Between 1847 and 1852, engineers attempted to build a railway tunnel at Harbury village in Warwickshire, UK, but the geology proved so unstable that they resorted to a cutting. The massive human undertaking was breathtaking, even by today’s standards. The workers hand dug the cutting, which was more than 104 ft deep and 600 ft wide. Limestone spoil from the mile-long cutting was put along the proposed line of the railway to form an embankment to the north. Geotechnical failures, particularly landslides, would blight the site for more than a century. Countless landslides eventually forced National Rail to undertake massive geotechnical ground investigations to redress the natural faults.
While working on a scheme designed to resolve these stability issues, construction and infrastructure contractor J Murphy & Sons encountered tension cracks, which appeared in the slope above the cutting. Investigations showed a previously unrecorded vertical fault at the back of the cutting. Work slowed to a crawl, but more misfortune befell the project. In late January 2015, a large landslide sent some 350,000 t of material crashing over the site. Construction was halted, and J Murphy hired experts to stabilise the slope and survey the geological features of the area.
Central Alliance, an RSK company, applied its considerable experience to stabilise the slope. With many geotechnical faults, the team’s original remit was expanded to install ground movement and groundwater monitoring instruments. Moreover, its survey personnel worked concurrently to undertake accurate georeferenced surveying. The data mined were instrumental in revealing the site geology and mapping a 3D model of the site. Drones armed with HD cameras mapped the entire area to detail the extent of the landslide, thereby helping to plan the remediation work. Installing dewatering wells and a full dewatering system helped to reduce groundwater levels, which minimised the risk of further instability during construction.
Central Alliance used its satellite monitoring solution to identify land movements over time on various areas of the site. The team’s regular long-term monitoring will help to detail how the land has responded to the remediation works. The company’s innovative technology has proved an invaluable source to improve knowledge of the land and ensure that the best recommendations and solutions can be put in place. The troublesome slope was covered in topsoil and turned into grassland.