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Rock falls represent a large percentage of landslide-related hazards reported by Canadian railways in mountainous terrain. A 54.7 km-long section of railway through the Canadian Cordillera is examined that experiences, on average, 18 rock falls each year. An approach for rock fall hazard management is developed based on quantified risk. The approach focuses on defining railway operation procedures (freight train operations and track maintenance) that comply with quantified risks. Weather-based criteria that define periods when rock falls are more likely to occur along the study area are examined. These criteria are used herein to reduce exposure to rock falls and reduce their consequences. Several freight train operation strategies are proposed that comply with a tolerable level of risk adopted in this study for illustrative purposes. The approach provides a simple, flexible and practical strategy for railway operations that can be regularly adopted by the operators, and that is based on a more comprehensive assessment of quantified risk. [ABSTRACT FROM PUBLISHER]

Relationships between weather conditions and rock fall occurrences have been acknowledged in the past, but seldom have such relationships been quantified and published. Rock falls are frequent hazards along transportation corridors through mountainous terrain, and predicting hazardous rock fall periods based on weather conditions can enhance mitigation approaches. We investigate the relationship between weather conditions and rock fall occurrences along a railway section through the Canadian Cordillera. Monthly weather-rock fall trends suggest that the seasonal variation in rock fall frequency is associated with cycles of freezing and thawing during the winter months. The intensity of precipitation and freeze–thaw cycles for different time-windows was then compared against recorded rock falls on a case-by-case approach. We found that periods when 90% of rock falls occurred could be predicted by the 3-day antecedent precipitation and freeze–thaw cycles. Some rock falls not predicted by this 3-day antecedent approach occurred during the first two weeks of spring thaw. These findings are used to propose a rock fall hazard chart, based on readily available weather data, to aid railway operators in their decision-making regarding safe operations. [ABSTRACT FROM PUBLISHER]

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Copyright of Canadian Geotechnical Journal is the property of Canadian Science Publishing and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Slopes in weakly cemented glaciolacustrine sediments in the Morkill River valley in the Canadian Rocky Mountains stand at up to 70°. Based on field and laboratory observations it appears that a contributing factor to instability is the softening of the soils by frost action and the leaching of calcite cement. Field density profiles demonstrated increased density and carbonate content with an increase in depth. Laboratory tests of carbonate content indicated a positive correlation between calcium carbonate and density in the glaciolacustrine sediments. The relationship was strongest in sands, in which leaching and dissolution were important components of softening. In clays, frost action was the dominant component of softening. Freeze-thaw tests showed a 50% decrease in strength after one cycle of freeze and thaw in the silts and clays.Key words: landslide, cemented, glaciolacustrine sediments, British Columbia.Les pentes dans les sédiments glaciolacustres dans la vallée de la rivière Morkill dans les montagnes Rocheuses canadiennes tiennent jusqu'à des angles de 70°. D'après des observations sur le terrain et en laboratoire, il semble qu'un facteur qui contribue à l'instabilité est le ramollissement des sols par l'action du gel et le lessivage du ciment de calcite. Les profils de densité du terrain ont montré une densité et une teneur en carbonate croissantes avec la profondeur. Des essais de teneur en carbonate en laboratoire ont indiqué une corrélation positive entre le carbonate de calcium et la densité dans les sédiments glaciolacustres. La relation était plus marquée dans les sables dans lesquels le lessivage et la dissolution étaient des composantes importantes du ramollissement. Des essais de gel-dégel ont montré une diminution de 50 % de la résistance après un cycle de gel et dégel dans les silts et les argiles.Mots clés : glissements de terrain, cimenté, sédiments glaciolacustres, Colombie Britannique.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]