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drwzwy::2010 LANDSLIDE Assoc. Prof. Dr. Wan Zuhairi Yaacob Geologi, UKM 2/12/2010

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Page 1: WEATHERING AND MASS WASTINGpkukmweb.ukm.my/zuhairi/Pengajaran/intranet/stag... · •Kestabilan cerun •Kegagalan cerun •Susutan darat •Amblesan •Gelinciran tanah drwzwy::2010

drwzwy::2010

LANDSLIDE

Assoc. Prof. Dr. Wan Zuhairi Yaacob

Geologi, UKM

2/12/2010

Page 2: WEATHERING AND MASS WASTINGpkukmweb.ukm.my/zuhairi/Pengajaran/intranet/stag... · •Kestabilan cerun •Kegagalan cerun •Susutan darat •Amblesan •Gelinciran tanah drwzwy::2010

drwzwy::2010

Tanah Runtuh

• Tanah runtuh berlaku apabila batu,

tanah atau ketulan bongkah tanah yang

besar digerakkan menuruni cerun oleh

sesuatu daya

2/12/2010

Page 3: WEATHERING AND MASS WASTINGpkukmweb.ukm.my/zuhairi/Pengajaran/intranet/stag... · •Kestabilan cerun •Kegagalan cerun •Susutan darat •Amblesan •Gelinciran tanah drwzwy::2010

Istilah

• Tanah Runtuh

• Kestabilan cerun

• Kegagalan cerun

• Susutan darat

• Amblesan

• Gelinciran tanah

drwzwy::2010

• Landslide

• Slope stability

• Slope instability

• Mass movement

• Mass wasting

• Landslip

2/12/2010

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drwzwy::2010

Classification of type of landslip (Varnes, 1978)

Slump

Curve slip surface

Planar slip surface

2/12/2010

soil

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drwzwy::2010

Saturated materials

2/12/2010

Liquefaction (quake)

Page 6: WEATHERING AND MASS WASTINGpkukmweb.ukm.my/zuhairi/Pengajaran/intranet/stag... · •Kestabilan cerun •Kegagalan cerun •Susutan darat •Amblesan •Gelinciran tanah drwzwy::2010

drwzwy::2010

Slumps Rock Slides

2/12/2010

Page 7: WEATHERING AND MASS WASTINGpkukmweb.ukm.my/zuhairi/Pengajaran/intranet/stag... · •Kestabilan cerun •Kegagalan cerun •Susutan darat •Amblesan •Gelinciran tanah drwzwy::2010

drwzwy::2010

Complex

2/12/2010

Page 8: WEATHERING AND MASS WASTINGpkukmweb.ukm.my/zuhairi/Pengajaran/intranet/stag... · •Kestabilan cerun •Kegagalan cerun •Susutan darat •Amblesan •Gelinciran tanah drwzwy::2010

drwzwy::2010

• A SLOW downhill

movement of soil.

Rayapan / Creep

2/12/2010

Page 9: WEATHERING AND MASS WASTINGpkukmweb.ukm.my/zuhairi/Pengajaran/intranet/stag... · •Kestabilan cerun •Kegagalan cerun •Susutan darat •Amblesan •Gelinciran tanah drwzwy::2010

drwzwy::2010

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

2/12/2010

Page 10: WEATHERING AND MASS WASTINGpkukmweb.ukm.my/zuhairi/Pengajaran/intranet/stag... · •Kestabilan cerun •Kegagalan cerun •Susutan darat •Amblesan •Gelinciran tanah drwzwy::2010

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

drwzwy::2010

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

Page 13: WEATHERING AND MASS WASTINGpkukmweb.ukm.my/zuhairi/Pengajaran/intranet/stag... · •Kestabilan cerun •Kegagalan cerun •Susutan darat •Amblesan •Gelinciran tanah drwzwy::2010

Slope angle

drwzwy::2010

= Tangent (rise/run)

2/12/2010

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drwzwy::2010

Slope increases; driving force increases

Landslide is frequent on steep slopes

2/12/2010

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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

drwzwy::20102/12/2010

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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

drwzwy::20102/12/2010

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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

drwzwy::20102/12/2010

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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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drwzwy::20102/12/2010

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Ampang, Selangor

(Perbandaran & Landslide)

drwzwy::20102/12/2010

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Bukit Antarabangsa

drwzwy::2010

“3 million dollar house with 10 million dollar view”

2/12/2010

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drwzwy::2010

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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drwzwy::2010

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

Page 27: WEATHERING AND MASS WASTINGpkukmweb.ukm.my/zuhairi/Pengajaran/intranet/stag... · •Kestabilan cerun •Kegagalan cerun •Susutan darat •Amblesan •Gelinciran tanah drwzwy::2010

Vaiont Dam, Italy

drwzwy::20102/12/2010

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drwzwy::2010

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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drwzwy::2010

A

B

2/12/2010

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drwzwy::2010

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)

drwzwy::20102/12/2010

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drwzwy::2010

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

Page 36: WEATHERING AND MASS WASTINGpkukmweb.ukm.my/zuhairi/Pengajaran/intranet/stag... · •Kestabilan cerun •Kegagalan cerun •Susutan darat •Amblesan •Gelinciran tanah drwzwy::2010

drwzwy::2010

• 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

drwzwy::20102/12/2010

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drwzwy::20102/12/2010

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Subsidence

• Sinkholes

• Coal mining and subsidence

• Groundwater extraction and

subsidence

• Earthquake and subsidence

• Limestone (karst) and subsidence

drwzwy::20102/12/2010

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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

2/12/2010 drwzwy::2010

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Sinkhole – aerial view

Limestone (karst) and subsidence

2/12/2010 drwzwy::2010