The final design required the installation of 1,169no 9m deep soil nails on the north-facing cutting and 1,428no 9m soil nails on the south-facing cutting. To complement the nails, a mesh system comprising of Deltax mesh, steel rope and tension anchors were employed across the full surface of both cuttings.
Due to access restrictions and weight limitations at the crest, conventional soil nailing plant was not an option. The only feasible alternative was to use traditional rope access rock drilling equipment, but at 9m long self-drilling soil nails into stiff clay and mudstone, this would have been a slow and expensive solution, especially when considering the number of nails to be installed.
"The challenge was to develop a rig with the capability to safely manoeuvre up and down the cutting but had the power and speed of a conventional excavator mounted rigs," said Richard Lowe, MD. "Our design and fabrication team rose to this challenge and developed a steel tracked slope climbing with a powerful mounted drilling head, clamps and a telescopic mast, capable of installing 2.5m bars."
A powerful winch and ancillary lines would make the rigs safe and secure on embankments and cuttings up an angle of 45 degrees. 3nr ‘Slopeys' were specially designed, built, tested and approved for this project. The modified steel tracks glided up and down the cutting and the fixed mast and powerful head installed the 9m soil nails with great efficiency.
"Our accomplished team are experienced in working in challenging environments including live railways and restricted access," said Rob Taylor, MD. "We used innovative thinking to provide a smart solution to this complex brief."
With an installation rate averaging 250lm of soil nail per rig/per shift, the job was completed three weeks ahead of programme, with zero incidents or accidents.