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Building the last Main Line Railway
Catesby Tunnel and Viaduct: gcrcs189
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View of the 'Survey Station' erected by the contractor above
Catesby tunnel to aid its construction. The survey station would have been
built in a location and at height that would maximise its line of sight.
Because the tunnel was nearly 3000 yards long there would have been several of
these structures over the top and in line with the path of the tunnel beneath.
They would have incorporated both a bench mark, for calculating height which
would be required for ensuring the tunnel's horizontal accuracy, a datum point
for ensuring correct alignment along its length. The reason for their being was
because the bore was driven from at least 8 intermediate shafts and from both
ends of the tunnel. Each intermediate point would see the bore be driven in two
directions thus at least 18 faces would be in operation reducing the
construction time significantly. On the right of the picture, a line of well
laid contractor's railway leads towards the headgear and temporary structures
surrounding shaft No 7.
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