The GWR, aware that the new line would finally enable them to run trains into the heart of the City, invested almost £250,000 in the scheme. Eventually, over a five-year period, £1m was raised. The chosen route ran beneath existing main roads to minimise the expense of demolishing buildings. Originally scheduled to be completed in 21 months, the construction of the underground line took three years. It was built just below street level using a technique known as ‘cut and cover’. A trench about ten metres wide and six metres deep was dug, and the sides temporarily held up with timber beams. A two-metre-deep layer of soil was laid on top of the tunnel and the road above rebuilt.
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