Rock Mass Fall – Rock Avalanche Design Loads for Railway Track Protection Structures

On November 25th, 2012 a 53,000 cubic m rockslide buried the Canadian National Railway (CN) main track at Mile 109.4, Ashcroft Subdivision, near Boston Bar, causing a 4-day service disruption. The rock avalanche resulted in the collapse of a 21 m long concrete rock shed for track protection. This paper describes the analyses carried out to derive impact loads for design of a new track protection structure including; i) description and characterization of the November 25th, 2012 event; ii) dynamic runout back-analysis; iii) forward-analysis to derive rock avalanche impact loads; and iv) interpretation of loads for structural design of a new composite barrier wall/rock shed structure. A modified version of the pseudo-three-dimensional runout analysis software DAN-W is used, allowing output of normal and shear stresses at the base of a sliding frictional mass. The software allows computation of centrifugal acceleration for each sliding mass element. Results show that peak normal and shear stresses are sensitive to sharp terrain breaks (i.e. changes of the terrain slope), due to centrifugal forces generated by the moving mass. Peak stresses occur in the frontal part of the rock avalanche. Stress magnitudes are sensitive to angle (or radius) of terrain break and incoming velocity. These findings were used to optimize the design of the new track protection structure to the loading from a rock avalanche hazard.

Busslinger, M., O. Hungr, T. Keegan, W. Wu, T. Edwards. 2014. “Rock Mass Fall – Rock Avalanche Design Loads for Railway Track Protection Structures,” in Geohazards 6: 6th Canadian Geohazards Conference, Kingston, ON, June 15-18, 2014. CGS (Canadian Geotechnical Society).

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