On November 25th, 2012 a 53,000 cubic m rockslide buried the Canadian National Railway (CNR) track at Mile 109.4, Ashcroft Subdivision, near Boston Bar, causing a 4-day service disruption on their main east-west railway connection. The rock landslide resulted in the collapse of a 21 m long concrete rock shed originally designed to protect the railway from debris raveling out of a gully above the track. The landslide rupture surface is composed of vertical release fractures and exposed day-lighting discontinuities. A number of rock and debris landslide hazard types are identified in the post-landslide slope. The magnitudes, frequencies, and seasonal occurrences estimated for these hazards posed a significant short and long term risk management challenge for construction of the track protection structure. This paper focuses on lessons learned during ground hazard assessment, design and construction of a new 80 m long track protection structure. The first construction challenge was the short term protection of the work site from raveling rocks. This was managed with a rock fall mesh attenuation curtain combined with safe work protocol. The permanent composite barrier wall/rock shed structure consists of a tied-back, gravel-filled barrier wall designed to absorb a large portion of the impact loads during a future rock landslide event, and a rock shed allowing the rock landslide to safely travel over the railway track. All components are modular, facilitating construction under railway traffic to meet the goal of reducing track service disruptions.
Keegan, T., B. Willoughby, T. Edwards, M. Busslinger, M. Sturzenegger and A. Wen. 2014. “Construction of a Composite Barrier Wall/Rock Shed Structure at Mile 109.43 of CNR’s Ashcroft Subdivision,” in Geohazards 6: 6th Canadian Geohazards Conference, Kingston, ON, June 15-18, 2014. CGS (Canadian Geotechnical Society).
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