Urban Habitat Constructions under Catastrophic Events FINAL CONFERENCE. Naples, 16 th - 18 th September 2010 Avalanche risk assessment in populated areas Aurélie Talon & Jean-Pierre Muzeau Polytech’Clermont -Ferrand (CUST) - LaMI Blaise Pascal University Clermont-Ferrand - France
Context Issue Risk Hazard Avalanche Persons Damages on issues Structures caused by an Infrastructures avalanche Communications Environment Economy 2/34 Avalanche risk assessment In populated areas A. Talon & J.-P. Muzeau – B. Pascal Univ., France – COST C26 Final Conf., Naples, 16 th - 18 th September 2010
Approach of Risk Analysis Issue Risk Hazard Starting How to How to identify How to identify quantify and to and to the consequence Process mitigate? characterize? scenarios? Impacts on issue 3/34 Avalanche risk assessment In populated areas A. Talon & J.-P. Muzeau – B. Pascal Univ., France – COST C26 Final Conf., Naples, 16 th - 18 th September 2010
Content of the presentation Snowy coat forming Snowy coat properties Avalanche classification Avalanche characteristics and actions Scale of avalanche risk analysis System analysis : massif scale and slope scale Risk scenarios : slope scale Quantification of avalanche hazard Quantification of avalanche consequences Mitigation techniques 4/34 Avalanche risk assessment In populated areas A. Talon & J.-P. Muzeau – B. Pascal Univ., France – COST C26 Final Conf., Naples, 16 th - 18 th September 2010
Snowy coat forming Stratification of snowy coat • Wind deposit • 1 cm / 10 minutes Comparison: Loess 1 cm / century Stratification variability • Temporal variability: hourly, daily (day, night or morning/afternoon), weekly, annually, hundred years old, millenary • Spatial variability: vertical or lateral centimeter, meter or decimeter 5/34 Avalanche risk assessment In populated areas A. Talon & J.-P. Muzeau – B. Pascal Univ., France – COST C26 Final Conf., Naples, 16 th - 18 th September 2010
Snowy coat properties Mechanical properties of snow 20 kg/m 3 for fresh snow Unit weight 500 kg/m 3 for old snow = 300 to 460 kg/m 3 8 to 35 kPa Cohesion < 300 kg/m 3 0 to 20 kPa ice ) 2.65 t =58.3 ( / for plane faces and beakers Compression resistance ice ) 2.39 t =79.7 ( / for other kinds of snow 2.826 (in kN/m 2 ) E=2642 Young Modulus 0 6/34 Avalanche risk assessment In populated areas A. Talon & J.-P. Muzeau – B. Pascal Univ., France – COST C26 Final Conf., Naples, 16 th - 18 th September 2010
Snowy coat properties Snowy coat properties: grain types Fine grains Crystal of fresh snow Round grains Beakers Pictures: courtesy of Météo France 7/34 Avalanche risk assessment In populated areas A. Talon & J.-P. Muzeau – B. Pascal Univ., France – COST C26 Final Conf., Naples, 16 th - 18 th September 2010
Snowy coat properties Sintering phenomenon of snow Glass bridge Increasing of the cohesion but failure propagation due to the snowy coat rigidity Anena 8/34 Avalanche risk assessment In populated areas A. Talon & J.-P. Muzeau – B. Pascal Univ., France – COST C26 Final Conf., Naples, 16 th - 18 th September 2010
Avalanche classification Three types of avalanches • Powder snow avalanche air Incorporation of snow Avalanche front Snowy coat 9/34 Avalanche risk assessment In populated areas A. Talon & J.-P. Muzeau – B. Pascal Univ., France – COST C26 Final Conf., Naples, 16 th - 18 th September 2010
Avalanche classification Three types of avalanches • Powder snow avalanche • Plate avalanche 10/34 Avalanche risk assessment In populated areas A. Talon & J.-P. Muzeau – B. Pascal Univ., France – COST C26 Final Conf., Naples, 16 th - 18 th September 2010
Avalanche classification Three types of avalanches • Powder snow avalanche • Plate avalanche • Wet snow avalanche 11/34 Avalanche risk assessment In populated areas A. Talon & J.-P. Muzeau – B. Pascal Univ., France – COST C26 Final Conf., Naples, 16 th - 18 th September 2010
Avalanche classification Avalanche sequence Starting zone Track Upstream Slope breaking up Runout zone Accumulation Departure basin Debris area Gorge • F T : traction strength Flow area Downstream • F R : resistance strength When F T >F R : departure of the Bouting avalanche out cone 12/34 Avalanche risk assessment In populated areas A. Talon & J.-P. Muzeau – B. Pascal Univ., France – COST C26 Final Conf., Naples, 16 th - 18 th September 2010
Avalanche classification Morphological classification of avalanches Area Criterion Distinctive characters - Spontaneous departure: internal causes of snowy coat (spontaneous avalanche) Departure type - Provoked departure: external causes of snowy coat (provoked avalanche) - non human (cornice, serac, animal, etc.) human - involuntary (accidental avalanche) voluntary (artificial avalanche) - Punctual departure: avalanche starting from a point (departure with a pear Departure shape shape or a cone) - Linear departure: avalanche starting from a line (plate avalanche) Potentiality - Null: dry snow avalanche of liquid - Poor: humid snow avalanche Departure water - Important: wet snow avalanche - Poor: pulverulent snow avalanche Snow Cohesion - Poor to moderate: crumbly plate (stretch) avalanche quality - Important: snow avalanche of hard plate - New: - non windswept: fresh snow or recognizable particles Type of - windswept: recognizable particles or fine grains snow - Evolved: fine grains, plane faces, recognizable particles or round grains Position of the - In the layer of the snowy coat (surface avalanche) sliding plane - On the soil (bottom avalanche) 13/34 Avalanche risk assessment In populated areas A. Talon & J.-P. Muzeau – B. Pascal Univ., France – COST C26 Final Conf., Naples, 16 th - 18 th September 2010
Avalanche classification Morphological classification of avalanches Area Criterion Distinctive characters - Open slope (side avalanche) Land shape - Lane or gorge (gorge avalanche) - With a cloud of snow particles: - at the front level (aerosol avalanche) Dynamic (or flow type) - behind the front (avalanche with a panache) Flow - Without a cloud (streaming avalanche) - With Corrected snow - Without Presence of blocks and / or other - With (tabular blocks, ice, rocks, trees) elements - Without - Poor (fine deposit) Superficial roughness - Important (bad deposit: blocks, bowls) - Wet (wet deposit) Deposit Snow quality - Dry (dry deposit) - With (soiling avalanche: earth, blocks, trees) Visible soiling - Without (clean avalanche) 14/34 Avalanche risk assessment In populated areas A. Talon & J.-P. Muzeau – B. Pascal Univ., France – COST C26 Final Conf., Naples, 16 th - 18 th September 2010
Avalanche characteristics and actions Powder snow avalanche • Lengthwise profile of an avalanche: depends on the wind direction • Reference pressure: 10 kPa < P d < 30 kPa • Application height of P d : all the height of the exposed walls Avalanche height: currently 30 to 40 m but may be > 100 m • Application direction of P d : wind direction 15/34 Avalanche risk assessment In populated areas A. Talon & J.-P. Muzeau – B. Pascal Univ., France – COST C26 Final Conf., Naples, 16 th - 18 th September 2010
Avalanche characteristics and actions Powder snow avalanche • Effects to be taken into account: • direction of P d : wind direction -0.3 to -0.8 P d -0.2 to -0.5 P d -0.2 to -0.5 P d Avalanche Avalanche P d ( +10 kPa) 16/34 Avalanche risk assessment In populated areas A. Talon & J.-P. Muzeau – B. Pascal Univ., France – COST C26 Final Conf., Naples, 16 th - 18 th September 2010
Avalanche characteristics and actions Wet snow avalanche • Lengthwise profile of an avalanche: 3 zones ( accumulation, flow, deposit ) • Reference pressure: 30 kPa • Application height of P d : case of non submerged buildings Blue zone White zone 2 m Red zone 5 m 4 m q hF 17/34 Avalanche risk assessment In populated areas A. Talon & J.-P. Muzeau – B. Pascal Univ., France – COST C26 Final Conf., Naples, 16 th - 18 th September 2010
Avalanche characteristics and actions Wet snow avalanche • Lengthwise profile of an avalanche: 3 zones ( accumulation, flow, deposit ) • Reference pressure: 30 kPa • Application height of P d : case of submerged buildings Blue zone White zone Red zone q vF 6 m q pF 4 m q hF 18/34 Avalanche risk assessment In populated areas A. Talon & J.-P. Muzeau – B. Pascal Univ., France – COST C26 Final Conf., Naples, 16 th - 18 th September 2010
Avalanche characteristics and actions Wet snow avalanche • Application direction of P d : direction of the more down graded slope • Effects to take into account: • normal stress: = c P d • tangential stress: = c P d c: shape coefficient that describes the interaction between the work and the snow flow: c = 2 sin 2 : coefficient of static friction: 0,2 0,4 19/34 Avalanche risk assessment In populated areas A. Talon & J.-P. Muzeau – B. Pascal Univ., France – COST C26 Final Conf., Naples, 16 th - 18 th September 2010
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