15 MountainRisks IntensiveCourse Barcelona 08 Corominas Tutorial QRA Andorra

8/17/2019 15 MountainRisks IntensiveCourse Barcelona 08 Corominas Tutorial QRA Andorra

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Tutorial on QRA

Rockfall hazard risk assessment.

Andorra la Vella, E. Pyrenees

Jordi Corominas

Department of Geotechnical Engineering and

GeosciencesCivil Engineering School. Barcelona

UPC


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What is the problem?

Locationof Andorra la Vella (AV) –Santa Coloma


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For QRA we need answers to the following questions

Where the rockfall will take

place?

How often?

How far will it travel?

What magnitude (intensity)

will it have?

What are the potential

damages?


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Risk for properties (i.e. buildings)

R(P) = P(L) x P(T:L) x P(S:T) x V(D) X C

R(P): expected annual loss due to landsliding (€/yr)

P(L): probability of occurrence of a landslide of a given

magnitude

P(T:L): probability of a landslide reaching the building levelP(S:T): probability of the building being on the landslide path

V(D): vulnerability of the building

C: cost of the building

the analysis must consider all landslide magnitudes and all the

potentially affected buildings


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Risk for persons (i.e. inside a house)

Individual risk

R(ILOL) = P(R) x P(T:R) x P(S:T) x P(T:P) x P(S:P) x V(D)

R(ILOL): annual probability of loss of life

P(R): probability of occurrence of a rockfall of a given

magnitudeP(T:R): probability of a rockfall reaching the house level

P(S:T): probability of the house being on the rockfall path

P(T:P): probability of the person being in the house

P(S:P): probability of the person being in the rockfall path

V(D): vulnerability of the person


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Identification of rockfall sources


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Definition of basin and associated talus slopes

Spatial unit: basin


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How often? P(R)

C o u l o i r

o f

L u i x e n t

P a s s a d e r

C o u l o

i r

o f

C i r e r a

C o u l o i r o f R o q

u e s

B l a n

q u e s

C o u l o i r

o f

P i c a

C o u l o i r

o f

C o l l

d ' E r e s

C o u l o i r o f

C o u l o i r

o f

B o n e t a

F o r a t N

e g r e

A l z i n a

o f

C o u l o i r

B a s e r a

w e d g e

Basora Mateu

rock wall

Jan-1996

1974

Dec-1983

End of1960-69

decade

May-2001

Jan-1997

Several events

before 1974

Jan-19941968, 1984, other

events betweenthese years

Apr-2000

1962

About ten events

between 1956 and1985

250 m

Rockfall ofknown age

Rockfall with only

an approximate age

Plot of tree-ringsampling

R a m e n a d a

Apr-1999

Between

Jul-1998 and

Jan-1999

Roc de

rock wall

Sant Vicens


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Frequency (PR

)

Estimated returnperiod from:Site

Historicalrecord

Forat Negre 5

Alzina couloir 15

Boneta and Cirera

couloirs10

Bassera Mateu > 25

Ramenada couloir 50

Coll d'Eres couloir 25

Pica couloir 25

PR = 1/TR

Frequency obtained at the base of thetalus slopes


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Preparing magnitude-frequency relation

Location Percentage of blocks of

different volumes≤1 1-5 >5 m3

Forat Negre 83,5 15,97 0,51

Alzina couloir 83,5 15,97 0,51 Boneta couloir 83,5 15,97 0,51 Basera Mateu 83,5 15,97 0,51

Ramenada c. 83,5 15,97 0,51 Coll d’Eres c. 83,5 15,97 0,51

Location Percentage of block of different volumes0,5 1 2,5 5 10 m3

Forat Negre 49,6 33,9 14,5 1,47 0,51

Alzina couloir 49,6 33,9 14,5 1,47 0,51

Boneta couloir 49,6 33,9 14,5 1,47 0,51 Cirera couloir 49,6 33,9 14,5 1,47 0,51 Basera Mateu 49,6 33,9 14,5 1,47 0,51 Ramenada c. 49,6 33,9 14,5 1,47 0,51 Coll d’Eres c. 49,6 33,9 14,5 1,47 0,51 Pica couloir 49,6 33,9 14,5 1,47 0,51 Pica talus 49,6 33,9 14,5 1,47 0,51


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Assessment of travel distance (P(T:R)

)

Frequency obtained at thetalus slope.

Not necessary


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Impact probabillity (P(S:T)) and (P(S:P))

P(S:T)1 = LE/LD

P(S:T)2

= LB

/LE


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Impact probability on buildings

Location Impact probabilityLength

talus (m)

LD

Length

buildings

(m) LE

Width of

exposed

flat (m) LB

Forat Negre 180 180 10 Alzina couloir 150 70 10 Boneta couloir 190 140 10 Basera Mateu 310 28 10 Ramenada c. 130 20 10 Coll d’Eres c. 120 120 10

LE

LD

LB

Block size (m3)LR

Cubic root (m)

0,5 0.794

1 1

2.5 1.357

5 1.710

10 2.154


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Vulnerability (V)


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Case 2: one line of rockfall fences

Rockfall fences:

6 m height

2000 KJ absorbed kinetic

energy


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Preparing magnitude-frequency relation

Location Percentage of block of different volumes0,5 1 2,5 5 10 m3

Forat Negre 49,6 33,9 14,5 1,47 0,51

Alzina couloir 49,6 33,9 14,5 1,47 0,51

Boneta couloir 49,6 33,9 14,5 1,47 0,51 Cirera couloir 49,6 33,9 14,5 1,47 0,51 Basera Mateu 49,6 33,9 14,5 1,47 0,51 Ramenada c. 49,6 33,9 14,5 1,47 0,51 Coll d’Eres c. 49,6 33,9 14,5 1,47 0,51

Pica couloir 49,6 33,9 14,5 1,47 0,51 Pica talus 49,6 33,9 14,5 1,47 0,51

Case of Forat Negre basin


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Individual risk of lost of life

( )k

(ILOL) (R) (T:R) (S:T) (T:P) (S:P) (D:T)

i = 1i i

P = P × P × P × P × P × V∑

Different block sizes will give different values of P(S:P)

K is the number of block-size classesP(R), P(T:R) and P(S:P) depend on block size

For P(T:P), two scenarios have been considered:

The most exposed person: 20h/24h = 0.83

Average person: 14h/24h = 0.58


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Assessment of travel distance (P(T:R))

Numerical modelling


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Rockfall fence efficiency: new (P(T:R))

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15 MountainRisks IntensiveCourse Barcelona 08 Corominas Tutorial QRA Andorra