Structural Avalanche Defenses - mearsandwilbur.com 2012 Wilbur avalanche defense short... · Living...
Transcript of Structural Avalanche Defenses - mearsandwilbur.com 2012 Wilbur avalanche defense short... · Living...
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Structural Avalanche Defenses Chris Wilbur, P.E. Wilbur Engineering, Inc.
SW Colorado Chapter ASCE February 15, 2012
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Outline • Design Avalanche • Types of Structures
– Deflecting/Diversion – Dams & Retarders – Snowsheds – Snow Supporting – Direct Protection
• Example Project – Snoqualmie Pass, WA
The Battleship, US 550 Tim Lane Photo
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Snow Avalanches
1773 Engraving “Topographie der Schweiz”
David Herrliberger
2009 Diagram The Design of Avalanche Protection Dams
European Commission
Dense core
Powder component
Saltation zone
Entrainment
Tomas Johannsson & Peter Gauer
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Design Avalanche
• Probability • Avalanche type
– wet, dry, powder
• Consequences • Other factors
– Political – Economic – Legal
Swiss Federal Office of Topography
Robert Petley photo
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Design Parameters
• Flow velocity • Flow heights • Flow densities • Flow directions • Existing snow height • Snow erosion height • Geometry of structure
(Height, Deflection angle)
Figures from: The Design of Avalanche Protection Dams
European Commission, 2009
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Structural Defense Locations Starting Zone Structures
Deflection Structures
Dams/Retarding Structures
Direct Protection
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Diversion Structures
• Redirect flow • Small deflection angles • Deposition depends on
slope angle • Must consider
redirected flow impacts
Stoli Boli, Iceland PhotoReynir Vilhjálmsson
Selkingen-Biel, Switzerland Photo: Charlie Wuilloud
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Diversion Structures
Arinsal Andorra
Siglifjordur, Iceland
San Juan County, CO
Pitkin County, CO
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Dams & Retarding Structures
Neskaupstadur - Drangagil, Iceland
Pas de la Casa, Andorra
Galtur, Austria
Switzerland: Hans Frutiger photo
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Snettisham, AK
Photos: AEL&P
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Snow Sheds (Galleries)
Splugen Pass, Switzerland 1843 - 1950
Shed Loading – from Peter Schaerer ASCE Journal of the Highway Division 1966
Mine Conveyor, Grand County, CO
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Central Pacific Railroad Sierra Nevada Snowsheds
• Timber Construction • 1867-1869 • Two types:
• Avalanches • Snow protection
• 37 miles total • Fire problems • Replaced w/ concrete
& tunnels
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Great Northern RR Stevens Pass Snowsheds
Washington State Historical Society photos
Tye Shed, 1929
1913
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Wolf Creek Pass – US 160
Wolf Creek Pass 1966
Alberta Path & Alberta’s Cousin
Wolf Creek Pass 2010
Mark Mueller, CAIC photo
Hans Frutiger photo
• Site of 2 avalanche fatalities in 1950-51 • Built in 1965 after series of snowy winters • Shed impacted once in last 19 years • Shed removal likely at end of service life due to low return
period and effective forecast & control program
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East Riverside – US 550 • 3250’ Vertical fall • 80 acre starting zone • Reaches highway multiple times per year • 6 Persons Killed (since 1963) • Built in 1985 for $1.6 million • Recommended Length = 400’ • Constructed Length = 180’ • Design Loads:
• Static 1800 psf • Dynamic 1000 psf
Art Mears photo Art Mears photo
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Starting Zone Structures
Design Parameters • Max. Snow Height • Slope angle • Snow Density • Ground roughness • Aspect
Rigid Structures
Flexible Structures
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Flexible Starting Zone Structures Snow Nets
Jackson, Wyoming Pas de la Casa, Andorra
Mt. Crested Butte, CO Photo: Vela, Italy
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Rigid Starting Zone Structures
Davos Switzerland, SLF photo
Galtur, Austria
Concrete Structures
Photo: Hans Frutiger
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Direct Protection No off-site Land Required Protection/materials focused at
Resource Allows development in “Moderate
Hazard” Areas Usually Reinforced Concrete Steel, Masonry, Boulders also used Off-site deflections possible
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Ophir, Colorado Sun Valley Idaho
Sun Valley, Idaho
Ketchum, Idaho
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420 kV Line - Eastern Iceland
Reykjavik
NASA Photo
Hydroelectric Plant
Aluminum Smelter
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Direct Protection Photo: IceGrid
by Ragnar Jónsson
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Lessons from Europe 1999 • Severe Winter w/ extreme
avalanche conditions • Forests very effective • Starting Zone Structures very
effective; some overtopped • Dams caused new hazards &
damages • Powder component exceeded
mapped limits • Multiple events w/in single
path caused damage • Measured record velocities
(110 m/s or 245 mph)
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I-90 Snoqualmie Pass, WA
• 30,000 ADT • 35 million tons
freight/yr. • Cost of Closures • 1100’ Snowshed • 3700’ Snow nets • Ditches & Walls
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East Shed – Snoqualmie Pass
ES-2 ES-1 ES-3 ES-5 group ES-4
WSDOT photo
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Snoqualmie Pass East Shed
• 2 lanes • 500 feet long • 4:12 (33%) Roof pitch
Existing Snowshed (1951) Planned Snowshed (2012)
• 6 lanes • 1100 feet long • Roof pitch 5%
Artist’s conception by WSDOT
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Slide Curve Starting Zone Structures
• 1140m (3740’) structures • 3.0m, 3.5m & 4.0m heights • Special designs for high
density snow (400 kg/m3) • Instrumented for loads &
deflections • Afforestation
Photo: John Stimberis, WSDOT
WSDOT photo
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Design Climate Washington Cascades vs. Swiss Alps
1. Total Precipitation 2. Seasonal Differences 3. Temperatures 4. Rain-on-snow
Swiss Design Guidelines
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Snow Net Instrumentation
1. Uphill Anchor Tension 2. Post Compression 3. Post Inclination 4. Downhill Cable Tension
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Thank You!
1. Living and Dying in Avalanche County, John Marshall & Jerry Roberts, 1998 2. Avalanches and Snow Safety, Colin Frazer, 1978 3. Snow Avalanches Along Colorado Mountain Highways, Hans Frutiger, 1964 4. The Avalanche Handbook, David McClung & Peter Schaerer, 2006 5. RGS Story Vol. III, Vance Junction to Ophir, W. George Cook, Dell A. McCoy,
Russ Collman, Sundance Publications, Ltd., 2000.
Suggested Reading:
Photo: Mike Janes, AEL&P