Thanks to Guy N here are a few pictures taken around the bridge to show what is under there and for you to understand the reasons why the line needs to drop down by about 18", or about 45cm for those viewing on modern equipment.
There are a series of beams positioned under the existing bridge deck which are then supported on a structure parallel to the running line, this is encased in concrete below track level. Here you can see a general view of the arrangement that has been in place for many years. The important points are that there is sufficient space between the vertical columns for trains to pass and that the clearance under the bridge needs to be adjusted by the depth of the cross beams.
A closer look shows the spacing of the beams and the supports with their diagonal cross bracing
Under the bridge each cross beam is locked to it's neighbour at multiple points and the load is transmitted to the supporting structure by these pillar jacks.
In the last view you can just see the original brick arched infill, the newer beams and placed directly under the original beams so that they provide the additional strength necessary to take the 40 or so tonnes of modern trucks, quite a different load from when the bridge was first built for the passage of horses and carts
Further pictures of the excavations will appear shortly. It's thirsty work with the dust and heat, even taking the pictures is quite a job so many thanks to Guy.
Until next time.
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