Tutorial on QRA Rockfall hazard risk assessment. Andorra la Vella, E. Pyrenees

Transcription

1 Tutorial on QRA Rockfall hazard risk assessment. Andorra la Vella, E. Pyrenees Jordi Corominas Department of Geotechnical Engineering and Geosciences Civil Engineering School. Barcelona UPC

2 What is the problem? Location of Andorra la Vella (AV) Santa Coloma

3 What is the problem?

4 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?

5 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 level P(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

6 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 magnitude P(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

7 Identification of rockfall sources

8 Definition of basin and associated talus slopes Spatial unit: basin

9 How often? P (R) Couloir of Couloir Couloir of Pica Couloir of of Couloir Coll Luixent of d'eres Passader Cirera Roques Blanques Couloir of Couloir Couloir of Boneta of Alzina Forat Negre Apr m Jan-1997 May-2001 Basora Mateu Dec-1983 Jan Basera rock wall wedge Jan , 1984, other events between these years About ten events between 1956 and 1985 Several events before 1974 End of decade 1962 Rockfall of known age Rockfall with only an approximate age Plot of tree-ring sampling Ramenada Roc de Apr-1999 Between Jul-1998 and Jan-1999 Sant Vicens rock wall

10 Frequency (P R ) P R = 1/T R Estimated return Site period from: Historical record Forat Negre 5 Alzina couloir 15 Boneta and Cirera couloirs 10 Bassera Mateu > 25 Ramenada couloir 50 Coll d'eres couloir 25 Pica couloir 25 Frequency obtained at the base of the talus slopes

11 Preparing magnitude-frequency relation Location Location Percentage of block of different volumes 0,5 1 2, m 3 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 Percentage of blocks of different volumes >5 m 3 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

12 Assessment of travel distance (P (T:R) ) Frequency obtained at the talus slope. Not necessary

13 Impact probabillity (P (S:T) ) and (P (S:P) ) P (S:T)1 = L E /L D P (S:T)2 = L B /L E

14 Impact probability on buildings Location Length talus (m) L D Impact probability Length buildings (m) L E Width of exposed flat (m) L B Forat Negre Alzina couloir Boneta couloir Basera Mateu Ramenada c Coll d Eres c L E L B L D Block size (m 3 ) L R Cubic root (m) 0,

15 Vulnerability (V)

16 Case 2: one line of rockfall fences Rockfall fences: 6 m height 2000 KJ absorbed kinetic energy

17 Preparing magnitude-frequency relation Location Percentage of block of different volumes 0,5 1 2, m 3 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

18 Individual risk of lost of life k ( ) P = P P P P P V (ILOL) (R) (T:R) (S:T) (T:P) (S:P) (D:T) i i i=1 Different block sizes will give different values of P (S:P) K is the number of block-size classes P (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

19 Assessment of travel distance (P (T:R) ) Numerical modelling

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