14. 1) Which type of landslide?
DEPOSITION AREA
kinematic reconstruction
Type of material
15. 1) Which type of landslide?
DEPOSITION AREA
kinematic reconstruction
Type of material
16. 1) Which type of landslide?
DEPOSITION AREA
kinematic reconstruction
NEW
STREAM
PATH
17. 1) Which type of landslide?
VEGETATION – INDIRECT EVIDENCE
18.
19. 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
27. 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
28. 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)
29. 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
45. I S H
Intensity
Duration
Return Time
Source Area
Deposition Area
46. 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
47. I S H
TYPE OF LANDSLIDE Frequency Triggering
Intensity Propagation
48. 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
49. 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
50. 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)
51. 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]
52. 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
53. 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
54. 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
55. I S H
Type of Landslide FREQUENCY Triggering
Intensity Propagation
WATER TABLE LEVEL
SAFETY FACTORS
FS<1
WATER CONTENT PROFILE
ADVENCED LEVEL
56. 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
57. 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
-
58. 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
59. I S H
Type of Landslide Frequency Triggering
Intensity PROPAGATION
Based on statistical relationship and/or expert opinion
EMPIRICAL METHODS
GEOMETRICAL
APPROACH
60. I S H
Type of Landslide Frequency Triggering
Intensity PROPAGATION
Modelling the physical process
ANALYTICAL METHODS
FLUID DYNAMICS
MODEL
61. 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:
62. 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)
63. 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……..
64. 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.
65. 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
€
66. • PARALLEL
ACTUAL INTENSITY EFFECTIVE INTENSITY GEOTOP
RAINFALL
RAINFALL
• CONVERGENT
Ip reale Ip efficace GEOtop
• DIVERGENT
Ip reale Ip efficace GEOtop
