THE WAMPOOL VIADUCT
One good thing about these satellite images that you can see on your computer is that all kinds of interesting relics are shown up in all kinds of strange places. Having accompanied me to the north side of the Solway Viaduct with Adrian, Carole was well into James Brunlees by now, if you pardon the expression. She was tracing the route of the Solway Junction Railway on one of these image sites when she called me over to look at some mysterious objects she had seen in the middle of the River Wampool just a short drive from the Solway Viaduct.
Knowing what it was that I was expecting to see, having studied the work of Brunlees and Bouch for as long as I have, it only took a glance to be able to say that what Carole had seen were the stumps of cast-iron columns that had once supported another of Brunlees' iron viaducts. Unexpected remains of this nature from a structure that was dismantled and sold for scrap 75 years ago could only lead to one conclusion, and at the next available opportunity I drove out to the area for a butcher's.
It didn't take me long to find the old track bed, and I knew that I was in the right place for the old Ordnance Survey map showed that there had been a railway station here. And sure enough, at the side of the track bed was "Station Farm", for the site of Whitrigg Station was just around here.
This really sums up everything that you need to know about the Solway Junction Railway. We are in what in Norfolk would be called the Fens, outlying marshy land surrounded by water and at risk of inundation by the sea. There's a tiny settlement here consisting of a farm and a couple of cottages, and this settlement merited a railway station for passengers on the line, such was the dearth of any larger settlements from which passengers could be solicited.
You can see what I mean about the fens and the marshy land if you just look in the foreground of this image. Tussocks of marsh grass are growing here amid pools of stagnant ater.
That line of trees and bushes running across the centre of the photograph is without doubt the old track bed of the Solway Junction Railway as it heads southwards to the site of the Wampool Viaduct which, you may be surprised to learn, was built to take the railway line over the River Wampool - sometimes known and spelt as the "River Whampool".
Seeing the line of the track bed was one thing. Actually negotiating myself onto it was another thing completely. In fact it was a good thing that I had come on my own for Liz and Carole who accompany me at times on some of my excursions suffer from health issues and are not as mobile as they might be.
While I was contemplating how to reach the track bed I poked the Pentax through the brambles to give you an idea of the view towards the viaduct.
In my youth, I had bent over backwards to be a limbo dancer and it was in exercising those skills that I finally arrived down at least somewhere near the track bed. That barbed wire and those gorse bushes were certainly some obstacle to overcome.
The muddy pool is an interesting feature and it would seem that formerly there was a railway overbridge that took the track across. I'm not quite sure though why the railway company didn't just simply fill it in.
If you accompanied me on my trip to the track bed in Scotland north of the Solway Firth, you would have seen some impressive stonework - some masonry of quality. So in the circumstances I'm not at all sure why they would have decided to use brick, and common brick at that, to build this railway bridge here.
In contrast to the stonework, the brickwork has clearly seen better days and has shaled. This is a phenomenon caused by using an incorrect mixture of mortar that does not correspond with the constituency of the bricks. Differences in temperature and moisture cause the bricks to expand and contract and if the mortar is made too hard, the bricks on expansion crush up against the solid mortar bands and this causes the shaling.
With some effort I found myself on the track bed of the Solway Junction Railway, looking southwards in the general direction of the viaduct.
The railway line was abandoned in 1921 when the Solway Viaduct was found to be unsafe and the track around here was finally lifted in 1937. Whether or not the ballast was removed at the time, it is long gone now. The embankment is simply bare earth and is used as a cattle trail across the marsh.
A brisk walk along the track bed brought me into sight of the River Wampool. Just here the river is tidal, and at the moment the tide is out. You can see how high the tide rises by looking at the debris "hanging on the old barbed wire" in the manner of the Sergeant-Major in the soldiers' ballad of World War I. As an aside ("you'll get used to these" - ed) the German Army's equivalent of bully-beef in World War I was known as "barbed-wire entanglement".
In the background are the radio masts of the Anthorn Very Low Frequency radio station near Cardurnock - all thirteen of them.
Bingo! This is what the butler ... er ... Carole saw when she was looking at that satellite image the other day. And I you can see that I was dead right with my guess of what they might be.
The casting of columns for the support of a viaduct is a complicated process and to cast them in one piece was impossible given the technical constraints under which these Victorian foundries were operating at the time. What they did was to cast them in sections, and bolt them together on site.
The lowest cylinder of the column would usually be driven into the ground until it reached solid bedrock or some other foundation. Sometimes a system of caissons - hollow cylinders filled with rubble or concrete - would be sunk onto the river bed where solid bedrock was too far down, as at the Tay Bridge, and the lowest cylinder would be erected upon the caisson.
Given the marshy ground around here, I'm intrigued to know how they managed for foundations. I've heard it said that piles were driven into the river bed for a depth of 30 feet but whether they were timber piles or iron caissons filled with concrete I've not been able to find out. But the foundations are the most important part of the construction. It was the false borings of the river bed that misled Bouch into his flawed design for the foundations of the original Tay Bridge and resulted in a hasty redesign.
Once the lower cylinder had been successfully installed, the other cylinders would be bolted on top, and the whole column would then be braced against a neighbour. With a long, high bridge it would be usual for the columns in the same row to be braced against the row behind and the row in front. The purpose of this is to prevent what is known as "racking" - the bridge leaning in line with the movement of a passing train, taking up the free play in the expansion joints. For reasons best-known to himself, Sir Thomas Bouch omitted this necessary feature in his Tay Bridge.
Given the low height and short length of the Wampool Bridge it is doubtful that there would be any provision required for heat expansion and hence no precaution against "racking" would be necessary.
If the viaduct was high above the ground in an area where strong winds could reasonably expected, outriggers, called "rakers" would be added. These would be stepped out from the viaduct at ground level and lean in to the bridge at rail height so that the principle of triangular bracing would take effect. A triangle is a much more stable support than a rectangle - look at the diagonal cross-bracing in a simple plank door, and of course a traditional bicycle frame is just two triangles joined together.
From the photo above however, it's clear that the viaduct could not have been much above 20 feet so I imagine outriggers were not used. Brunlees used piers of 6 columns, including outriggers, in constructing the Solway Viaduct just up the road. Here there are only 4 columns in a pier.
Having said that, however, the effects of wind on a structure were little-known in the mid-19th Century and it is true to say that the collapse of the Tay Bridge contributed greatly to the awakening of the realisation of the problem. Major-General Hutchinson of the Railway Inspectorate, the body designed to inspect railway structures before their opening to the public and the man responsible for the certification of Bouch's Tay Bridge, was asked at the Tay Bridge Disaster enquiry whether he considered that the allowance of even 20 pounds per foot in the structure for wind resistance would have been extreme.
"I really cannot tell you. I had no knowledge to go upon. I have of course heard a good deal since ... (the disaster)" he replied and you can feel the anguish in his reply.
Don't forget that in the mid 19th Century the Board of Trade had figures for the loads per foot to be borne by different qualities of iron, the load per foot for different trains - all that sort of thing. If the Board had no figures for wind resistance, who can blame the designer?
Brunlees, having relentlessly and remorselessly criticised Bouch at the Enquiry for having built the Tay Bridge with no allowance for wind resistance, was obliged to admit under cross-examination by Bouch's counsel that he had never made allowance for the wind in any bridge that he had designed - including a viaduct that was 170 feet high, almost twice the height of the Tay Bridge, across a ravine in Brazil.
You only have to read the examination and cross-examination of Brunlees at the Tay Bridge Enquiry (questions 15490 to 15731) to realise what an opportunist and blusterer Brunlees really was.
The faces of the cylinders would need to be turned on a lathe to ensure that the fitting was perfectly flat. If there were any kind of nib on the faces, this would prevent the columns from being perfectly vertical. A small angle out of the vertical at ground level could magnify itself to quite a distance at a high level. If the columns were out of the vertical the stresses of the trains crossing the viaduct would not be evenly distributed, and if the lean of the column was such that the top of the column (and hence the girders carrying the weight of any train) was outside the footprint of the base of the column, then the weight distribution would be such that a collapse of the bridge sooner or later would be inevitable.
The presence of nibs can also give a false indication of tightness. The bolts might be tightened up to their fullest extent but the cylinders would be resting on the nibs. Action of the wind and stresses from trains on the viaduct would cause friction on the faces that would grind down the nibs and the bolts would be no longer tight.
On Bouch's Tay Bridge, many of the cast faces were not turned down despite his instructions and the action of the wind and passing trains ground down these rough faces to such an extent that many of the supporting cotters worked loose. Henry Noble, the maintenance engineer, packed the loose cotters with shims of metal without informing Bouch. And he packed them with the bridge out of tension. From then on the bridge would no longer come back into tension and so it warped with the winds.
It is also a wise precaution to have the cylinders cast so that there would be a male protusion on the bore at one end and a female indentation in the bore on the other. On assembly the male part of one cylinder would fit into the female part of the next cylinder. This gives the column an added rigidity.
Despite Brunlees' superior manner at the Tay Bridge enquiry, it's quite clear that his columns don't have the male and female parts to the cylinders.
It was the view in this photograph that finally undermined, at least in my mind, any moral superiority that Brunlees might possibly have had, even had his testimony at the Tay Bridge Enquiry come up to proof (which, of course, it didn't, and by a long way too). Have a close look at the cylinder on the left of those three here.
Do you see the vertical line running down the side of this cylinder? It's clear that it has been horizontally cast and that the molten iron was not hot enough at the time of pouring. The iron has cooled before it has encircled the core of the mould and a skin has formed on the surfaces of the iron. When the molten iron encircled the mould and met itself at the other side, if you see what I mean, this skin would prevent a proper fusion. This is known as a "cold shut" and is a desperate weakness in a casting process.
How a cylinder should be cast is in the vertical or upright position. That way the core of the mould is always encircled by the molten metal and it would be almost impossible to create a "cold shut", although I'm sure that there would be some casters who would manage somehow to achieve one.
I must admit that I had a little smile when I saw this "cold shut" in this cylinder. For all of Brunlees' pontificating about how he could build the perfect bridge, much better than anything that Bouch could build, he's still casting vertically and getting "cold shuts" in his work.
One thing that I really wanted to do was to go down as close to the columns as I possibly could. Apart from cold shuts that we have already seen, I wanted to check for blistering and scabbing of the columns and the presence of the infamous Beaumontague, or "Beaumont Egg" as it is known in the foundry vernacular.
In casting, all of the impurities such as carbon, solid iron, foundry slag and air bubbles rise to the top as they are less dense than the molten iron. In the more correct vertical casting, an efficient foundry would cast a cylinder taller than that specified in the plans. All of the impurities would float to the top into the oversize, which would then be turned off in a lathe.
But all of this is time-consuming, labour-intensive and expensive. It's much cheaper and quicker to cast horizontally and having seen the cold shut, I'm convinced that these cylinders were cast horizontally.
When objects are cast horizontally, all of the impurities still float to the top, but "top" is actually the side of a cylinder. These impurities being less dense that the cast iron, are lighter and so makes the column that much weaker on the one side.
Now just imagine the situation where ...
i.... a column has been horizontally cast
ii... there are impurities in one side so that it is weaker than the other side
iii.. the faces of the cylinder, not having been ground flat, have irregular and uneven surfaces that cause the cylinder to lean out of the vertical. The weight is now resting on the weaker side of the cylinder rather than perpendicularly through the whole column
iv... an untrained and ill-informed inspector, noticing that the tie bars that hold the bridge in tension are no longer in tension for they were measured for when the bridge was perfectly upright, but now the bridge is leaning out of the vertical due to the rough-cast faces having been ground smooth by the friction generated by the wind nd passing trains. So he packs the bridge with shims of steel, locking it into the out-of-the-vertical position
v.... a strong blast of wind, stronger than anything that had ever been measured up to that date, suddenly blows up the river
vi... just at that precise moment, a train is passing over a column that is weak down one side due to the impurities caused by vertical casting and which is leaning over so that all the weight loading is passing down the weaker side
and there, ladies and gentlemen, you have the Tay Bridge Disaster in a nutshell.
The impurities in a casting are extremely visible, especially the air bubbles that resemble pockmarks. The cylinders cast at Wormit for the Tay Bridge were riddled with pockmarks and evidence was given at the Tay Bridge enquiry that some of the air bubbles went right through the casting. So how did the moulders hide them? They resorted to the old foundry trick of filling them with Beaumontague, which is a mixture of, would you believe, beeswax, fiddlers' resin, iron filings and lamp black. This was what I was hoping to see.
I also wanted to check to confirm that the columns here were indeed cast iron. Two thoughts were going round in my mind - firstly that they were in pretty good condition for abandoned cast-iron, and secondly that if they had been cast-iron, why hadn't the dismantlers tried harder to pull them up? If they aren't cast-iron I can see me rewriting this page in something of an embarrassed hurry.
So I slid down onto the riverbank just here and found myself embedded in quicksand. This was not such a good idea, especially as I was on my own, and it took me a good few minutes to extricate myself. No wonder the dismantlers left the lower cylinders in place.
I'll be back here again in due course, but with a scaffolding plank. And also a friend, if I have any. But my next stop had to be the Leven and the Kent viaducts, built by Bouch across Morecambe Bay for the Furness Railway. And by pure coincidence there was a festival of Morris Dancing at Ulverston, just up the road from these viaducts, and I had been invited to attend.