Challenges In The Rockfall Hazard Rating System: An Atlantic Canada Case Study

J Nichols

In the proceedings of: GeoVancouver 2016: 69th Canadian Geotechnical Conference

Session: GEOHAZARDS - VI Climate Change Floods & Landslides

ABSTRACT: The globally-recognized standard for rating rockfall hazardsalong transportation corridorscanfail to capturekeygeological and environmental factorsincertain environments. TheNational Highway InstituteRockfall Hazard RatingSystem (NHIRHRS)was developed to rapidlyassessand qualitatively rate individual sections within a slope inventory.However, oversimplification of certain geological and environmental categories can cause challenges when evaluatingpotentialhazardsusing this approach.In Atlantic Canada,geologicaland environmental conditions change rapidly over relatively small geographical distances.When conditions change rapidly over a short distance, comparatively ranking sections becomesincreasingly subjective.TheNHIRHRS was implemented for a slope management study of 75 km of theCabot TrailHighwayin Cape BretonHighlandsNational Park,Atlantic Canada.In this study,we demonstrate thattheNHIRHRS oversimplifiesthe geologicaland environmental variabilityalong theCabot TrailHighwaywhich resultedinchallenges when qualitatively ranking theslopes within the inventory.The incorporation oftheremote sensing techniqueof digital photogrammetryallowed foramore effective rock slope managementprotocolinthis geologically and environmentally extreme environment.R•SUM•La norme mondialement reconnue pourles risques associ†sde rockfall peut d†former les facteurs g†ologiques etenvironnementaux dans certains environnements. LeNational Highway InstituteRockfall Hazard Rating System (NHIRHRS) a †t† d†velopp† pour acc†der rapidement et qualitativement †valuer les sections individuelles dans un inventairede pente. Cependant, simplisme de certaines cat†gories g†ologiques et environnementales peut causer des probl‡meslors de l'†valuation des risques potentiels.Au Canada Atlantique, les conditions g†ologiques et environnementales peuvent changer rapidement sur derelativement petites distances g†ographiques. Lorsque les conditions changent rapidement sur une courte distance, leclassement relativement sections devient un d†fi de plus en plus subjective.La NHI RHRS a †t† mis en …uvre pour une †tude sur la gestion de la pente de 75 km de la CabotTrialHighway dans leparc national des Hautes-Terres-du-Cap-Breton, le Canada atlantique. Dans cette †tude, nous d†montrons que la NHIRHRS simplifie la variabilit† g†ologique et environnementale le long du sentier route Cabot qui pr†sente des d†fis lorsdu classement qualitatif des pistes dans l'inventaire. L'incorporation de la technique de t†l†d†tection de photogramm†trienum†riqueautoris†epour un protocole de gestion des talus rocheux plus efficace dans cet environnementg†ologiquement et environnemental extr—me.1INTRODUCTIONArockfall eventof any scalealong any transportationcorridorcan create considerableriskfor injury and causeextensivedamageto property or infrastructure.Rockfallhazardsoccur when rock or debris is shed onto thetransportation corridor from anearby slope(Vandewateret al.2005).Because the majority of transportationcorridors have been in service for decades and thenumberof vehiclestraveling on them has dramaticallyincreased, the problems related to rockfall have becomemore severe and common (Pierson2012).Overtime, increased weathering of the joint surfacescause slopes to lose strength and become moresusceptible to rockfall events(Pierson 2012).Many factorscome intoplaywhen assessing therockfallriskassociated with a transportation corridor. Some factorscan be controlled during construction,such as slopeheight, road width,ditchgeometryand slope angle;whereasothers areinherentto thesetting, such asclimate and geology.1.1Rockfall Hazard Rating SystemThe seriousness of rockfalleventshasled to thedevelopmentof a proactive rockfall management systemtermed theRock Hazard Rating System(RHRS).Thesystem was originally developed by Pierson (1991) for theOregon Department of Transportation, andhassince

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