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drwzwy::2010
LANDSLIDE
Assoc. Prof. Dr. Wan Zuhairi Yaacob
Geologi, UKM
2/12/2010
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Tanah Runtuh
• Tanah runtuh berlaku apabila batu,
tanah atau ketulan bongkah tanah yang
besar digerakkan menuruni cerun oleh
sesuatu daya
2/12/2010
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Istilah
• Tanah Runtuh
• Kestabilan cerun
• Kegagalan cerun
• Susutan darat
• Amblesan
• Gelinciran tanah
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• Landslide
• Slope stability
• Slope instability
• Mass movement
• Mass wasting
• Landslip
2/12/2010
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Classification of type of landslip (Varnes, 1978)
Slump
Curve slip surface
Planar slip surface
2/12/2010
soil
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Saturated materials
2/12/2010
Liquefaction (quake)
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Slumps Rock Slides
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Complex
2/12/2010
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• A SLOW downhill
movement of soil.
Rayapan / Creep
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Debris flows or mudflows
• Commonly occur in volcanic areas, where they are called lahars.
• Mudflows– 50% silt & clay; 30% water
– Heavy rain
– follow existing channel
• Debris flow– larger particles & less water
– More viscous
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1. Forces on slopes• Driving forces (daya penyebab) – F1
– Move earth material down a slope
– Eg: weight of earth material
• Resisting forces (daya penahan) – F2
– Oppose such movement
– Eg: shear strength of slope material
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Factor of safety, FS (faktor keselamatan)
• Nisbah antara daya penahan
terhadap daya penyebab gelinciran
• FS > 1 (stabil) ; F2 > F1
• FS < 1 (gagal) ; F1 > F2
F1
F2
2/12/2010
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Factor of Safety, FS
drwzwy::2010
Fn
Fg
Fs
Gravity force
Shear force
(daya ricih)
Normal force
•The shear force acts to pull
the block down the plane.
•Normal force acts to
increase friction and stick
the block to the plane.
Fs; Fn
Fs = Fg Sin
Fn = Fg Cos
L
T
S – shear strength
A
2/12/2010
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FS
2/12/2010 drwzwy::2010
S = shear strength 9 x 104 N/m2 (lab test)
L = length of slip plane = 50 m
T = unit thickness = I m
Fg = area above slip plane x thickness x unit weight of slope
material
= 500 m2 x 1 m x 1.6 x 103 N/m3
= 8 x 106 N
= 30o
FS = 1.125
FS = 1. 25
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Slope angle
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= Tangent (rise/run)
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Slope increases; driving force increases
Landslide is frequent on steep slopes
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Vegetation on slope1. Provide cover that cushion
the impact of rain falling on
slope
2. Facilitating infiltration of
water
3. Retarding grain-by-grain
erosion
4. Root systems provide
cohesion to the slope
materials - adds to the shear
strength
5. Add weight to the slope (?)drwzwy::20102/12/2010
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Water
• Chemical weathering – reduce shear
strength
• Erosion ability of water
• Rise in pore water pressure; reduce the
shear strength (resisting force)
• Liquefaction of clay rich sediment
(quick/sensitive clay)- earthquake
triggered
• Seepage of water from artificial sources
– eg. St. Francis Dam
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Causes of landslide 1
1. External causes (Penyebab luaran)
– Increase the driving force (shear stress)
• eg. Loading of slope;
• steepening of slope – erosion / excavation
• Earthquake shocks or vibration
2. Internal causes (Penyebab dalaman)
– Reduce the shear strength
• eg. Increase pore water pressure
• Decrease in cohesion
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Causes of landslide 2
1. Natural causes
– rainfall and seepage; increase pore water
pressure
– vibrations caused by earthquakes;
– undercutting of cliffs and banks by waves or
river erosion; and
– volcanic eruptions.
2. Human causes – next page
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Human use and landslide
– Timber harvesting (deforestation /
penebangan hutan) & landslides
• removal of vegetation;
– Urbanization (perbandaran) & landslides
• interference with natural drainage;
• leaking pipes such as water
• modification of slopes by construction of roads,
railways, buildings, etc;
• overloading slopes;
– Mining (perlombongan) & landslides
• mining and quarrying activities
drwzwy::20102/12/2010
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2/12/2010 drwzwy::2010
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Ampang, Selangor
(Perbandaran & Landslide)
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Bukit Antarabangsa
drwzwy::2010
“3 million dollar house with 10 million dollar view”
2/12/2010
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Tragedi Tanah Runtuh di Taman Hill
View
• 20 Nov 2002
• 8 nyawa (built 1998)
• Gelinciran tanah kompleks
– Gelinciran putaran di bhg kepala
(atas/head)
– Gelinciran di tengah
– Aliran di kaki -- toe
• Panjang 200m, lebar 50m, 25000m3 bhn
2/12/2010
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• 30m ke selatan ; highland tower
– 11 Dis 1993
– 12 tingkat kondo
– 48 nyawa
– Saiz dan orientasi gelinciran sama
2/12/2010
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Punca:
– Hujan
– Zon gelinciran lama
– Bahan lemah
– Lineaman geologi (sesar)
– Bentuk lembangan (spoon shape)
– Gangguan cerun (abondoned project 1985)
– Rubble wall failure (13 walls)
• Large rocks bonded together with cement
• Not complied with basic engineering spec
– Diverted stream/covered – based on 1980 topographic map
2/12/2010
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Vaiont Dam, Italy
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Vaiont Dam Disaster, Italy
•October 9, 1963
•2600 terkorban
•Melibatkan empangan jenis thin
arch yang tertinggi di dunia (267m)
•238 Juta m3 batuan/debris
bergerak dengan kelajuan 95
km/jam
2/12/2010
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A
B
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The triggering mechanisms of the slide
• The creation of lake basin and the
variations in its level
• The presence of clay along the failure
surface
• The existence of ancient landslide
• The geological structure
• The seismicity of the area
2/12/2010
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Aberfan Disaster
(Mining and Landslide)
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The Aberfan Disaster
• 9:15am Friday October 21 1966
• Mining village of Aberfan, Merthyr Tydfil, South Wales, UK.
• Runtuhan sisa arang batu
• Runtuhan memusnahkan sebuah sekolah + 20 rumah:– Pantglas Junior School (age 7 to 10)
– All things bright and beautiful
– 144 maut: 116 adalah kanak-kanak (i.e. separuhkanak-kanak sekolah)
2/12/2010
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PUNCA KEJADIAN
• Underground spring under the tip
• Two days of heavy rainfall
• Half a million tons of coal waste
(overloading)
2/12/2010
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drwzwy::2010
SELEPAS KEJADIAN
• Mines and Quarry (Tips) Act (1969)
• Undang-undang berkaitan dengan
keselamatan buangan sisa lombong.
2/12/2010
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drwzwy::2010
Bournville Landslide, Wales,
United Kingdom
2/12/2010
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• Location
– the landslide is located at the Ebbw Fach valley
in South Wales, United Kingdom
– 40km from Cardiff City Centre
• South Wales Coalfield
– The South Wales Coalfield was one of the
major coalfields in the UK; (area = 2700 km2)
– The most exploited mineral in the area is coal;
mined extensively for the past 200 years
– 1870: 65% of Britain’s Coal production was
from South Wales
2/12/2010
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Minimizing the landslide
1. Identification of potential landslides
• Landslide Risk and Hazard
2. Prevention of landslide
• Drainage control
• Grading
• Slope supports
3. Landslide warning systems
4. Landslide correction
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Subsidence
• Sinkholes
• Coal mining and subsidence
• Groundwater extraction and
subsidence
• Earthquake and subsidence
• Limestone (karst) and subsidence
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Pemendapan tanah (land
subsidence) di San Joaquin
valley US. Sela masa 52 tahun
--- 30 feet (10 meters)
Excessive groundwater pumping
Groundwater extraction and subsidence
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Sinkhole – aerial view
Limestone (karst) and subsidence
2/12/2010 drwzwy::2010