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Brunel’s Oxford to Birmingham railway line (it became part of the GWR) reached Harbury around 1850. The plan was for a tunnel through the land north of the village. Earth movements forced a change of mind. Instead, a cutting 2·5km long was dug by hand; its maximum depth was 34m (110 feet), the deepest in Europe at the time. A short tunnel was left to support the road north out of the village, the modern B4452.

The local geology has continued to provide challenges to infrastructure owners. The most significant landslip to occur in the Network Rail era occurred on the 30th January 2014: 400,000 tonnes of soil and rock from the Lower Jurassic period moved towards the railway. The remediation that followed was, it is understood, aimed at preventing a further classic rotational slump of the embankment.

A year later in 2015, almost to the day on 31 January, a 350,000 tonne landslip on the railway embankment at Harbury meant the line had to be closed. A further investigation of the geology revealed that the movement had been lateral: the pressure of groundwater that had built up behind an unsuspected wall of clay had been sufficient to slide it southwards over a stable rock surface.

Network Rail engineers secured and made the cutting safe by removing a huge volume of material. Soil nails were fitted to the slopes as part of the work to hold them in place, and drainage was installed to take away excess water. The line reopened to trains in March 2015. The slopes are being hydroseeded to create a grassy habitat that will attract wildlife back to the area.

I have a connection to these events. On a visit to London, 31 January 2015, I arrived back at Marylebone to get the train home only to find all trains cancelled north of Banbury. By showing my Chiltern ticket at Euston, as advised, I was able to travel by Virgin train to Birmingham, thence home to Warwick on a normal service. Next day I photographed the landslip site as best I could: SP3760 : Site of landslip, 31 January 2015, north side of Harbury Cutting.

Sources:
Network Rail website: Link
A talk by Luke Swain, CGeol, Senior Asset Engineer (Geotechnics) Network Rail, to the Warwickshire Geological Conservation Group, 20 April 2016. Link

Author: Robin Stott Link 9 June 2016

Interim information, subject to revision
The deep, curving cutting, about 2·5km long, has the 73 yard Harbury Tunnel at its heart. It was built for the Birmingham and Oxford Junction Railway to broad gauge proportions between 1847 and 1852, reportedly by I.K.Brunel. Originally it was intended to build a longer tunnel, but unstable ground resulted in a cutting 110 feet deep being constructed instead – the deepest man-made cutting in the world at the time. The cutting itself was widened around 1884 because of soil slippage – a problem that has not been entirely solved to this day. Information taken from the Warwickshire Railways website: Link