#10 - landslide - universiti kebangsaan · pdf fileengineering spec –diverted stream ......
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drwzwy::2010
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
drwzwy::2010
• 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
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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
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
22
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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
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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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http://www.uwsp.edu/geo/projects/geoweb/participants/Dutch/VTrips/Vaiont.HTM
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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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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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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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