landslide risk assessment_Lanni_Pretto

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landslide risk assessment_Lanni_Pretto

  1. 1. My experiences after Master SIGEO and LARAM School Cristiano Lanni, Ilaria Pretto University of Trento
  2. 2. PRESENTATION OUTLINES: 1st step: Landslide risk assessment 2nd step: evaluation of shallow landslide Susceptibility and Hazard map using advanced methods 3th step: tutorial on quantitative risk assessment
  3. 3. PRESENTATION OUTLINES
  4. 4. 1) Which type of landslide? TYPE OF MOVEMENT TYPE OF MATERIAL VARNES, 1978
  5. 5. 1) Which type of landslide? SOME EXAMPLES
  6. 6. SOME EXAMPLES
  7. 7. SOME EXAMPLES
  8. 8. δ SOME EXAMPLES
  9. 9. Earth Slide Earth flow SOME EXAMPLES
  10. 10. LANDSLIDE IDENTIFICATION IS NOT ALWAYS AN EVIDENT TASK Understanding maps (topographic, geomorphological,..) Morphological evidences, deposits, vegetation, indirect evidence
  11. 11. 1) Which type of landslide? Understanding maps Aerial photo-interpretation
  12. 12. 1) Which type of landslide? MORPHOLOGICAL EVIDENCES
  13. 13. 1) Which type of landslide? MORPHOLOGICAL EVIDENCES
  14. 14. 1) Which type of landslide? DEPOSITION AREA kinematic reconstruction Type of material
  15. 15. 1) Which type of landslide? DEPOSITION AREA kinematic reconstruction Type of material
  16. 16. 1) Which type of landslide? DEPOSITION AREA kinematic reconstruction NEW STREAM PATH
  17. 17. 1) Which type of landslide? VEGETATION – INDIRECT EVIDENCE
  18. 18. This is an essential part of any landslide zoning. It Landslide Inventory (I): involves the location, classification, volume, travel distance, state of activity and date of occurrence of landsliding in an area. Landslide Susceptibility (S): Areas prone to slope failure or that where a landslide may travel onto or retrogress into it. Landslide Hazard (H): The probability of occurrence within a specified period of time and within a given area of a potentially damaging phenomenon. Elements at Risk (Er): Means the population, properties, economic and social activity, etc., at risk in a given area. Vulnerability (V): Means the degree of loss of a given element or set of elements at risk of a given magnitude. It is expressed on a scale from 0 (no damage) to 1 (total loss). Specific Risk (Rs): Means the expected degree of loss due to a particular natural phenomenon. It may be expressed by the product of Hazard times Vulnerability Total Risk (R): Means the expected number of lives lost, person I S H R injured, damage to property, or destruction of economy activity due to a particular natural phenomenon, and is therefore the product of specific risk and element at risk
  19. 19. I S H R
  20. 20. I
  21. 21. I S
  22. 22. I S H
  23. 23. I S H R
  24. 24. R = ( H × V ) × Er = Rs × Er I S H STEFAN €
  25. 25. Type of zoning I S H R
  26. 26. The SCALE REGIONAL SCALE SMALL SCALE < 1:100,000 MEDIUM SCALE 1:100,000 – 1:25,000 BASIN SCALE LARGE SCALE 1:25,000 – 1:5,000 DETAILED SCALE > 1:5,000 LOCAL SCALE
  27. 27. The PURPOSE Indicative Typical Area Range of zoning Example of Zoning Application LANDSLIDE INVENTORY AND SUSCEPTIBILITY SMALL SCALE < 1:100,000 > 10,000 km2 TO INFORM POLICY MAKERS AND THE GENERAL PUBLIC LANDSLIDE INVENTORY AND SUSCEPTIBILITY 1:100,000 – 1,000 – ZONING FOR REGIONAL DEVELOPMENT, OR MEDIUM SCALE 10,000 km2 VERY LARGE SCALE ENGINEERING 1:25,000 PROJECTS. PRELIMINARY LEVEL HAZARD MAPPING FOR LOCAL AREAS LANDSLIDE INVENTORY, SUSCEPTIBILITY AND HAZARD ZONING FOR LOCAL AREAS. LARGE SCALE 1:25,000 – 100 – INTERMEDIATE TO ADVANCED LEVEL 1:5,000 1,000 km2 HAZARD ZONING FOR REGIONAL DEVELOPMENT. PRELIMINARY TO INTERMEDIATE LEVEL RISK ZONING FOR LOCAL AREAS AND THE ADVANCED STAGES OF PLANNING FOR LARGE ENGINEERING Several INTERMEDIATE AND ADVANCED LEVEL STRUCTURES, ROADS AND RAILWAYS DETAILED SCALE > 1:5,000 Hectares to HAZARD AND RISK ZONING FOR LOCAL AND 1,000 km2 SITE SPECIFIC AREAS AND FOR DESIGN PHASE OF LARGE ENGINEERING STRUCTURES, ROADS AND RAILWAYS INTERNATIONAL GUIDELINES (FELL ET AL., 2008)
  28. 28. Recapping: I I S WHERE Frequency Assessment (of landslide or triggering factor) I S H WHERE, WHEN - Elements at risk - Temporal-spatial probability - Vulnerability WHERE, WHEN, I S HR WHAT, HOW MUCH
  29. 29. I S H R WHERE
  30. 30. Type of Zoning : our work at University of Trento I S H
  31. 31. I •  LOCATION •  CLASSIFICATION •  AREAL EXTENT AND VOLUME •  CREEPING ZONES •  STATE OF ACTIVITY
  32. 32. I Individuation of the area where first - failure phenomenon or landslide reactivation can occur
  33. 33. I Mapping of the creeping zone allows the identification of the possible landslide evolution zones
  34. 34. I SHALLOW LANDSLIDES
  35. 35. I I. VELOCITY II.  OLUME V III.  NERGY E DEBRIS-FLOW, SHALLOW LANDSLIDE WITH COARSE-GRAINED SOILS DEEP LANDSLIDE WITH FINE- GRAINED SOIL
  36. 36. I S Landslides Inventory
  37. 37. I S
  38. 38. I S H
  39. 39. I S H Intensity Duration Return Time Source Area Deposition Area
  40. 40. I S H PROBABILITYTHAT A PARTICULAR DANGER (THREAT) OCCURS WITHIN A GIVEN PERIOD OF TIME IN A GIVEN LOCATION Type of Landslide Frequency Triggering Magnitude/Intensity Propagation
  41. 41. I S H TYPE OF LANDSLIDE Frequency Triggering Intensity Propagation
  42. 42. I S H TYPE OF LANDSLIDE Frequency Triggering Intensity Propagation 3 different approaches for landslides Intensity assessment 1) HISTORICAL INFO, GEOLOGY AND TOPOGRAPHY Assess the relative intensity from the estimated Landslide volume and the expected landslide BASIC LEVEL velocity (qualitative) 2) SIMPLE MODELS INTERMEDIATE LEVEL Estimate expected or observing landslide velocity 3) NUMERICAL MODELS Calculate the kinetic energy (velocity) by means of ADVANCED LEVEL numerical models
  43. 43. I S H TYPE OF LANDSLIDE Frequency Triggering Intensity Propagation 1) HISTORICAL INFO, GEOLOGY AND TOPOGRAPHY Assess the relative intensity from the estimated Landslide volume and the expected landslide velocity (qualitative) BASIC LEVEL
  44. 44. I S H TYPE OF LANDSLIDE Frequency Triggering Intensity Propagation •  requency of landslide can be determined from: F BASIC LEVEL: •  HISTORICAL DATA INTERMEDIATE LEVEL: •  RELATIONS WITH TRIGGERING EVENT FREQUENCY (I.E. RAINFALL, EARTHQUAKE) ADVANCED LEVEL: •  RELATING THE INDICATORS OR REVEALING FACTORS OF SLOPE STABILITY CONDITION (I.E. WATER CONTENT, GROUNDWATER LEVEL, PORE-WATER PRESSURE) TO TRIGGERING FACTORS (RAINFALL)
  45. 45. I S H TYPE OF LANDSLIDE Frequency Triggering Intensity Propagation AN EXAMPLE OF APPROACH AT REGIONAL SCALE Definition of an INDEX OF SLIDE PRONE AREA IN Given by the ratio between the number of towns affected by landslides during an event NI and the total number of threatened towns in the study area NT IN = NI / NT Relative to a given return Time T [year] in order to define an annual frequency f [year -1]
  46. 46. I S H TYPE OF LANDSLIDE Frequency Triggering Intensity Propagation For example by the definition of Rainfall Intensity-Duration Thresholds, considering the rainfall that caused landslides in the past and – eventually – the cumulative antecedent rainfall that predisposed to failure condition
  47. 47. I S H Type of Landslide FREQUENCY Triggering Intensity Propagation & (BASIC LEVEL) (INTERMEDIATE LEVEL) Care should be taken in the evaluation of landslide frequencies -  ECAUSE THE HISTORICAL DATA COULD BE AFFECTED BY ERRORS B -  ECAUSE THE CONDITIONS RESPONSIBLE FOR A GIVEN LANDSLIDE B FREQUENCY IN THE PAST MAY NO LONGER EXIST
  48. 48. I S H Type of Landslide FREQUENCY Triggering Intensity Propagation INITIAL CONDITION (ANTECEDENT SOIL MOISTURE) WATER TABLE LEVEL RAINFALL (INTENSITY, DURATION, RETURN TIME) WATER CONTENT AND PORE-WATER PRESSURE PROFILE ADVENCED LEVEL
  49. 49. I S H Type of Landslide FREQUENCY Triggering Intensity Propagation WATER TABLE LEVEL SAFETY FACTORS FS<1 WATER CONTENT PROFILE ADVENCED LEVEL
  50. 50. I S H Type of Landslide FREQUENCY Triggering Intensity Propagation You can assess these relations considering: - different wet initial conditions (on the base of cumulative rainfall dropped before of the event) - the seasonal mean humidity conditions ADVENCED LEVEL
  51. 51. I S H Type of Landslide Frequency TRIGGERING Intensity Propagation  GEOLOGICAL, GEOMORPHOLOGICAL AND HIDROGEOLOGICAL INVESTIGATION AND STUDIES - thickness of soil cover - hydrogeological features  GEOTECHNICAL AND HYDROLOGICAL INVESTIGATION AND STUDIES - In situ investigation on the stratigraphic condition of soil cover -  aboratory investigation for mechanical L and hydraulic characterization of soil -  In situ measurements -
  52. 52. I S H Type of Landslide Frequency Triggering Intensity PROPAGATION Based on statistical relationship and/or expert opinion Modelling the physical process EMPIRICAL METHODS ANALYTICAL METHODS GEOMETRICAL GEOMORPHOLOGICAL SINGLE-BLOCK FLUID DYNAMICS APPROACH APPROACH MODEL MODEL
  53. 53. I S H Type of Landslide Frequency Triggering Intensity PROPAGATION Based on statistical relationship and/or expert opinion EMPIRICAL METHODS GEOMETRICAL APPROACH
  54. 54. I S H Type of Landslide Frequency Triggering Intensity PROPAGATION Modelling the physical process ANALYTICAL METHODS FLUID DYNAMICS MODEL
  55. 55. THE TYPE AND LEVEL OF DETAIL OF THE ZONING AND THE SCALE OF THE MAPS DEPENDS ON THE PURPOSE TO WHICH THE LANDSLIDE ZONING IS TO BE APPLIED AND A NUMBER OF OTHER FACTORS: 1) The stage of development of the land use zoning plan or engineering project 2) The classification, activity, volume or intensity of landsliding. Risk zoning is more likely to be required where the landslides are likely to travel rapidly and or have a high intensity. For these situations life loss is more likely 3) The founding available 4) The amount and quality of available information. Quantitative (Advanced) hazard and risk zoning cannot be performed where data are not available Key words:
  56. 56. RECOMMENDED TYPES AND LEVELS OF ZONING AND ZONING MAP SCALES RELATED TO LANDSLIDE ZONING PURPOSE INTERNATIONAL GUIDELINES (FELL ET AL., I S H R 2008)
  57. 57. BUT YOU MUST ALSO THINK THAT SOMETIMES ADVANCED METHOD COULD NOT BE BETTER THAN SIMPLIFIED METHOD WHEN A BIG NUMBER OF INFORMATION ARE AVAILABLE, BECAUSE OF: 1) The big variability of the soil, bedrock and so on (heterogeneity) 2) Uncertainties in the processes understanding 3) Uncertainties in the measurements 4) Representativity of site-measurements and laboratory tests at the investigated area (Hydraulic Retention function, Hydraulic Conductivity function, thickness of the cover, bedrock permeability, etc) 5) DEM resolution 6) The dominant role of some factors respect to the others ANYWAY, ALSO THE OPPOSITE COULD BE TRUE……..
  58. 58. AN EXAMPLE: THE SIMPLE SHALSTAB MODEL (MONTGOMERY AND DIETRICH, 1994) •  Shallow landslide can occurr only for saturation from below. •  Does not account for unsaturated flow dynamics and for the suction contribute on the shear-strength resistance •  Considers only the steady-state condition for the subsurface water flow •  Overland flow is neglected, but It should modify the boundary conditions, (e.g. the water level in a channel located at the toe of the hillslope) •  Does not account the effects due to boundary conditions.
  59. 59. K = saturated hydraulic conductivity sat Z = soil thick h = soil-water thick in steady-state condition € β = slope gradient € A = Upslope contributing area € € € h h T =K Z cos β Steady-state subsurface flow Q = K Z cos β b sin β = T b sin β sat sub sat Z Z Steady-state overland flow Q =ν⋅A sup WATER BALANCE IN STEADY-STATE CONDITION € € h h Q +Q =I⋅A ν ⋅ A+K b Z cos β sin β =I⋅A T b sin β = (I − ν ) A sup sub € sat Z Z h h q A T b sin β = q A €Z = Z T b sin β € FS = tan φ'  γ w h  € 1−  tan β  γ s Z  € € q= I −v Effective rainfall in steady-state condition €
  60. 60. •  PARALLEL ACTUAL INTENSITY EFFECTIVE INTENSITY GEOTOP RAINFALL RAINFALL •  CONVERGENT Ip reale Ip efficace GEOtop •  DIVERGENT Ip reale Ip efficace GEOtop

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