The Churchland’s Cutting forms the southern approach to the well-known Harbury Tunnel and reaches a maximum depth of 34m at the tunnel portal. It was created along with the northern approach cutting, known as Harbury Cutting, when the tunnel was built in the mid 19th century. With the cuttings formed at steep angles in blue lias clays lying over a bed of limestone, instability has plagued the cuttings with landslips throughout their life.
A major earthworks scheme remediated the Harbury Cutting end of the tunnel following a significant landslip in 2016, where 326,000T of loose soil and rock slipped onto the line, and J Murphy & Sons were again enlisted to undertake a further package of cutting stabilisation work at the Churchland’s Cutting end of the tunnel in 2020.
A combination of a partial regrade along with a contiguous piled retaining wall, consisting of 149no. 750mm dia piles, was chosen to stabilise the Churchland’s end of the cutting. Whilst this solution could deal with the side slope of the cutting, potential instability of the soil slopes above the tunnel portal required a more specialist solution in the difficult access location, and a soil nail and facing system was developed to address this area.
CAN were enlisted to carry out vegetation clearance using rope access techniques, and then installed a bespoke temporary works catch fence along the top of the portal during possession. This protected trains running below, allowing 790no soil nails, up to 6m length, and 3000m2 of mesh and erosion matting facing to be safely installed with the line open. A combination of long reach excavator mounted drill rigs, and specialist slope climbing rigs for the more difficult access areas were utilised.
Duration: 16 weeks
Client: J Murphy & Sons
Location: Harbury, Leamington Spa