This rail cutting near Nuneaton had suffered a number of historic landslips and posed an ongoing risk of instability, potentially leading to rock fall or landslides that could affect the railway. Varied geology posed a challenge, with the lower half of the cutting consisting of weathered soils and the upper half consisting of soil overlaying competent siltstone and mudstone at the tunnel portal.

A programme of remedial works were designed to address the instability issues, requiring 6m length R32 self-drilling hollow bar soil nails in the soil slope areas and 3m length 28mm solid bar rock bolts where rock was encountered. In total over 2200 soil nails and rock bolts were required, with 8500m2 of erosion matting and high tensile steel mesh facing then laid over the cutting slopes and secured to the anchorages.

CAN Geotechnical were enlisted to undertake the extensive vegetation clearance, specialist access and drilling work, utilising long-reach 360 excavators to undertake the drilling on the upper slopes. The bottom row of soil nails were drilled using RRV mounted drill masts during possession, which were then used to mounted a CAN designed bespoke 1.5m temporary catch fence to protect the line from any material dislodged, allowing on-slope drill rigs to drill on the mid and lower slope where the long reach plant could not reach safely with the line open.

Involved early in the scheme to provide ECI, CAN proposed several adjustments to the soil nailing design in order to minimise the soil nails that needed drilling during the limited possessions available. This value engineering halved the requirement for drilling within possession, significantly decreasing costs and programme. A complex programme was devised sequencing daytime working following possessions in each area of site, and the possession works were completed ahead of programme, with less possessions required overall than planned. With up to 6 drill rigs then working at a time the geotechnical element of the scheme progressed better than planned and finished ahead of programme, and on budget.

Duration:      5 months       

Client:            J Murphy & Sons, on behalf of Network Rail

Location:      Warwickshire, West Midlands