Download - S2 Geo 1 Landslide Mechanism
Contents/ syllaby
• Introduction (Definition, Scope of study, Objective of study) – First week
• Rock mass classification & index properties (week 2 – 4)
• Rock strength and Failure criteria (week 5 – 6)
• Initial Stress & the measurement ( wee8 – 9)
• Planes of weakness in rock or rock discontinuity (week 10)
• Rock deformability (week 11)
• Applied rock mechanics ;– Rock slope engineering (week 12)
– Foundation Engineering (week 13)
– Underground excavation (week 14)
ROCK SLOPE STABILITY
(Teuku Faisal Fathani)
References:
- Introduction to Rock Mechanics (Goodman,
R.E., 1980)
- Rock Slope Stability (Giani, G.P., 1992)
- Rocks and Rocks Minerals (Dietrich, R.V.,
1979)
Topics
1. Landslide mechanism and causes
2. Rock strength
3. Rock slope engineering
4. Shear strength and failure criteria
5. Rock slope stability
6. Peak ground acceleration
7. Movement prediction
Mechanism and Causes of
Landslides
Landslide blocked both the river stream and the highway.
Jizukiyama
Landslide,
Japan
Many houses were
buried by the slide.
Sueling Landslide
Cibangkong Landslide, Banyumas Province
Type of Movement Type of Material
Bedrock Engineering soils
Predominantly coarse Predominantly fine
Falls Rockfall Debris fall Earth fall
Topples Rock topple Debris topple Earth topple
Slides: Rotational
A few units Rock slump Debris slump Earth slump
Slides: Translational
A few units Rock block slide Debris block slide Earth block slide
Many units Rock slide Debris slide Earth slide
Lateral spreads Rock spread Debris spread Earth spread
Flows Rock flow (deep
creep)
Debris flow (soil
creep)
Earth flow (soil
creep)
Complex Combination of two or more principal types of movements
Geological formations are subdivided into bedrock, debris soil and earth
soil. Slope movements were classified by Varnes (1978) into 18 types.
The abbreviated classification of slope movements:
Type of
Movement
Identification Type of Movement Identification
Rockfall Debris slide
Rock topple Debris spread
Rock slump Debris flow
Rock slide Earth fall
Rock spread Earth topple
Rock flow Earth slump
Complex Earth slide
Debris fall Earth spread
Debris topple Earth flow
Debris slump
Frequency of the Varnes classification movement types and identification
difficulty degree in the Italian geological environment (Carrara et al., 1985)
Slope movement types :
Large diffused slope; Average diffuse; Rare diffused
Easily identifiable slope; Difficult to identify; Unlikely identifiable
Rate Definition term
> 3 m/s Extremely rapid
> 3 m/min Very rapid
> 1.5 m/day Rapid
> 1.5 m/month Moderate
> 1.5 m/year Slow
> 0.006 m/year Very slow
< 0.006 m/year Extremely slow
Slope movement scale (after Varnes, 1978)
HEAVESLIDE
DRY
WET FAST
SLOW
FAST SLOW
Rock Slide
Landslide
Earth Flow
Mud Flow
Debris
FLOW
Carson and Kirkby (1972) proposed the classification of slope
movements based on water content of sliding mass and slope
movement velocity
Difference between landslide and slope failure
Landslides Slope Failures
Geology Occur in places with particular
geology or geological formation
Slightly related to geology
Soils Are mainly active on cohesive
soil such as slip surface
Frequently occur even in sandy
soils
Topography Occur on gentle slopes of 5° to
20°Frequently occur on the slopes
steeper than 30°
Situation of
activities
Continuous, or repetitive
occurrences
Occur suddenly
Moving velocity Low at 0.001 to 10 mm/day High speed > 100 mm/day
Masses Have little disturbed masses Have greatly disturbed mass
Provoking causes Greatly affected by groundwater Affected by rainfall intensity
Scale Have a large scale between 1
and 100 ha
Have a small scale. Average
volume is about 440 m3
Symptom Have cracks, depressions,
upheavals, groundwater
fluctuation, before occurrence
Have few symptoms and
suddenly slip down
Gradient 10° to 25° 35° to 60°
Some terms describing a landslide
(Cruden and Varnes, 1996)
Some terms describing a landslide
(Cruden and Varnes, 1996)
Causes of Landslide
• Rainfall or storm rainfall the rising of
groundwater level
• Construction works Earthwork, Cutting,
Filling, Tunnel construction,
• Reservoir induced landslide the rising and
drawdown of reservoir level
• Earthquake horizontal acceleration gx, gy
The main causative factors of Landslides
(Anagnostopoulos, 2005)
1. Climatic conditions
2. Topography
3. Lithology and distribution of soil and
rock formations (Geological Conditions)
4. Past and recent tectonic activity
(Seismicity)
5. Vegetation
6. Human activities
Rainfall – Storm Rainfall
• The magnitude of the absolute amount of annual
rainfall is not always related to the occurrence
rate of landslides
• Because the landslide occurrence related to
difference factors such as lithology-geology,
topography, vegetation, human interfere,
amount of rainfall vs duration of the event
A
ccum
ula
ted r
ain
fall
am
ount
Hourly r
ain
fall
am
ount
(in C
hoshi)
The n
um
ber
of
occurr
ence o
f la
ndslid
es
in c
liffs
Om
igaw
a-m
achi
Fig. 5.1.2 The Relationship between the Landslides in the Cliffs inOmigawa-machi
in Chiba Prefecture and the Rainfall Amount (Original by Hosono)
(The time when the Typhoon No. 25 hit in September 1971)
The relationship between landslides in the cliffs in
Omigawamachi-Chiba Prefecture and the rainfall amount
Accum
ula
ted r
ain
fall
am
ount
Landslid
es in
clif
fs
(S 42)1967
Hourly r
ain
fall
am
ount
Accum
ula
ted
rain
fall
am
ount
Landslid
es
in c
liffs
Hourly r
ain
fall
am
ount
Num
ber
of
occurr
ence
Fig. 5.1.3 The Relationship between the Rainfall Amount in City of Kobe and
the Time at which Landslides in the Cliffs Occurred (Original by Hosono)
The relationship between the rainfall amount in Kobe city and
the time at which landslides in the cliffs occurred
8th, 9th, 10th, 11th, 12th, 13th
September 1976
The Rainfall Amount in Ichinomiya
The landslide occurred in Nukiyama
Fig. 5.1.4 The Status of the Rainfall in Ichinomiya-machi in Hyogo Prefecture
Groundwater Level and Landslide
Movement
• Many reports presented about the correlation between
rainfall and the groundwater level in the landslide site,
and the relationship between the groundwater and
landslide displacement.
• Watari describes that there is a close relationship
between the water level of ponds and landslide
movement in Takizaka landslide (Fukushima Pref.)
• Taniguchi performed a soil mechanic analysis on the
groundwater level and the landslide movement velocity
in Kamiya landslide (Niigata Pref.).
Fig.5.1.6 The Relationship between the Daily Rainfall Amount and
the Displacement Velocity in Mt. Chausu (by Fukuoka)
The relationship between the daily rainfall amount and
displacement velocity in Mt. Chausu)
Fig.5.1.9 The Relationship between the Pore Water Pressure at the Sliding Surface or
Groundwater Level and the Velocity (by Fukuoka)
The relationship between pore water pressure at the sliding
surface or groundwater level and the velocity of landslide
Landslide due to construction works
• Recently, there are increasing cases of landslides in
mountainous areas, caused by large-scale cuttings and fillings
associated with construction of roads, tunnels, or large-scale
land developments.
• These landslides jeopardize execution of the project that has
caused the landslide, or oblige the project to be greatly
modified, or seriously damage, or threaten the safety of
houses and important facilities in the surroundings.
• Most of these landslides could have been avoided if a detailed
study had been done and appropriate preventive measures
based on the results of the detailed study had been taken
Road cutting
Human-induced landslide
Subsidence
Deformed sliding surface
Loosened zone
Case of A): Occurrence of
loosening and subsidence
Sliding surface with reduced stability
Loosened zone
Case of B): Loosening
Potential sliding surface
Transited sliding surface
Case of C): Transition of sliding surface, tunnel drilling too
close to the sliding surface
Fig.5.2.8 Tunnel Drilling beneath Sliding Surface
Tunnel Drilling beneath
Sliding Surface
Sliding cliff
Landslide mass Subsidence
Tunnel
Block
Sliding surface
Fig.5.2.9 Loosening by Tunnel Drilling and Occurrence of Landslide
Loosening by Tunnel Drilling and Occurrence of Landslide
Reservoir induced landslides
• The countermeasures of landslides around dam
reservoirs have been carried out to date, especially
after the occurrence of landslide at the Vaiont Dam in
Italy 1963 that resulted in 2,600 deaths
• The reservoir-induced landslides include those
occurring with the rise of reservoir level and those
occurring with rapid drawdown of the reservoir level
(Yoshimatsu, 1981).
Dam (Reservoir) construction Human-induced landslide
Landslide at A dam reservoir
Location : A dam, A1 area, Shikoku Island, Japan.
Geological feature:
Site investigation:
1. Tiltmeter
2. Piezometers installed in the boreholes
Weathered slate and schalstein (Mesozoic & Paleozoic)
Fracture-zone type landslide
Reservoir level, tiltmeter fluctuation and rainfall
at A dam area
Precipitation (mm)
Cracks found
Typhoon
No. 13
Typhoon
No. 19
1 m/day
1 m/day
0.5 m/day
Rese
rvo
ir level (m
)
210
200
190
180
170
160
150
Tiltm
ete
r fl
uctu
ati
on
(sec
)
4/1 5/1 6/1 7/1 8/1 9/1Time
5040302010
50
0
-50
-100
1 c= 0 kN/m2 ; =34.25o
2 c= 5 kN/m2 ; =32.15o
3 c=11 kN/m2 ; =29.50o
4 c=15 kN/m2 ; =27.65o
5 c=20 kN/m2 ; =25.26o
6 c=25 kN/m2 ; =22.77o
7 c=30 kN/m2 ; =20.19o
8 c=62.54 kN/m2 ; =0o
FS change by the rising of reservoir level
0 10 20 30 40 50 60 70 80 90
Distance (m)
160
170
180
190
200
210
220
230
0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6
Safety factor
Res
erv
oir
lev
el (
m) a
V
III
II
I
IV
Sliding mass
Bedrock
875 61 2 3 4
I Low level
II Limiting level
III Normal level
IV Failure level
V Surcharge level
Distance (m)
Safety factor
Rese
rvo
ir level (m
)
40
60
80
100
120
140
160
180
0 20 40 60 80 100 120 140 160 180 200
Distance (m)
Re
se
rvo
ir le
ve
l (m
)
Landslide at E dam reservoir
c - tan
FS vs cc=20 kN/m2 ; =33.69o
c=30 kN/m2 ; =31.93o
c=40 kN/m2 ; =30.10o
c=42.1kN/m2 ; =29.71o
c=45 kN/m2 ; =29.16o
c=50 kN/m2 ; =28.20o
c=80 kN/m2 ; =22.05o
t=18 kN/m3
sub=8 kN/m3
Actual slip surface
1 2 3 45 6
7
1
2
3
4
5
6
7
3
1
2
45
6
7
20
30
40
50
60
70
80
0.40 0.45 0.50 0.55 0.60 0.65 0.70
tan
Co
he
sio
n, c
(k
N/m
2)
7
654
2
1
3
0.96
0.97
0.98
0.99
1.00
20 30 40 50 60 70 80
Cohesion, c (kN/m2)
Sa
fety
Fa
cto
r
Chi-chi Earthquake (1999)
• The Chi-chi Earthquake (Sept 21st, 1999), the biggest quake
on Taiwan in this century, has a Richter scale magnitude of
7.6. The peak ground acceleration greater than 1g was
recorded. Nearly 2400 people were dead and more than
10,000 were injured. Total damage 9,200 million USD.
• Across the Central Mountain Range of Taiwan, at least 7000
landslides hit an area of several thousand square kilometers.
There were 16 places where individual landslide area
exceeds 10 ha. There were two gigantic landslides of an order
of magnitude of 108 m3, at Tsaoling and Chiufengershan.
Earthquake induced landslides
E-W
-1000
-800
-600
-400
-200
0
200
400
600
800
1000
0 20 40 60 80
Time(Second)
Acceleration(gal)
Earthquake magnitude = 7.6 R or 7.3 R (BMG Taiwan)
Epicenter depth = 7.5 km
The maximum acceleration of earthquake motion = 989gal(s)
(near Sun Moon Lake of a 魚池 basin, EW ingredient
Maximum speed, the shake is observed for a long time very
greatly with about 40 seconds,
Prof. Mori (DPRI-Kyoto Univ):
車籠埔 (Che-lum) Fault moved in
the direction of north and south in
about 25 seconds as a mechanism
of this earthquake covering the full
length of about 60 km
Damage of 石岡 Dam on September 21st 1999
Damage in mountain slope
Tsaoling Landslide
Induced by 1999 Chi-
chi Earthquake,
Taiwan
Volume: 1.4 x 108 m3
Affected area: 698 ha
Total length: 4 km
Source area:
Length: 1.5 km
Width: 2 km
Depth: < 200 m
Destruction of 5
houses, resulting in 29
deaths
Chiufengershan Landslide
Induced by 1999 Chi-
chi Earthquake
Volume : 3 x 107 m3
Affected area : 180 ha
Total length : 1.2 km
Width: 1.1 km
Average depth:
30~50m
Destruction of 21
houses, resulting in 41
deaths.
The landslide blocked
the river along 1 km,
and 2 small lakes
have been formed at
the upstream.
気象庁:平成16年(2004年)新潟県中越地震についての報道発表資料(2004年10月23日19時10分発表)
Chuetsu Earthquake, Niigata Pref, Japan(M=6.8)
Landslides induced by the Chuetsu Earthquake, Japan
Landslide dam caused by
the Chetsu Earthquake
ランドスライドダムを形成した地すべり
梶金地すべり
More than 150 events of landslides occurred with various
dimension and mechanism in response to Bantul
earthquake May 27, 2006
Aims:
Most of the landslide susceptible areas were formed by
steep volcanic rocks such as interbeded tuff sandstone –
pumice breccia and andesitic breccia.
• Addresses factors controlling the occurrence and
mechanism of landslide
• Potential impact to the safety of surrounding
environment (empirical analysis)
Bantul Earthquake (2006)