Landslide Mechanisms and Processes: Understanding Slope Failures

Landslide Mechanism

This document provides a comprehensive analysis of landslide mechanisms, covering the fundamental principles, triggering factors, and classification of slope failures. It explores the complex interactions between geological, hydrological, and geotechnical factors that contribute to slope instability. Key topics include the role of groundwater, soil and rock behavior, shear strength reduction, and external influences such as seismic activity and human interventions.

In addition to theoretical insights, the document presents case studies and analytical approaches used to assess landslide hazards, including numerical modeling, remote sensing techniques, and geotechnical investigations. Understanding landslide mechanisms is crucial for designing effective mitigation measures, ensuring infrastructure resilience, and enhancing disaster risk management strategies.

This resource is essential for geotechnical engineers, researchers, and professionals involved in slope stability analysis, infrastructure development, and environmental risk assessment.

#LandslideMechanism #GeotechnicalEngineering #SlopeStability #engineering #rockslopestability #rockmechanics

1. 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)

2. 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)

3. 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

4. Mechanism and Causes of
Landslides

5. Landslide blocked both the river stream and the highway.

6. Jizukiyama
Landslide,
Japan
Many houses were
buried by the slide.

7. Sueling Landslide

8. Cibangkong Landslide, Banyumas Province

11. Type of Movement Type of Material
Bedrock Engineering soils
Predominantly coarsePredominantly 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 slideDebris 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:

12. Type of
Movement
IdentificationType 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

13. 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)

14. HEAVE
SLIDE
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 contentof sliding mass and slope
movement velocity

15. 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 velocityLow at 0.001 to 10 mm/day High speed > 100 mm/day
Masses Have little disturbed massesHave greatly disturbed mass
Provoking causesGreatly affected by groundwaterAffected by rainfall intensity
Scale Have a large scale between 1
and 100 ha
Have a small scale. Average
volume is about 440 m
3
Symptom Have cracks, depressions,
upheavals, groundwater
fluctuation, before occurrence
Have few symptoms and
suddenly slip down
Gradient 10°to 25° 35°to 60°

16. Some terms describing a landslide
(Cruden and Varnes, 1996)

17. Some terms describing a landslide
(Cruden and Varnes, 1996)

18. 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 g
x, g
y

19. 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

20. Rainfall –Storm Rainfall
•The magnitude of the absolute amount of annual
rainfall is not always relatedto 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

21. Accumulated rainfall amount

Hourly rainfall amount

(in Choshi)

The number of occurrence of landslides in cliffs

Omigawa
-
machi

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

22. Accumulated rainfall amount

Landslides in cliffs

（S 42）1967
Hourly rainfall amount

Accumulated
rainfall amount

Landslides in cliffs

Hourly rainfall amount

Number of occurrence

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

23. 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

24. Groundwater Level and Landslide
Movement
•Many reports presented about the correlation between
rainfalland the groundwater levelin the landslide site,
and the relationship between the groundwaterand
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.).

25. 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)

26. 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

27. 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

29. Road cutting
Human-induced landslide

32. 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

33. 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

34. 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).

35. Dam (Reservoir) construction Human-induced
landslide

37. 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

38. 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
Reservoir level (m)
210
200
190
180
170
160
150
Tiltmeter
fluctuation (sec)
4/1 5/1 6/1 7/1 8/1 9/1
Time
50
40
30
20
10
50
0
-50
-100

39. 1 c= 0 kN/m
2
; =34.25
o
2 c= 5 kN/m
2
; =32.15
o
3 c=11 kN/m
2
; =29.50
o
4 c=15 kN/m2 ; =27.65
o
5 c=20 kN/m2 ; =25.26
o
6 c=25 kN/m2 ; =22.77
o
7 c=30 kN/m2 ; =20.19
o
8 c=62.54 kN/m2 ; =0
o
FS change by the rising of reservoir level0102030405060708090
Distance (m) 160
170
180
190
200
210
220
230
0.70.80.91.01.11.21.31.41.51.6
Safety factor
Reservoir level (m)
a
V
III
II
I
IV
Sliding
mass
Bedrock
87561234
I Low level
IILimiting level
IIINormal level
IVFailure level
VSurcharge level
Distance (m)
Safety factor
Reservoir level (m)

40. 40
60
80
100
120
140
160
180
020406080100120140160180200
Distance (m)
Reservoir level (m) Landslide at E dam reservoir
c-tan
FSvs c
c=20 kN/m
2
; =33.69
o
c=30 kN/m
2
; =31.93
o
c=40 kN/m
2
; =30.10
o
c=42.1kN/m
2
; =29.71
o
c=45kN/m
2
; =29.16
o
c=50kN/m
2
; =28.20
o
c=80 kN/m
2
; =22.05
o

t=18 kN/m
3

sub=8 kN/m
3
Actual slip surface
1
2
3
4
5
6
7
1
2
3
4
5
6
73
1
2
4
5
6
7
20
30
40
50
60
70
80
0.400.450.500.550.600.650.70
tan 
Cohesion, c (kN/m
2
) 7
6
54
2
1
3
0.96
0.97
0.98
0.99
1.00
20304050607080
Cohesion, c (kN/m
2
)
Safety Factor

42. Chi-chi Earthquake (1999)
•The Chi-chi Earthquake (Sept 21
st,
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 10
8
m
3
, at Tsaolingand Chiufengershan.
Earthquake induced landslides

43. 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,

44. Prof. Mori (DPRI-Kyoto Univ):
車籠埔(Che-lum) Faultmoved 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

45. Damage of 石岡Dam on September 21
st
1999

46. Damage in mountain slope

47. Tsaoling Landslide
Induced by 1999 Chi-
chi Earthquake,
Taiwan
Volume: 1.4x 10
8
m
3
Affected area: 698ha
Total length: 4km
Source area:
Length: 1.5 km
Width: 2km
Depth: < 200 m
Destruction of 5
houses,resulting in 29
deaths

49. ChiufengershanLandslide
Induced by 1999 Chi-
chi Earthquake
Volume : 3x 10
7
m
3
Affected area : 180ha
Total length : 1.2km
Width: 1.1km
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.

50. 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)

51. Landslides induced by the Chuetsu Earthquake, Japan

52. Landslide dam caused by
the Chetsu Earthquake

54. ランドスライドダム
を形成した地すべり
梶金地すべり

56. 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)