A 300t boulder was stabilized at Rest and Be Thankful mountain pass in Scotland
An innovative rock restraint system to secure a 300t boulder in Scotland was made possible by Parafil® Type F ropes, geocomposite materials with a Kevlar tendon core, protected by a polyethylene sheath, offering high strength with low strain. Parafil® ropes are manufactured by Linear Composites Ltd, a member of the Maccaferri Industrial Group.
Rest and Be Thankful is a mountain pass along the busy A83 trunk road between Arrochar and Inveraray in the Western Highlands of Scotland, UK. Following a debris flow, which initiated at 350 m above road level in early 2014, site investigation works identified the vulnerability of a large boulder, assessed to be in the order of 300 tons.
A protective action was needed but a controlled removal of the boulder would have been very dangerous. In fact, the boulder was acting as a ‘choke’ to material behind and above it and removal of this boulder would have resulted in another debris flow. Additionally, the safety and cost of disposal of the large quantity of blasted material that would have been produced, could not be assured to the client, Transport Scotland.
A Parafil® rock restraint system in conjunction with ground anchors was identified as the best way to achieve the stabilization of the boulder. Anchorage would be provided by double vertical steel anchor bars and double raking anchor bars cast into reinforced concrete mounting plinths to provide load bearing capacity and stability on the poor quality soils.
The Kevlar Parafil® Type F system was chosen to give the desired high strength, low weight and very long design life that this mountain-side installation would require.
Following temporary stabilization and monitoring of the boulder, anchors fitted with bespoke high-strength termination plates were installed into the slopes above. 90 mm diameter holes were then cored through the boulder to accept the tendons.
Each of the seven 45-ton capacity Kevlar tendons was connected to the bespoke, high-strength steel anchor plates using proprietary shackles, before being passed through the holes in the boulder and tensioned against the down-hill face of the boulder using post-tensioning terminations.
The tendons were positioned in a “fan” arrangement to maintain the stability of the boulder in both the along-strike and down-dip directions on the slope.
This complex and demanding phase of site work at Rest and Be Thankful was undertaken by local geotechnical specialist contractor, Georope, working in contract to BEAR Scotland. The design was undertaken by the Perth office of Waterman, in consultation with Georope and Maccaferri.
Parafil® is manufactured by Linear Composites Ltd, a member of the Maccaferri Industrial Group. It consists of parallel-laid fibers forming the strength element of the rope and a tough polymer protective sheathing. Numerous combinations of fibers and sheaths are available to suit the specific application and client demands.
Its benefits, when compared to metallic/synthetic alternatives, include a high strength-to-weight ratio, excellent chemical resistance, high UV resistance, excellent fatigue characteristics and stability over a wide temperature range. Due to its versatility, Parafil® ropes are used in multiple applications including catenary support systems, urban transport systems, sub-sea, oil and gas, military, marine and structural applications.
For more information, please download our case history.