A network of protective, rock-fall catch barriers from Maccaferri has been installed at Knockan Crag, one of the most important geological sites in the British Isles.
Knockan Crag, in the far North West of Scotland, is where British Geological Survey [BGS] geologists’ recognised the principles of thrust tectonics.
Their debate about what had happened at Knockan Crag helped scientific thinking take a quantum leap when it was realised that rocks could actually be moved sideways by enormous, global forces, causing the stacking of rocks which in turn results in the formation of mountain belts. Similar thrust faults have now been recognised in rocks around the world, including those in the Himalayas and the Alps.
So important is the site that a permanent “Rock Room” visitor centre has been established. The need to protect visitors from falling rock was the prime motivation for the installation of a network of hi-tec, rock-fall catchment barriers from geotechnical specialists, Maccaferri.
Above the Rock Room, the crag consists of a steep [typically 75 to 85 degrees] rock slope, 20m to 30m high with a shallower slope [typically 20 to 40 degrees] below, mainly covered with grasses, shrubs and exposed scree.
Scottish Natural Heritage, specified the installation of a rock-fall catch fence on the scree covered/grass slope to protect the Rock Room.
Consulting Design Engineers, URS, Derby Office proposed a Maccaferri CTR1000 rock fall barrier system. According to URS Design Engineer Adrian Koe, “We looked at a number of options and the CTR1000 system was the most cost effective solution, given the performance criteria and site conditions.”
The CTR 1000 barrier has the capacity to arrest a 1.2cum, 3320kg block travelling at 25.5m/second within 3.5m. “To put this in perspective, that’s the equivalent of a vehicle the mass of a Range Rover with five ample passengers, hitting the barrier at over 55mph” Added Mr Koe.
Specialist contractors, Skye Rope Access installed the barrier system which was supplied to site in prefabricated kits. These kits came with the majority of connections, cables and energy dissipater components factory-fitted to minimise installation variations.
Maccaferri’s CTR system claims rock-fall protection up to a maximum impact energy of 5000kJ, the equivalent of stopping a 16.5 tonne lorry travelling at 57mph, within a deflection distance of 5.6m. Independent tests undertaken by the University of Bologna, Italy, found that the Maccaferri ‘CTR’ range of barriers performed to “Category A” standard – the highest standard, as defined in the EU, ETAG 027 testing methodology. According to Maccaferri, their system is the only one currently available in the UK which carries European ETAG 027 compliance.
