1. GIS-based 3D modelling for landslide hazard assessment: Séverine Bilgot Aurèle Parriaux

2. Introduction  6% of the Swiss territory affected by landslides  Occurrences and potential damages always increasing  Necessity to have objective and easy to update hazard maps 2

3. Identification of susceptibility factors Intrinsic factors:  Resisting forces  Cohesion  Friction (depends on ,  ) , c,   For rock material: =f(geotype, grade, D, GSI)  For loose material: =f(granulometry, plasticity) 3

4. Identification of susceptibility factors Intrinsic factors:  Resisting forces  Cohesion  Friction (depends on ,  )  Driving forces  Gravity (depends on ,  )  Percolation (depends on i) i= grad h  Measured piezometric level (boreholes, springs, etc)  Spatial distribution of K 4

5. Identification of susceptibility factors Extrinsic factors:  Vegetation 5

6. Identification of susceptibility factors Extrinsic factors:  Vegetation  Permafrost melting Depending on:  Location (altitude, aspect)  Susceptibility of the formation =f(granulometry, plasticity) 6

7. Identification of susceptibility factors Extrinsic factors:  Vegetation  Permafrost melting  Anthropic impact 7

8. Methodology 8 Factor of safety Hazard map Hydraulic gradient Predisposition map 3D parameters model

9. Methodology 9 Hazard map Hydraulic gradient Predisposition map Factor of safety 3D parameters model

10. Integration of pre-existing data 10 Collecting data from previous projects Integrating them in a geodatabase 

11. Field mapping  Phenomena  Geology  Discontinuities  Formations  Fracturation, grade and GSI  Granulometry and plasticity  Hydrology  Springs and wet areas  Supposed associated aquifer  Vegetation  Structures 11

12. Methodology 12 3D parameters model Hazard map Hydraulic gradient Predisposition map Factor of safety

13. 3D parameters model  Determination of the 3D limits of the structural units  Kriging of the dips and strikes in each structural units  Modelling the rock formations with respect to field observation, boreholes information, profiles and dip and strike interpolation  Modelling the loose formations with respect to field observation, boreholes information, profiles and modelled rock formations  Kriging of the parameters inside each polygone or using the database 13

14. 3D parameters model 14

15. Methodology 15 Hazard map Hydraulic gradient Predisposition map Factor of safety 3D parameters model

16. Hydraulic gradient evaluation  Connecting each piezometric level, spring or wet area to the corresponding aquifer  Evaluating the geometry of each aquifer according to the repartition of K in the model  Interpolating the hydraulic head in each aquifer  Calculating the hydraulic gradient 16

17. Methodology 17 Hazard map Hydraulic gradient Predisposition map Factor of safety 3D parameters model

18. 3D factor of safety calculation  Calculation of the FoS at each sliding level indicated on boreholes  For each (x,y) couple, calculation of the FoS at each intersection with faults  For each (x,y) without calculated FoS < 1, calculation of the FoS at each z step, keeping the lowest value 18

19. Methodology 19 Predisposition map Hazard map Hydraulic gradient Factor of safety 3D parameters model

20. Predisposition map  Applying bayesian probability model to evaluate the weight of frozen soil, vegetation and anthropic infrastructures in the susceptibility to landslides  Calculating the predisposition map  Verifying the coherence of the predisposition map with respect to the map of phenomena 20

21. Methodology 21 Hazard map Hydraulic gradient Predisposition map Factor of safety 3D parameters model

22. Hazard map 22

23. Conclusion: at local scale  Applicable on most of instable areas (already tested on 10 sites in Switzerland and 2 in Kyrgyzstan)  Allows full transparency of the results and easy updates  Data can be easily re-used (high interoperability)  Only one common software to use  Toolboxes can be used separately in other domains (natural resources management, tunnel engineering, etc)  In order to reduce the costs and to provide better results, development of equivalent plugins for GRASS (in progress) 23

24. Indicative maps  Data infrastructure and standardize process allows to change the scale easily  Methodology applicable at larger scale with simple Quaternary structures (without lenses):  Using boreholes data and databases to evaluate the parameters  Using geoportals and aerial photographies for maps of phenomena, vegetation and anthropic impact 24

25. Thank you for your attention! severine.bilgot@epfl.ch