Item: Quantitative Risk Assessment for the Snoqualimie Pass Avalanche Bridges
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Title: Quantitative Risk Assessment for the Snoqualimie Pass Avalanche Bridges
Proceedings: International Snow Science Workshop 2014 Proceedings, Banff, Canada
Authors:
- Alan Jones [ Dynamic Avalanche Consulting Ltd., Revelstoke, BC, Canada ]
- Greg Johnson [ WSA Engineering, Castlegar, BC, Canada ]
- Kevin Dusenberry [ Jacobs Engineering, Bellevue, WA, USA ]
Date: 2014-09-29
Abstract: Interstate 90 is a primary transportation corridor that crosses the Cascade Mountains at Snoqualmie Pass, Washington, USA. The highway is currently undergoing improvements to replace aging infrastructure, increase ecological connectivity, add vehicle capacity, improve safety and reduce avalanche closures. On the east side of the Pass, avalanche risk from the seven East Shed avalanche paths will be mitigated by construction of two 365 m bridges that are designed to allow avalanches to pass underneath them. The bridges are designed to meet the project design criteria for dense flow impacts to the bridges and powder flow impacts to vehicles. In order to help structural designers achieve the bridges' design criteria, Monte Carlo risk simulation methods were used to determine probabilistic avalanche impact loads, deposit geometries and risk to vehicles and the structures. This method allows designers to assign a range of model input parameters, which provides a range of model outputs. This allows for uncertainties to be better accounted for than deterministic analysis, increasing confidence in model results. This paper discusses how probabilistic avalanche risk analysis was applied, its advantages and limitations for the bridge design. Verification of the probabilistic models followed traditional methods by comparing results to field observations, other models, and engineering judgment. Verification included creating 3D geometries using probabilistically determined volumes of snow, including seasonal sluffing below the bridges, snowfall, plowed snow, and avalanche deposits. Design work for these bridges is complete, and construction started in April 2014 as part of a USD $248 million highway improvement project.
Object ID: ISSW14_paper_O10.01.pdf
Language of Article: English
Presenter(s):
Keywords: Highway, bridges, quantitative risk assessment, probabilistic, Monte Carlo
Page Number(s): 261-269
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