avalanche risk assessment in populated areas · 2011-01-11 · avalanche risk assessment in...

Urban Habitat Constructions under Catastrophic EventsFINAL CONFERENCE. Naples, 16th - 18th September 2010

Aurélie Talon & Jean-Pierre Muzeau

Polytech’Clermont-Ferrand (CUST) - LaMI

Blaise Pascal University

Clermont-Ferrand - France

Avalanche risk assessmentin populated areas

Avalanche risk assessment In populated areasA. Talon & J.-P. Muzeau – B. Pascal Univ., France – COST C26 Final Conf., Naples, 16th - 18th September 2010

2/34

Context

Avalanche PersonsStructuresInfrastructuresCommunicationsEnvironmentEconomy

Damages on issues caused by an avalanche

Hazard

Issue Risk


3/34

Starting

Process

Impacts on issue

How to identify and to

characterize?

How to quantify and to

mitigate?

How to identify the consequence

scenarios?

Hazard

Issue Risk

Approach of Risk Analysis


4/34

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

Snowy coat forming

Snowy coat properties

Avalanche classification

Avalanche characteristics and actions

Content of the presentation


5/34

Snowy coat forming

Stratification of snowy coat

• Wind deposit

• 1 cm / 10 minutesComparison: 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


6/34


Mechanical properties of snow

Unit weight 20 kg/m3 for fresh snow

500 kg/m3 for old snow

Cohesion 8 to 35 kPa = 300 to 460 kg/m3

0 to 20 kPa < 300 kg/m3

Compression

resistancet=58.3 ( / ice)

2.65 for plane faces and beakers

t=79.7 ( / ice)2.39 for other kinds of snow

Young Modulus E=2642 02.826 (in kN/m2)


7/34


Snowy coat properties: grain types

Crystal of fresh snowFine grains

Beakers

Round grains

Pictures: courtesy of Météo France


8/34


Sintering phenomenon of snowGlass bridge

Increasing of the cohesion

but failure propagation due to the snowy coat rigidity

Anena


9/34


Three types of avalanches

• Powder snow avalanche

air Incorporation of snow

Avalanche front

Snowy coat


10/34




• Plate avalanche


11/34




• Plate avalanche

• Wet snow avalanche


12/34


Avalanche sequence

Starting zone

Track

Runout zone

Debris

Slope breaking up

Accumulation basin

Gorge

Bouting out cone

Upstream

Downstream

Departure area

Flow area

• FT: traction strength

•FR: resistance strength

When FT>FR: departure of the avalanche


13/34


Morphological classification of avalanchesArea Criterion Distinctive characters

Departure

Departure type

- Spontaneous departure: internal causes of snowy coat (spontaneous

avalanche)

- Provoked departure: external causes of snowy coat (provoked avalanche)

- non human (cornice, serac, animal, etc.) human

- involuntary (accidental avalanche) voluntary (artificial avalanche)

Departure shape

- Punctual departure: avalanche starting from a point (departure with a pear

shape or a cone)

- Linear departure: avalanche starting from a line (plate avalanche)

Snow

quality

Potentiality

of liquid

water

- Null: dry snow avalanche

- Poor: humid snow avalanche

- Important: wet snow avalanche

Cohesion

- Poor: pulverulent snow avalanche

- Poor to moderate: crumbly plate (stretch) avalanche

- Important: snow avalanche of hard plate

Type of

snow

- New: - non windswept: fresh snow or recognizable particles

- windswept: recognizable particles or fine grains

- Evolved: fine grains, plane faces, recognizable particles or round grains

Position of the

sliding plane

- In the layer of the snowy coat (surface avalanche)

- On the soil (bottom avalanche)


14/34


Morphological classification of avalanches

Area Criterion Distinctive characters

Flow

Land shape- Open slope (side avalanche)

- Lane or gorge (gorge avalanche)

Dynamic (or flow type)

- With a cloud of snow particles:

- at the front level (aerosol avalanche)

- behind the front (avalanche with a panache)

- Without a cloud (streaming avalanche)

Corrected snow- With

- Without

Presence of blocks and / or other

elements

- With (tabular blocks, ice, rocks, trees)

- Without

Deposit

Superficial roughness- Poor (fine deposit)

- Important (bad deposit: blocks, bowls)

Snow quality- Wet (wet deposit)

- Dry (dry deposit)

Visible soiling - With (soiling avalanche: earth, blocks, trees)

- Without (clean avalanche)


15/34


Powder snow avalanche

• Lengthwise profile of an avalanche: depends on the

wind direction

• Reference pressure: 10 kPa < Pd < 30 kPa

• Application height of Pd: all the height of the exposed

walls

Avalanche height: currently 30 to 40 m but may be > 100 m

• Application direction of Pd: wind direction


16/34


Powder snow avalanche

• Effects to be taken into account:

• direction of Pd: wind direction

Pd ( +10 kPa)

-0.2 to -0.5 Pd

-0.3 to -0.8 Pd

-0.2 to -0.5 Pd

Avalanche Avalanche


17/34


Wet snow avalanche• Lengthwise profile of an avalanche: 3 zones (accumulation,

flow, deposit)

• Reference pressure: 30 kPa

• Application height of Pd: case of non submerged

buildings

Re

d z

on

e

Blue zone

Wh

ite

zo

ne

4

m

5 m

2

m

qhF


18/34


Wet snow avalanche• Lengthwise profile of an avalanche: 3 zones (accumulation,

flow, deposit)

• Reference pressure: 30 kPa

• Application height of Pd: case of submerged buildings

Re

d z

on

e

Blue zone

Wh

ite

zo

ne

4

m

6 m

qhF

qvF

qpF


19/34


Wet snow avalanche

• Application direction of Pd: direction of the more

down graded slope

• Effects to take into account:

• normal stress: = c Pd

• tangential stress: = c Pd

c: shape coefficient that describes the interaction between

the work and the snow flow: c = 2 sin2

: coefficient of static friction: 0,2 0,4


20/34


Wet snow avalanche with carried items• This impact is to be added to the avalanche stresses

• Punctual stress of 25 cm of diameter:

• 100 kN for an avalanche of 30 kPa




21/34

Risk analysis results depend on analysis scale

Mountain Massif Slope Snowy coat

Global environmental

impacts

Local environmental

impacts

Economical, sociological

impacts

Behavioralknowledge

Scale of avalanche risk analysis


22/34


With a civil engineering point of viewMassif scale

Structural analysis: Functional analysis:

Workable massifs

Unworkable massifs

To be sure for humans

To be beneficial

To do not make damage on workable massifs


23/34


With a civil engineering point of viewSlope scale

Upstream

Starting zone

Flow area Downstream

Structural analysis: Accumulation basinGorgeBooting outcomeFauna and floraSkiers

Station personalHabitantsCommunication system

Ski lifts

Runout zone


24/34

Risk scenarios : slope scale

Searching of all chaining of events that can

lead to:– injured, dead

– economical losses

– material damages

– environmental losses

Simplified example of a risk scenario:

AvalancheSkier

seriously injured

Road cut

Evacuation of the skier at the stop area by station personal

Evacuation to the hospital impossible

Death of the skier


25/34


To collect knowledge on snowy coat all

over the massif and the slopes:

Modeling of the spatial snow deposit


26/34


To collect knowledge on snowy coat all

over the massif and the slopes:

Permanent investigationon avalanches (EPA)

Location map of avalanchephenomena (CLPA)

In France, it is provided and managed by:

Office National des Forêts (ONF): collection on the ground

CEMAGREF: centralization of the information and map making


27/34


Listing of the avalanche consequences by

the ANENA:October 2007 – September 2008

Repartition of the average number of fatal accidents and the number of deaths by avalanche type

Plate

UnknownLocalised


28/34


Listing of the avalanche consequences by

the SLF:2007 – 2008 period

Repartition of avalanche accidentsby slope downgrade


29/34

Time

Avalanche event

Risk preventionProtection against risks

Crisis management

RepairImprovement of the prevention and protection actions

Gravity

Probability

Inacceptable risk

Acceptable risk

Protection

Prevention



30/34


Prevention - Actions on constructionsOverall constructive disposals

– building grouping

Mutual protection, protection of circulations

On line

Rein

forc

ed

b

uild

ing

Avalanche

< 10 m < 10 m

On stem

Avalanche


31/34


Prevention - Actions on constructionsParticular constructive disposals• Foresee and access and an entrance on the non exposed

facades

• Design facades without hold-in corner when there are face to

the avalanche

Marc Givry

Bad solution

Need of reinforcement


32/34


Prevention - Actions on the snowy coat

Preventive releasing of avalanches

Avalhex balloonGenerate explosion of a balloon

blown up of Hydrogen & Oxygen Spherical blast wave

CatexWire bringing explosives

above the snowy coat

Rapin

GazexGas burst (mix of

propane & oxygen) Ancey

“Avalancheur”Pneumatic bowler of explosive arrows

Duveau

Davidof


33/34


Prevention - Actions on persons

• Information provided at the department level

• Information provided at the level of the ski

station

• Signalling of the avalanche risk

Yellow flag for poor or limited risks

Flag with black and yellow checked board important and marked risks

Black flag for very important risks


34/34


Protection

• Permanent active protection: reforestation, wind & snow

barriers, buzzard roof, tire racks, fillets…

• Permanent passive protection:

Valla, Rapin

Valla, RapinValla, RapinStem

Stopping dikeDeflectors

Urban Habitat Constructions under Catastrophic EventsFINAL CONFERENCE. Naples, 16th - 18th September 2010

Thank you for your attention

Avalanche risk assessmentin populated areas

avalanche risk assessment in populated areas · 2011-01-11 · avalanche risk assessment in...

Documents