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15 MountainRisks IntensiveCourse Barcelona 08 Corominas Tutorial QRA Andorra
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Transcript of 15 MountainRisks IntensiveCourse Barcelona 08 Corominas Tutorial QRA Andorra
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I n t e n
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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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I n t e n
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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))