What went wrong

摘要

Excavated to a depth of up to 30 m through inter-layered mudstones and limestone, Harbury cutting is on a line built by the Great Western Railway in the 1840s. It is a particularly deep cutting and had to be widened in the 19th century because of slippages. The latest landslip occurred where it abuts Harbury Tunnel. Following a much smaller landslide elsewhere at the site in February 2014, Network Rail had been carrying out stabilisation work in the cutting. This included installing stone drains to alleviate elevated levels of ground water. Monitoring during this work is understood to have shown slight movement before Christmas and in January. When the slope failed at 14.30 on January 31, the crest of the cutting dropped 4 m, leaving a sheer face below ground level. Photographs suggest that a wedge of material dropped, forcing the rest of the slope outwards towards the railway. The retaining wing wall at the tunnel entrance was also disturbed.