In Canada, on the west side of the Fraser Canyon, British Columbia, along a short stretch of the Canadian Pacific railway track there have been over 110 rockfalls reported between 1975 and 2009 resulting in over eight train hits, one derailment and damage to rail infrastructure.
A detailed site investigation identified the rockfall source area approximately 270 metres above the track. The rockfalls were concentrated down a rockfall chute where a rockfall attenuater system was proposed to mitigate the rockfall hazard.
The 42 metre hybrid attenuator system was constructed as a hanging net system to intercept and dampen the rockfall energy in the major rockfall chute area. The design was intended to guide the rockfall trajectory under a tail drape, dissipating the kinetic energy of the falling rock. This type of system was also chosen because of its ability to reduce maintenance, particularly cost effective in a region that has such a high rockfall event rate and remote access.
The Geobrugg ROCCO high-tensile steel wire ring nets were used in the hanging rockfall attenuator system. In addition, sections of the system were designed to accommodate various anticipated rockfall impact load conditions over 1,000kJ. The ring net spanned both sides of the chute area.
Above the nearby tunnel portal with no fallout zone, as a protection a 32 metre GBE-500A rockfall barrier with TECCO high-tensile steel wire mesh was installed. The modular design of the GBE rockfall barrier enabled the system to be installed by helicopter into the pre-anchored ground plates in 30 minutes. The TECCO mesh was then 'curtained' between the posts along the top and bottom support ropes. The issues of site access and active train scheduling were accommodated by the quick installation of both systems. Construction required a 50 ton crane, a 20 metre reach man-lift, and a helicopter. The mitigation design for this site was developed by Wyllie & Norrish Rock Engineers.
Fig. 1. Installed attenuator ROCCO hanging ring net with installation site of GBE rockfall barrier above tunnel portal.
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