Case Study: Copyhold Lane Cutting – Slope Stabilisation
Client: Network Rail
Engineer: Tony Gee & Partners
Main Contractor: BAM Nuttall Ltd
Following a series of landslips onto the London to Brighton railway in winter 2006, BAM Ritchies was employed by the Southern Zone Construction Partnership to deliver an innovative scheme aimed at stabilising the 220m long cutting without restricting train movements.
Initially BAM Ritchies designed and built a temporary catch fence to protect the train line while the upper slope was re-graded to a shallower 30º. The regrading process removed 3,000m3 of weathered mudstone and was completed safely with the aid of live CCTV footage relayed to the driver and Ritchies’ rope access operatives.
Once the regrading works were completed, BAM Ritchies installed over 520 soil nails. Three air masts mounted on long reach and
CAT excavators were used to install the nine metres long x 25mm diameter GEWI bar soil nails on the upper slope, using neat cement grout mix. For the lower slope, soil nails were installed using in-house designed and built Terrapin rigs suspended by cables from the permanent top anchor blocks and some temporary anchors. Complex design issues and space constraints within the cess were overcome by the installation of flexible Geobrugg wire rope anchors. This innovative product and drilling method allowed works to be completed without the need for any possessions.
Following the installation of soil nails and in order to limit soil erosion and contain future debris material, rope access workers spread topsoil on the upper slope along with 3000m2 of NAG C350 matting to provide a stable growing medium for vegetation. This was finally covered with Maccaferri rock netting. The lower slope was treated with 900m2 of Macmat-R erosion matting in areas of weathered material while a 2,800m2.
Maccaferri rock curtain was installed in areas of more competent rock to contain future erosion, supported by over 2km of steel cable. Finally four 25m long x 160mm diameter boreholes were installed along the crest to act as soak away drains and take surface water away from the new slope.