Michael L. Roach.
The railway line we see today between Penzance and Truro was built as a single track by the Hayle Railway and the West Conwall Railway and later doubled by the Great Western Railway. The Hayle and West Cornwall Railways were both slightly quirky with a rich history which can be read on Wikipedia. There are eight railway viaducts in the 26 miles of track between the two towns but there were once nine. Despite this number of viaducts there are two deep valleys crossed by huge embankments, and I wonder why ?
The two large embankments are located in the villages of Brea and Carn Brea between Camborne and Redruth and are both around 20 to 25 metres high. When they were built in the 1830s any compaction of the fill material forming the embankments would have been primitive at best – perhaps a granite roller pulled by two horses; at worst no compaction at all. I think the reason for building embankments rather than viaducts are the long cuttings on both sides in an endeavour to make a reasonably level route through this mining district. It would have been very convenient to use the excavated material from the cuttings in the valleys and to balance the cut and fill. The material is likely to have been end-tipped into the valley leading to settlement for a number of years under self weight and the weight of the trains. The track would have to be packed up regularly to avoid a dip in the vertical alignment. These two embankments could be among the highest railway ones in Britain.
At the other end of the spectrum from the huge embankments mentioned above was the ninth viaduct which was dispensed with long ago. It was located just outside Penzance Station and was 347 yards long, which was the the longest between Penzance and Truro. Penzance Viaduct was just a few yards above ground level which was the foreshore of the beach with the tide coming and going beneath the viaduct. The viaduct was originally a timber trestle carrying a single line. This construction of a timber trestle across a beach was not unique but was quite rare in Britain. It is thought that all examples have been replaced. Maintenance costs were high due to regular damage by gales, so when the Cornish main line was being doubled it was quite natural to replace the viaduct with a stone-faced rubble embankment. The work was carried out between 1919 and 1921. In the last photograph of the attached article note what appears to be concrete fence posts which was most unusual for the time.
7056-8 Scans of an article which appeared in the Great Western Railway Magazine for June 1922
MLR / 21 April 2023