The end of February is extended by a day this year but it still seems to be frantically busy. For that reason alone, I have set aside two BoMs I had half prepared and come in with a very quick and very recent one.
A PDF version is available here.
Just this week I was out to look at the Foal Mead Viaduct in Langport. It was fenced off as a construction site so I diverted to Wagg Drove to look at this modestly skew bridge.
We are in the Somerset levels. There is a drain each side of the “drove” and they must be carried under the bridge. The fences are solid, the uprights are bullhead rail. I wonder how long they have been there?
The aluminium pole was an attempt to measure deflections under the passing high-speed trains to see whether we could get anything at 100mph. The bridge is buried under a couple of metres of fill so the loads would be distributed anyway.
There is some interesting movement in the bridge, some of which we photographed deliberately, while some I have only noticed in the photographs. A return visit is called for some time soon.
Let’s begin at the corner with two pics. The bricks were not cut to produce a flush finish, but that lowest one looks to have a lot of overhang. It is a false impression because the corner of the abutment has a bull nose and, in any case, the back corner is flush with the face as can be seen from a different angle.
People often tell me that the skew beds in the brickwork have some influence on the flow of force. The fact that the bricks here sit on a flush skewback surely gives the lie to that.
The stagger on the bricks is very variable. I think that is merely a result of the difficulty of setting out such a face though It might be something else as we will see below.
Here we can see how the stagger rapidly runs out on the face as we approach the crown. This is because the bricks at the crown meet the edge at a right angle. In the courses above, there is a strange banding effect. I have no immediate idea what has caused that.
The ground is very soft and that seems to have created problems for the wing walls. At the north west corner, the crack seems to run along the bottom of an upward extension. The pillar that forms the end of the wall has a vertical face while the wall is tilted slightly backwards. I think the designer, were he to do this again, might choose to set the whole inclined face back a little further rather than end up with this, slightly uncomfortable look. The crack in the picture below seems to stop at the pillar, but a closer look will show that the crack visible at the left here is a continuation.
Interestingly, there is no such cracking across the road from here. That is probably because the combination of the angle of the embankment, the road and the top of the wall means that the wall is rather longer.
Diagonally opposite is another short wall and rather more damage. The stripe of apparently different coloured bricks below the main crack have simply been repointed and are original.
The spandrel and its buttress have been pushed out too though. And though it isn’t prominent there is a crack at the top of the original wall where the brick colour changes.
The nosing course seems pretty straight here but the arch seems to wave in and out under it.
Near the crown there is a substantial overhang and the underside of the nose has a strip of mortar indicating how far out it has moved.
The most interesting point, though, is below the second tie from the left where the face of the arch seems to have tilted outwards.
Looking up more steeply, that is more obvious, though there is an alternative diagnosis that the ring has been patched here.
While we are looking up, it is worth noting that those are special pattresses, presumably cast for the job. The ties angle in along the skew line but also downwards into the backing behind the arch.
And I am afraid that will have to do. I will try to do better next month, though if the work piles up as it is, at the moment, I might not. Trouble is the lag between work and money is becoming a potential embarrassment.