9oct mechanics large-landslides5

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9oct mechanics large-landslides5

  1. 1. Simon Fraser University Engineering Geology and Resource Geotechnics Research Group Understanding the Mechanics of Large Landslides Doug Stead, Simon Fraser University and Erik Eberhardt, University of British Columbia
  2. 2. Outline 1. What is the role of damage mechanisms in large landslides? 2. What is the role of kinematics in large landslides? 3. How can we model damage and kinematics effectively in large landslides? SFU
  3. 3. St Jouin Bruneval July 2013 VIDEO-FRACTOGRAPHY – a window on damage and kinematics
  4. 4. Damage and Kinematics 1 2 3 4
  5. 5. Rock Slope Damage Spatial Damage • • • • • • Slope topography Failure surface morphology Failure surface geometry Failure mechanism Lithological variations Geological structure Dx – along slope Dy – in slope Dz – depth DT – Time Temporal Damage • Geologic processes • Tectonics – deformation phases, uplift-erosion • Geomorphic processes – • Earthquakes • Groundwater/Thermal • Long term creep • • • • Preconditioning Initiation Failure Post-failure SFU
  6. 6. External and Internal Slope Damage Tension cracks Sackungen Frank Slide Palliser, AB Newhalem SFU
  7. 7. VAJONT : Geomorphic External Damage VAJONT : Geomorphic External Damage APPROACH • Geomorphic damage mapping to constrain mechanisms and models • Consider landform evolution and influence on slope failure mechanism – “Geomorphic Stress Path” Wolter et al. 2013 SFU
  8. 8. Damage - Failure Surface Geometry & Mechanisms PLANAR ACTIVE-PASSIVE SLAB UNDULATIING FLEXURAL TOPPLING MULTIPLANAR DAMAGE SHAPE FACTOR SFU
  9. 9. Structural Controls on Rock Slope Damage SFU
  10. 10. Lithological Controls on Rock Slope Damage SFU
  11. 11. Temporal Damage: Monitoring SFU
  12. 12. Simulated Inverse Velocity and Crack (Damage) Development in SLOPE MODEL Damage Zone SFU 12
  13. 13. Kinematics and Block Shape: Pentahedral wedges SWedge RocScience 2013 SFU 13
  14. 14. Rotation vs. Translation 3DEC Rock Cut Vajont Aknes Siromodel SFU
  15. 15. Release Surface: Questions TYPE INFLUENCE ON MECHANISM – DAMAGE/MOVEMENT DIRECTION INFLUENCE ON VOLUME (Runout) IS 2D OR 3D ANALYSIS REQUIRED ? PERSISTENCE-SPACING CONSIDERATIONS – Rock bridges? GEOMORPHIC RELEASE – LANDFORM EVOLUTION INFLUENCE OF EXCAVATION GROUNDWATER/IN-SITU STRESS SFU
  16. 16. Release Surfaces and Kinematics SFU
  17. 17. Modelling Damage and Kinematics TOOLBOX SELECTION OF MODEL TYPE LIMIT 2D or 3D ? CONTINUUM HYBRID DISCONTINUUM EQUILIBRIUM “Adapt the model to the problem NOT the problem to the model” “Large Landslides are an Energy-Damage System” SFU
  18. 18. Brittle Fracture Modelling: ELFEN SFU
  19. 19. Brittle Fracture Modelling: UDEC VAJONT Gao 2013 SFU
  20. 20. UDEC and 3DEC Brittle Fracture SFU 20
  21. 21. Importance of Kinematics – Vajont Prandtl Zone Models stable unless: • block size decreases kinematic release • internal deformation is allowed internal strain accommodation 2D – Phase2 Wolter et al. 2013 Prandtl Zone 3D – 3DEC 3D – Slope Model SFU
  22. 22. Slope Model Damage Simulation - Vajont • Point cloud (airborne LiDAR) derived geometry • Discontinuity sets are derived from photogrammetry and field mapping • Groundwater is considered implicitly (i.e. decreased friction angle) and explicitly Wolter et al. 2013 SLOPE MODEL: Point-masses connected by Springs SFU 22 Cundall, 2011
  23. 23. VAJONT PHOTOGRAMMETRY
  24. 24. f=800mm PHOTOGRAMMETRY
  25. 25. Preliminary Vajont Slope Model- Dry Model fracturing Before failure Wolter et al. 2013 Model displacement After failure SFU 25
  26. 26. Preliminary Groundwater Model G.W. 300 m Sliding surface Havaej et al. 2013 SFU 26
  27. 27. Conclusions 1. Damage is a fundamental component of the mechanics of large landslides 2. Extensive records exist of external damage 3. More limited data on internal damage but recognized as extremely important (a “damage front” concept) 4. It is important to consider the inter-relationships between failure kinematics and brittle rock fracture in rock slopes 5. Preliminary work show possible relationships between deformation and rock bridge fracture. 6. Improved characterization of large landslides should combine and fully utilize the latest developments in remote sensing-monitoring and modelling technologies. SFU

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