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#10 - LANDSLIDE

Assoc. Prof. Dr. Wan Zuhairi Yaacob

Geologi, UKM

10/20/2010 1

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Tanah Runtuh

• Tanah runtuh berlaku apabila batu,

tanah atau ketulan bongkah tanah yang

besar digerakkan menuruni cerun oleh

sesuatu daya

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VIDEO

Istilah tanah runtuh

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• Tanah runtuh (Landslide)

• Kestabilan cerun (Slope stability)

• Ketidakstabilan cerun (Slope instability)

• Kegagalan cerun (slope failure)

• Pergerakan jisim / susutan darat (Mass

movement / Mass wasting)

• Gelinciran tanah (Landslip)

• Subsidence

• Lubang benam (Sinkhole)

• Pemendapan tanah (Settlement)

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Kestabilan cerun

1. Peranan bahan bumi (earth material

type)

2. Daya-daya pada cerun (forces on

slopes)

3. Peranan sudut cerun dan topografi

4. Peranan cuaca dan tumbuhan

5. Peranan Air

6. Peranan Masa

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Classification of type of landslip (Varnes, 1978)

Slump

Curve slip surface

Planar slip surface10/20/2010

1. Peranan bahan bumi

Ro

tati

on

al

Tra

ns

lati

on

al

SL

IDE

ST

OP

PL

ES

FA

LL

S

ROCKS DEBRIS EARTH / SOIL

5

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Saturated materials

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Liquefaction (quake)

SP

RE

AD

SF

LO

WS

CO

MP

LE

X

Koluvium

6

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Pengaruh foliasi ke atas kestabilan cerun

2. Daya pada cerun

• Driving forces (daya penyebab) – F1

– Move earth material down a slope

– Eg: weight of earth material (w)

• 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

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w

8

Faktor keselamatan / kestabilan

Factor of Safety, FS

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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

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S = shear strength; 9 x 104 N/m2 (lab test)

L = length of slip plane = 50 m

T = unit thickness = I m

Fg = weight of slope material = 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

Faktor keselamatan / kestabilan

Factor of Safety, FS

(nilai terkecil FS yang

dibenarkan walaupun

melebihi 1.0)

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FS = 1. 25

FS = S.L.T / Fg Sin θ

Fg = S.L.T / FS.Sin θ

Fg = S.L.T / 1.25.Sin θ

•Menguranglkan beban batuan

pada cerun

•mengurangkan sudut cerun

Faktor keselamatan / kestabilan

Factor of Safety, FS

FS = 1.125

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3. Slope angle

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= Tangent (rise/run)

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Slope is ratio between the vertical rise

(height) and the horizontal run (length).

rise

run

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Slope increases; driving force increases

Landslide is frequent on steep slopes

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Cerun tambakan

13

4. 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::201010/20/2010 14

Bioengineering

Chrysopogon zizanioides

5. Peranan air1. Chemical weathering – reduce shear

strength (cth: batu kapur vs asid lemah)

2. Erosion ability of water

3. Rise in pore water pressure; reduce

the shear strength (resisting force) &

increase the weight (driving force)

4. Liquefaction of clay rich sediment

(quick/sensitive clay)- earthquake

triggered

5. Seepage of water from artificial

sources – eg. St. Francis Dam

– Perlarutan bahan simen dalam batuan

iaitu konglomerate & gypsum

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6. Peranan masa1. Daya-daya pada cerun

berubah mengikut masa

– Daya pencetus dan penghalang

berubah mengikut musim

– Cth: Musim hujan - frekuensi

tanah runtuh bertambah

2. Pengurangan daya

penghalang mengikut masa

– Luluhawa (mengurangkan

kejelekitan tanah – soil cohesion)

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fos

time

1

2

3

Failure !!

Causes of landslide 1

1. Real causes

– Pertambahan daya pencetus (driving

force) atau pengurangan daya

penghalang (resisting force)

2. Immediate causes

– Sesuatu faktor yang mencetus

kepada berlakunya landslide (trigger

factors)

– Gempa bumi, getaran dan

pertambahan air mendadak

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real cause : Bentonite layer

Immediate cause : heavy rains

real cause : steep slope / fractures

Immediate cause : vibrations

Causes of landslide 2

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

• Eg. Decrease in soil cohesion

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Causes of landslide 3

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

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2. 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

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Mining & overloading

deforestation

Ampang, Selangor

(Perbandaran & Landslide)

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Taman Bukit “Mewah”, KL

• Dec, 2008

• 5 nyawa

• 14 banglo mewah

• Kos pemulihan > 1

million RM ?10/20/2010 drwzwy::2010

Dari bawah

Back scar - grout

Dari puncak

Helicopter view

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Tragedi Tanah Runtuh di Taman Hill View

• 20 Nov 2002

• 8 nyawa

• Gelinciran tanah

kompleks

– Gelinciran putaran di

bhg kepala (atas/head)

– Gelinciran di tengah

– Aliran di kaki -- toe

• Panjang 200m, lebar 50m,

25000m3 bhn

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Built 1998

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• 30m ke selatan ;

highland tower

– 11 Dis 1993

– 12 tingkat kondo

– 48 nyawa

– Saiz dan orientasi

gelinciran sama

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Punca kejadian:

– Hujan lebat

– Zon gelinciran lama

– Bahan lemah (Batuan asalGRANIT)

– Lineaman geologi (sesar)

– Bentuk lembangan (spoon shape)

– Gangguan cerun (abandoned 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

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Loose soil

(sandy soil)

Tension gashes/crack

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

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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: fault, bedding, fractures

• The seismicity of the area

• Geology; limestone

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Dam

Reservoir

upstream

downstream

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http://www.uwsp.edu/geo/projects/geoweb/participants/Dutch/VTrips/Vaiont.HTM

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A

B

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a) Before ancient landslide

b) Movement down valley

c) New river channel

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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)

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PUNCA KEJADIAN

• Underground spring under the tip

• Two days of heavy rainfall

• Half a million tons of coal waste

(overloading)

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SELEPAS KEJADIAN

• Mines and Quarry (Tips) Act (1969)

• Undang-undang berkaitan dengan

keselamatan buangan sisa lombong.

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Bournville Landslide, Wales,

United Kingdom

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Geologi

– Usia Carboniferous

– Hughes Beds,

Brithdir Beds,

Rhonda Beds, Llynfi

Beds

– Terdiri dari batu

pasir, batu lumpur

dan batu lodak

– Endapan kuarterner:

glaciall till

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• Geology and structural geology

– interbedded sequences of sandstones,

siltstones, claystones dan coals

– crossed by some gentle folds and high angle

faults

• Strata dip in the direction of the slope

• Valley sides covered by thick deposits of

glacial and periglacial materials (loading)

• Average annual rainfall; 2-3 m

• extensive extraction of coals; caused

subsidences

• over-tipping of the valley sides by mine

wastes

• excavations for development at the lower

slopes10/20/2010

The instability produced from a combination of

several factors

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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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Ris

k a

naly

sis

Ris

k A

ss

es

sm

en

t

Ris

k M

an

ag

em

en

t

Identification of potential landslides

• Landslide Risk and Hazard

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Risk analysis

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Risk Assessment Risk Management

Landslide Maps

1. Landslide Inventory Map

2. Landslide Susceptibility Map

3. Landslide Hazard Map

4. Landslide Risk Map

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Prevention of landslide

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• Drainage control– Surface and subsurface

drainage control

– Keep water away from

the landslide area

– diversion trench : divert

groundwater flow

– Impermeable wall /

cutoff wall / soil-cement

/ plastic : prevent water

from entering the area

soil-cement

Prevention of landslide

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• Grading– Cut and fill

• Remove the upper part

of slope and place near

the base

– Benching

• Reduce the slope angle

• Collection for small

slides or falling rocks

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Prevention of landslide

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• Slope supports– Retaining walls

Concrete cribbing

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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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Canada’s Leaning tower

(the kissing silos)

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Sinkhole – aerial view

Limestone (karst) and subsidence

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Mengapa isu bukit antarabangsa belum dapat

diselesaikan ??

• 1. Sejarah pembangunan

– Pembangunan sebelum pengetahuan dan kesedaran

risiko tanah runtuh difahami

• 2. Keupayaan dan kekuatan politik pihak berkuasa

negeri dan tempatan

– Pencegahan, akta, peraturan dan sebagainya

• 3. Perubahan diperingkat komuniti yang berhadapan

masalah ini

– Kesedaran masyarakat

– Komuniti sbg agen perubahan

10/20/2010 drwzwy::2010

Prof Ibrahim Komoo

(SEADPRI)

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http://slopes.jkr.gov.my/

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TAMAT

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