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Technical Committee 208 /
Comité technique 208
is also given as well as which factor(s)
F
i
has the most signifi-
cance on the result. The user can compare the ranking order and
can go back to the previous steps and change the weighting and
scoring factors, especially those with high effect on the ranking
R
i
, if necessary.
4 CLASSIFICATION OF MITIGATION MEASURES
The Safeland partner Studio Geotechnico Italiano S.r.l. (SGI)
prepared a "Compendium of tested and innovative structural,
non-structural and risk-transfer mitigation measures for differ-
ent landslide types" (SafeLand 1). This review was used a basis
for the selection and evaluation of the different mitigation
measures included in the toolbox for landslide hazard and risk
mitigation measures.
The classification of the mitigation measures was done in
terms of the components of a risk assessment (hazard, vulner-
ability and elements at risk). Table 1 presents this classification.
The classification system addresses three components of risk:
hazard, vulnerability and elements at risk, where risk R can be
expressed as:
R= H · C = H · V · E
where H is the hazard or the probability of occurrence of an ad-
verse event (landslide); C is the consequence(s); V is the vul-
nerability or the degree of loss of an element at risk for a given
hazard; and E are the elements at risk.
To reduce (or mitigate) the risk, one can reduce the hazard or
reduce the consequences (reduce the vulnerability or reduce the
exposure of the elements at risk).
Table 2. Classification of mitigation measures (structural measures on
top, non-structural measures on bottom)
Class
Component
of risk ad-
dressed
Brief description
Notes and other terms
used
Stabi-
liza-
tion
Hazard
(H)
Eng’g works to
reduce the land-
slide probability
of occurrence
Preventive, remedial,
hard, soft, active stabi-
lization.
Con-
trol
Vulnerabil-
ity(V)
(conse-
quence)
Eng’g works to
protect, reinforce,
isolate the ele-
ments at risk from
the landslide area
Preventive, hard, soft,
passive stabilization.
Avoid-
ance
Elements
(E)
(conse-
quence)
Temporary or
permanent reduc-
tion of exposure
w/ warning sys-
tems, evacuation/-
relocation, shelter-
ing, land-use
planning.
Reduction of the expo-
sure of the elements at
risk. Monitoring, early
warning systems and
civil protection proce-
dures, often tempo-
rary, selective avoid-
ance measures.
Tole-
rance
Elements(E)
(conse-
quence)
Awareness, accep-
tance and/or shar-
ing of risk
Indirect reduction of
the exposure of the
elements at risk.
Within the general domain of the structural mitigation meas-
ures classified above as “stabilization”, i.e. reduction of hazard,
it is possible to consider a further subdivision in relation to the
triggering factors and mechanisms that each measure addresses.
5 MITIGATION MEASURES CONSIDERED
The toolbox includes near 70 structural mitigation measures and
six non-structural mitigation measures. The structural measures
are divided into ten categories and belong to the class of meas-
ures either reducing hazard or reducing consequences. The
structural mitigation measures included are:
A
Structural measures reducing hazard
1
Surface protection and control of surface erosion
1.1 Hydro-seeding, turfing and trees/bushes
1.2 Fascines/brush
1.3 Geosynthetics
1.4 Substitution - drainage blanket
1.5 Beach replenishment, rip rap
1.6 Dentition
2
Modifying the slope geometry and/or mass distribution
2.1 Removal of (actual or potentially) unstable soil/rock mass
2.2 Removal of loose or potentially unstable blocks/boulders
2.3 Removal of material from driving area
2.4 Substitution in driving area with lightweight fill
2.5 Addition of material to the area maintaining stability
3
Modifying surface water regime - surface drainage
3.1 Surface drainage works (ditches, channels, pipe works)
3.2 Local re-grading to facilitate run-off
3.3 Sealing tension cracks
3.4 Impermeabilization (geo-membranes, impervious facing)
3.5 Vegetation - hydrological effect
3.6 Hydraulic control works (channel lining and check dams)
3.7 Diversion channels
4
Modifying groundwater regime - deep drainage
4.1 Shallow trenches filled with free-draining material
4.2 Deep trenches filled with free-draining material
4.3 Sub-horizontal drains (conventional drilling)
4.4 Sub-horizontal drains (directional drilling)
4.5 Wells
4.5.1 Small and medium dia. vertical wells (<800 mm)
4.5.1.1 Relief of artesian pressure
4.5.1.2 Under-drainage of perched aquifer
4.5.1.3 Pumps
4.5.1.4 Siphons
4.5.2 Medium diameter vertical wells (1200-1500 mm)
4.5.3 Large diameter vertical wells (>2000 mm)
4.5.4 Caissons (>5-6 m) with gravity drainage
4.6 Drainage tunnels, adits, galleries, with secondary drains
5
Modifying mechanical characteristics of unstable mass
5.1 Vegetation - mechanical effects
5.2 Substitution
5.3 Compaction from surface
5.4 Deep compaction (e.g. vibro-compaction)
5.5 Mechanical deep mixing with lime and/or cement
5.6 Low pressure grouting with chemical binder
5.7 Jet grouting
5.8 Modification of ground water chemistry
6
Transfer of loads to more competent strata
6.1 Counterfort drains (trench drains)
6.2 Piles
6.3 Barrettes (diaphragm walls)
6.4 Caissons - mechanical effects
6.5 Soil nailing
6.6 Dowels and harnessing
6.7 Rock bolting
6.8 Strand anchors
7
Retaining structures (to modify slope geometry and/or to
transfer stress to competent layer)
7.1 Reinforced soil structure
7.2 Gabion walls
7.3 Crib walls
7.4 Dry stack masonry walls
7.5 Mass concrete or masonry walls
7.6 Reinforced concrete stem walls
B
Structural measures reducing consequences
8
Deviating the path of landslide debris
8.1 Deflection structure
8.2 Debris flow/rockfall shed
9
Dissipating the energy of debris flows
9.1 Drop structure
9.2 Debris-restraining structure
9.3 Debris flow impediments
