Ground engineering specialist the Universal Group was contracted by Amco Rail to carry out the stabilisation of 21,000m2 of cutting on either side of a running line at Studley Grange, near Swindon.
The final design required the installation of 1,169 soil nails to a depth of nine metres on the north-facing cutting and another 1,428 soil nails to the same depth on the south-facing cutting.
To compliment the nails, a mesh system comprising Deltax mesh, steel rope and tension anchors was installed across the entire surface of both cuttings.
Under normal circumstances, Universal would have used a long-reach excavator with a TEI boom-mounted drilling head to install nails of this length.
But due to access restrictions and weight limitations at the crest of the embankment, this conventional soil-nailing plant was not an option.
“The only feasible alternative was to use traditional rope access rock drilling equipment,” says Universal’s joint managing director Richard Lowe, “but installing 9m-long, self-drilling nails into stiff clay and mudstone using this method 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 with the power and speed of a conventional excavator-mounted rig,” says Lowe.
“Our design and fabrication team rose to this challenge and developed a steel-tracked slope-climbing system with a powerful mounted drilling head, clamps and a telescopic mast, capable of installing 2.5m bars.”
Universal’s fitters stripped components, including hydraulic pumps, valves and controls, from an existing Italian-made Joy 2 rig and used these to build a new machine of their own design.
“The track base, chassis and mast were all bespoke – designed and fabricated entirely in-house,” says Lowe. The machine was then retro-fitted with a powerful Krupp drilling head on the mast.
Three of the rigs – dubbed ‘Slopeys’ by the contractor – 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, says Lowe.
“We actually only used two of the machines, they were so efficient,” comments Lowe. “We kept the other one in reserve as a spare.”
Power for the machines was provided by a remote hydraulic power-pack located at the top of the slope. Although the machines were capable of tracking up and down the slope under their own power, Universal used a system of ropes and winches to secure the rigs in the event of any movement.
“We placed two kentledge blocks at the top of the embankment and attached a powerful winch and ancillary lines to make sure the rigs were safe and secure on embankments and cuttings up to an angle of 45o,” says Lowe.
Rob Taylor, the firm’s other joint managing director, comments: “Our team are experienced in working in challenging environments including live railways and restricted access. We used innovative thinking to provide a smart solution to this complex brief.”
Taylor adds that, with an installation rate averaging 250 linear metres of soil-nail per rig/per shift, the job was completed three weeks ahead of programme, with zero incidents or accidents.
Lowe says that development of the Slopey design continued even throughout the contract with Amco. “We carried on tweaking the design during the job. For example, it originally had rubber tracks but we changed them to steel tracks when we found that we needed better traction on the slope,” he says.
While the new Slopeys were capable of installing most of the soil nails on this project, they couldn’t access the very bottom of the embankments and so Universal was obliged to use more commonplace methods – a buggy-mounted Marini rig – to install the nails at the bottom of the slope.
However, this served to demonstrate the superior capabilities of the custom-built Slopey machines, says Lowe. “Using the buggy-mounted rigs at the bottom we were installing five nails per day, using 1m-long rods,” he says.
“But the Slopeys were installing them in 2.5m lengths – and installing more than 20 per day,” he adds.
This article was first published in the March 2020 issue of The Construction Index magazine.
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