World Of Water
10 Feb 2005
Winchester Cathedral Underpinning
I don’t watch much television, says Colin Wheeler, but Sunday evening, 17th January at 7pm on BBC2 was a memorable exception! ‘Flood at Winchester-saving the great building’ was both interesting and timely.
Basically the Cathedral building was originally and inadequately founded on a mattress of crossed tree trunks on peat above a layer of gravel, which had the necessary carrying capacity. As a civil engineer I was pleased to see that 100 years ago the architect called in consultant engineer Francis Fox to investigate the foundations, when structural cracking and settlement threatened the future of the Cathedral.
The fund raising, and escalating costs, sadly emphasised that some things have not changed! There was also commendable recognition of the efforts of the diver William Walker who, using the most primitive of diving suits, underpinned the Cathedral, single-handed, over a period of six years.
At least the helmets are lighter!
I recall the incidents, which led British Railways Board’s Chief Civil Engineer to instruct that diving inspections should be undertaken to check the foundations of bridges over water. Foremost in this work today are Bridgeway Consulting.
The origins of their specialist diving teams go back to 1963 when Scuba diving had replaced the old heavy diving suits fed by umbilical air supplies. Now, due to changing views on safety, the use of air from the surface and full voice communication to divers wearing hard helmets has returned, but at least the helmets are lighter, being made of fibreglass!
Diving and underwater inspections
Contracts for ten years of structures examination work were let on a geographical basis back in 2003. But specialist companies, who are Network Rail accredited via the Link-Up accreditation system and regularly audited on their competence, provide ‘diving and underwater inspections’.
Additionally the divers themselves must be accredited competent in accordance with RT/CE/S/047 unit 8, which is the unit dealing with bridge examinations under water. Bridgeway regularly provide this service to examination specialists such as W.S. Atkins in the south, Mouchel/ Parkman in the Midlands and North West and Owen Williams in the North East, East Anglia and part of the Great Western area.
The January floods
Every year diving inspections are carried out to confirm the integrity of foundations, submerged piers and abutments etc. A diving team consists of a diving supervisor, a diver, a standby diver and an attendant. All but the attendants are qualified divers.
The work cannot be described as glamorous. Working in wet confined spaces and ‘mucky places’ predominates, or as one of the divers put it to me, ‘we go where the regular examiners refuse to go.’ In fast flowing rivers visibility is often very low and examinations rely on feel and probing with rods. But the January floods provided some unscheduled work this year, often in uncomfortable and potentially hazardous locations.
Blaenau Ffestiniog to Carlisle
The first call came during the first working week after New Year. Bridgeway Consulting agreed to be on ‘stand by’ for Llandudno Junction and the Blaenau Ffestiniog Branch from Friday 7th January. The branch was already closed due to the floods. But it is neither safe nor practical to attempt diving examinations until the water goes down.
A team was assembled ready on Sunday January 9th and were waiting for the water to recede. But then Carlisle became the priority, with the West Coast Main Line north of Carlisle closed. By Tuesday January 11th the water had receded sufficiently for the team to dive under bridges 3 and 3A, which are just north of Carlisle station.
Bridge 3 is supported on stone piers in the riverbed whilst 3A is on circular stone column supports. Single line working for freight trains through to Kingsmoor Yard Depot was permitted before completion of the inspections. But the water had risen onto the deck and some ballast had been washed away from the track.
Agreement with Network Rail’s Engineer on site
Neither bridge had been damaged; the structures down to riverbed level were examined and revealed no loss of material from the riverbed. The team then moved on to bridges 5 and 5A, which are half a mile further north. This was a different situation. Nuttalls and WA Developments were already hard at work repairing the embankment, which had been partially washed away.
These bridges are supported partly on stone piers and partly on concrete columns. A full examination of the central pier could not safely be attempted due to the strong river flow; the river was still in flood. But the recorded scour risk assessment indicated that 3 and 3A were the greater risk. Following the partial examination, Bridgeway were able to reach a soundly based technical agreement on these bridges with Network Rail’s Engineer on site.
Anglesey, Betws-y-Coed then Hexham!
Mouchel’s then advised that there was major washout damage on the Blaeneau Ffestiniog and a risk of further floods returning, so diving inspections would be further delayed. Planned diving inspections in north Wales and Anglesey were due to start on Monday 17th January including the Britannia Bridge and the Valley Causeway. It was here that a diver died whilst working some years ago, but nonetheless the divers consider it a privilege to work on such a famous structure.
But on the morning of Tuesday 18th January a team was on site on the Ffestiniog branch to examine bridges 20 and 23 near Betws-y-Coed . Their examination confirmed that there were no problems, the stone piers being well pitched. But that same day there was an urgent call from Network Rail, requesting emergency inspections in the Hexham area.
Another fifteen bridges to dive
No fewer than fifteen bridges needed underwater examination on the Newcastle to Carlisle route and on the Darlington to Bishop Auckland and Eastgate Branch. Whilst it was easy for Bridgeway to muster a second diving team, the equipment was in the wrong place. Consequently a driver went to North Wales overnight, collected the necessary equipment and returned to head office in Nottingham so that the second team could start diving on the Hexham/Carlisle route on Wednesday morning. Their work was completed on Friday 21st January, and the lines were re-opened.
But although most bridges had suffered little if any damage, there were problems with Wetheral Viaduct. The depth of flooding can be judged by the tree trunk left behind on the pier in the picture. Protection to the foundations of this fine structure, in the form of rock armour or heavy pitching, was installed four years ago.
The floods had extensively altered the riverbed and washed away the rock armour. Nonetheless the foundations were still secure, and hence reopening could be recommended in the e-mailed report to Network Rail. The formal written report followed on the next Monday, drawing attention to the need to renew the rock armour protection.
As good as a ride at Alton Towers?
My thanks to all involved in diving inspections at Bridgeway Consulting. They do a job few of us would relish, especially in mid winter! But their commitment and enthusiasm is an excellent example of the dedication of our professional railway engineers.
Particular thanks to Brian Maddison, their managing director, who found the time to tell me about their involvement in restoring our railways after the floods. He still enjoys his diving and it is good to find a chartered civil engineer of his experience using his expertise in the front line- and I still don’t believe his assertion that being washed along a free flowing culvert beneath the railway is as good as a ride at Alton Towers!