers, compared with the former steel-trough and longitudinal timber arrangement.
Richard Atkins confirmed: “The beach was not such a scary method for BAM Nuttall. We had a good understanding of the risks involved from our previous coast protection work.” Working between tides is the obvious challenge – you could say It’s About Time. “But the tide also causes the terrain of the beach to change on a daily basis”.
Take A Load Off Your Feet
Regular readers of The Rail Engineer will have followed the adventures of ALE’s self propelled modular transporters in previous episodes. “I Get Around” is perhaps becoming a motto. The transporters have independently controllable axles and are sized to distribute the load evenly. However, this move was a Break Away from previous experience.
“We carried out plate bearing tests and checked how the sand performed at different tide levels”, says Richard Atkins. “The results showed that the sand was typically harder than the adjacent public
car park where we set up our compound”.
“Don’t Worry Baby” isn’t the typical response you get from a temporary works department. Soft spots and liquefaction of the sand under the transporter remained a concern – on the beach, there are no such things as Good Vibrations. However, there was limited value in carrying out further testing, given the twice-daily change of the beach with every tide.
“We planned to use trackway mats to distribute the load further”, said Richard Atkins. “And we also had a winch wagon on standby to pull out the transporter for the worst case of it becoming stuck. The biggest risk to us was using up valuable time”.
19 February 2013 was chosen for its neap tide. This gave the smallest tidal range and most importantly, the lowest high tide, maximising the available time on the beach. High tide occurred at 05:33 with a level of 6.00 metres. Low tide was due at 12:07 with the water dropping to 2.70 metres. By 18:17 the sea would be back up the beach at 5.90 metres.
“We allowed eight hours for the move”, explained Richard Atkins. The Fun, Fun, Fun began immediately with an inch-tight squeeze past the RNLI lifeboat station and down the lifeboat slipway onto the beach.
At 07:30 the message was passed to the lifeboat crew: “Sail On Sailor”. They launched their Sloop John B, ready to respond rapidly to any required rescues. Richard Atkins explained: “The lifeboat has to respond within minutes to any callout – and our equipment on the slipway would have prevented this. We had lots of discussions with the RNLI and agreed the critical few hours when they needed to be at sea to maintain their response times.” The boat, an inshore Atlantic 85, has been called out five times in the last six months.
By 08:00 the way was clear for the transporter to leave the car-park and descend the slipway onto the beach. “We had 1450 metres to travel. We had calculated how far we had to go each minute. The team reviewed progress every 50 metres of the move. At times we were making twice the progress we needed”.
Here She Comes
Top speed of the transporter was a moderate walking pace – no Little Deuce Coupe here. But the rate of progress was mainly determined by laying out the mats, provided and placed by Eve Trackway. Up to 12 mats were set out at a time. Once the transporter had passed over them the mats were collected and leapfrogged to the front again.
The general line of route was chosen in advance. Initially it needed to steer offshore around six beach groynes. Further along it had to avoid the SSSI-listed cliffs. God Only Knows there were many other constraints, including the presence of protected species and old structures for collecting mussels. Then there were the beach features including rivers draining the beach, shingle and boulder fields.
However, it was always recognised that the optimum route would have to be chosen on the day, a real Surfin’ Safari. Indeed, just a few days before, bad weather had significantly changed the terrain of the beach. The route was reassessed by the team, including the ALE engineers and the environmental consultant Ian Hassle. Ranging poles were used to mark the route.
All the beach works were covered by a license with the new regulatory body, the Marine Management Organisation. The license also specified the environmental controls. “We supplied a 4×4 vehicle equipped with spill kits, first aid boxes, the ranging rods and all the other environmental and safety gear we needed”, Richard Atkins commented.
With the whole beach as a worksite, unusual measures had to be taken for safety. Clearly the beach could not be shut. “Our approach was to have plenty of staff on site”, Richard Atkins added. “They were extensively briefed and were on hand to keep the public away from our activities”. Nevertheless, the circumstances gave a rare orchestration of construction accompanied by Pet Sounds, as the locals walked their dogs, Wendy, Peggy Sue and Barbara Ann.
I Can Hear Music
11:30 was the go – no go decision point, otherwise known as the point of no return. After this, there is no use screaming, Help Me Rhonda. Progress had been good so the team pushed on. Rhiannon Price added: “There was a lay-down point beyond this above the high-water mark, about two-thirds of the way through the journey. If need be, we could park the bridge overnight and carry on the next day”.
The going became harder beyond this point. To reduce the risk of going closer to low water level, a passage had been found through a boulder field. However, this took more work, as a temporary bridge was constructed over the boulders using the mats, with pipes installed below to avoid disrupting the water flow.
Finally, at 16:30, the transporter gained the high water mark and left the beach, almost exactly at the planned time. Meanwhile, the last of The Warmth of the Sun was ebbing away. Kiss Me Baby, said the sun to the sea, as the west-facing coast produced a perfect pink-tinged sunset to end the day.
It’s Over Now
The earliest record of King Canute’s exploits is given by twelfth-century chronicler Henry of Huntingdon.
His account gives clues that King Canute knew that the tide would come in regardless of his command, that in effect he was conducting an early publicity stunt. It served to demonstrate the limits of his power – but also the extent of his wisdom and knowledge in recognising and understanding these limits.
In a modern take on this, Richard Atkins expanded on how the limits of power and control were acknowledged by the project: “Planning was key. We planned for every failure, the small things as well as the big things. And because of this, in planning for success by planning against failure, we did succeed”.
Richard Atkins paid tribute to everyone involved: “The site team really pulled together to make this a success. It doesn’t matter how much planning has happened, it is the effort and determination of the workforce on the day which pulls off a project like this.”