History
The Nottingham and Melton Mowbray railway was originally opened in 1879 as a twin-track, connecting Kettering and Nottingham for both goods and passenger traffic. The line was eventually closed as part of the Beeching Axe in 1968, however British Rail retained the 13-mile long section from Edwalton to Melton Mowbray as a test track which is still in use today, now named the Rail Innovation and Development Centre.
Earthworks Failures
Over the weekend of 16-17th December 2023, a significant failure occurred on a section of embankment adjacent to the village of Old Dalby, Leicestershire. The site consists of a 700-metre long embankment which varies in height up to a maximum of 12 metres high, and supports two railway lines, the Up Reversable Line (URL) with OLE, 3rd rail, 4th rail and troughing with telecommunications and power cables and a Down Reversable Line (DRL) with OLE.
Whilst the above average rainfall and heavy down pours between October to December ultimately triggered the main earthworks failure, there were several other conditions leading to the gradual deterioration of the asset. Significant alterations to the track alignment have taken place since the railway was converted to a test track 60 years ago, with the railway initially being converted to a single line high speed test track, later re-introducing the second track including alterations to add electrification elements. Numerous sections of cess retention systems are present, assumed to have been installed to accommodate changes to track alignment over the years and support the significant depth of ballast, indicating historical issues maintaining line and level through the site. The soft clay core of the embankment fill will have contributed to the maintenance issues, and the higher than normal rainfall events this winter have elevated porewater pressures in the earthworks, eventually causing a steep rotational failure at the crest of the embankment, becoming more translational at the toe, leaving the railway hanging in mid-air.
Remedial Works
CML were appointed by Network Rail to undertake a Site Investigation along the 500-yard length of affected embankment and provide recommendations for monitoring and emergency remedial works. Remedial works were initially focused on repairing the main failure which would be crucial to re-opening the railway. The most cost-effective solution was determined to be via the construction of a granular fill berm which could be designed to fit within the railway boundary. Following substantial site clearance works, the team removed 17,000 tonnes of material from the shear key and the failed slope, whilst re-constructing the embankment benching in and compacting nearly 20,000 tonnes of engineering fill. The berm construction is now complete and handed over to the track and OLE teams to bring the test track back into operation.
Works are continuing at the site to address a further two less developed failures, which will be remediated with a combination of gravity retaining walls and sheet piled solutions. Over 370 linear metres of drainage is also planned to be installed to create a more resilient asset for the future.
