Landslides
Landslides // Mass
Mass Wasting
Wasting
From
From My
My Homeowners
Homeowners Policy
Policy
(Why
(Whythis
thisis
isso
soimportant)
important)
Mass
Mass Wasting
Wasting
•• Any
Any downslope
downslope movement
movement of
of rock
rock
and
and soil
soil under
under the
the influence
influence of
of
gravity.
gravity.
•• "Landslide"
"Landslide"
•• "Rockslide"
"Rockslide" "Creep"
"Creep" "Rock
"Rock Fall"
Fall"
Landslide
Landslide Anatomy
Anatomy
Landslide sketch from the West Virginia Geological Survey
Important
Important Landslide
Landslide Facts
Facts
••
••
••
Most
Most are
are very
very slow
slow (inches
(inches per
per year)
year)
Most
Most occur
occur naturally
naturally
Homeowners
Homeowners insurance
insurance does
does not
not pay.
pay.
Landslide
Landslide Geography
Geography
••
••
••
••
Steep
SteepSlopes
Slopes
Slide-Prone
Slide-ProneSoils
Soils
High
HighPrecipitation
Precipitation
National
NationalLandslide
LandslideOverview
OverviewMap
Map
(connect)
Slide-Prone
Slide-Prone Area
Area Map
Map
Slide-prone area map by Peter Lessing, West Virginia Geological Survey
Angle
Angle of
of Repose
Repose
•• The
The maximum
maximum slope
slope at
at which
which loose,
loose,
cohesionless
cohesionless material
material is
is stable
stable
Angle
Angle of
of Repose
Repose Determined
Determined By
By
•• Particle
Particle size
size
(higher
(higher for
for large
large particles)
particles)
•• Particle
Particle shape
shape
(higher
(higher for
for angular
angular shapes)
shapes)
•• Shear
Shear strength
strength
(higher
(higher for
for high
high shear
shear strength)
strength)
Upsetting
Upsetting Stability
Stability
•• Increase
Increase the
the slope
slope
•• Decrease
Decrease the
the shear
shear strength
strength
•• Increase
Increase the
the effect
effect of
of gravity
gravity
Landslide
Landslide Triggers
Triggers
(A
(AFew
FewExamples)
Examples)
Type of Trigger
Natural
Human
Removal of
Support
Erosion
Excavation
Rainfall,
Snowmelt
Water disposal,
Improper grading
Addition of
Moisture
Removal of
Vegetation
Addition of
Weight
Oversteepening
Vibrations
Forest fires
Timbering
Volcanic ash,
Landslides, Snow
(Used like "removal
of support")
Earthquakes,
Thunder
Placement
of fill
Grading fill steeper
than its repose angle
Blasting, Heavy
equipment
Landslide
Landslide Considerations:
Considerations:
Gradient
Soil / Bedrock
Moisture
Vegetation
Support
Weight
Vibrations
Oversteepening
Risk starts at only 15o
Clay soils / shale bedrock are the worst
Pore pressure, Lubrication, Weight
Roots anchor soil, remove water
Must be maintained
Drives the slide, compression of substrate
Result in a loss of friction
Exceeding the angle of repose
What
What was
was the
the trigger?
trigger?
Who
Who is
is to
to blame?
blame?
#1
What
What was
was the
the trigger?
trigger?
Who
Who is
is to
to blame?
blame?
#2
What
What was
was the
the trigger?
trigger?
Who
Who is
is to
to blame?
blame?
#3
What
What was
was the
the trigger?
trigger?
Who
Who is
is to
to blame?
blame?
#4
What
What was
was the
the trigger?
trigger?
Who
Who is
is to
to blame?
blame?
#5
What
What was
was the
the trigger?
trigger?
Who
Who is
is to
to blame?
blame?
#6
Types
Types of
of Landslides
Landslides
Slump
Rotational Slide
Earthflow
Mudflow
Debris Flow / Avalanche
Rock Slide
Rock and soil moving as a unit over a
curved failure surface.
Similar to a slump, but the material breaks-up
and flows.
Much higher moisture content than an earthflow
- the material makes a "batter" with water.
A block of bedrock sliding down dip.
Block Glide
Creep
Complex
Landslide
Gradual downslope movement of rock and soil.
A combination of two different slide types.
Recognizing
Recognizing Problem
Problem Areas
Areas
••
••
••
••
••
••
••
••
••
••
••
••
Curved
Curvedtrees
trees
Stuck
Stuckwindows
windows
Stuck
Stuckdoors
doors
Leaning
Leaningwalls
walls
Plaster
Plastercracks
cracks
Foundation
Foundationcracks
cracks
Damaged
Damagedchimneys
chimneys
Leaning
Leaningpoles
poles
Scarps
Scarps
Toes
Toes
Seeps
Seeps
Pavement
Pavementdamage
damage
Before
Before buying
buying on
on aa hillside:
hillside:
••
••
••
••
••
••
Be
Be suspicious!
suspicious!
Check
Check target
target and
and adjacent
adjacent properties
properties
Some
Some problems
problems can
can be
be fixed
fixed
Fixes
Fixes are
are temporary
temporary and
and expensive
expensive
Get
Get expert
expert advice
advice
Soil
Soil Conservation
Conservation Service
Service //
Geological
Geological Survey
Survey
Landslide
Landslide Stabilization
Stabilization
••
••
Get
Getexpert
expertadvice
advice
Your
Yourefforts
effortswill
willprobably
probablygive
givetemporary
temporary relief
relief
••
••
••
••
••
••
Support
Supportthe
thebase
base
Anchor
Anchorthrough
throughslip
slipplane
plane
Lower
Lowerwater
watertable
table
Runoff
Runoffcontrol
control
Plant
Plantvegetation
vegetation
Excavate
Excavateslide
slidemass
mass
Landslide
Landslide Diagnosis
Diagnosis "A"
"A"
Landslide
Landslide Diagnosis
Diagnosis "B"
"B"
Landslide
Landslide Diagnosis
Diagnosis "C"
"C"
Landslide
Landslide Diagnosis
Diagnosis "D"
"D"