5 Slope Stability
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Transcript of 5 Slope Stability
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Chapter 5
Slope Stability
FKAAS, UTHM
Dr. CM Chan
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5.1 Natural and artificial slopes
(Whitlow 2001)
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5.2 Soil moements ! Slope insta"ilit#
Falls
Topples
Slides- rotational, compound, translational
Lateral spreads
Flows
Complex or compound failure
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5.2.1 $#pes of soil moements
(Whitlow 2001)
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5.% Causes of insta"ilit#
Main categories-te causes of slope insta!ilit"#
$ %round conditions- weatered, fissures, etc&
$ %eomorpological processes- tectonic
acti'ities, wa'e erosion, etc&
$ ("sical processes- rainfall, tidal effects,etc&
$ Man-madeprocesses- exca'ation, drawdown
of water le'el )reser'oirs*, mining, +uarr"ing,
etc&
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Commoncauses of slope insta!ilit"#
$ eateringeffect
$ Canges of slope geometr"
$ ecrease in effecti'e stressof soil mass
$ .xcess loading)e+ui'alent to increase in
eigt of slope*
$ (oor design and/or construction- e&g&exca'ation near toe of existing slope
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5.& Slope sta"ilit# anal#sis
Metods of anal"sis#
$ 0nfinite slope metod- plane translational
slide
$ .ffecti'e and total stress approac )usuall"
u1 2o*
$ Fellenius or Swedis or ordinar" slice
metod
$ Metod of slices )effecti'e stress*- 3isop4s
metod, 3isop4s modified metod
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$ Ta"lor4s metod- undrained anal"sis
$ 3isop-Morgenstern4s metod
$ 5an!u4s metod- non-circular slip surfaces
$ edge metod- single plane
Focus:
$ Fellenius or Swedish or ordinary slice method
$ Taylors method- undrained analysis
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5.5 'actor of safet# ('S)
6elies on sound engineering 7udgement,
consideration of 'arious contri!uting factors and
appropriate metod of anal"sis&
Factors to !e considered#
$ Conse+uencesof failure
$ Confidencein te a'aila!le information and
data
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Higfactor of safet" )FS*#$ ris8 of loss of li'es and ad7acent structures-
ultimate limit state
$ possi!ilit" tat slope could !e prone tpdeformations wic could affect ad7acent
structures, e'en if it as sufficient sta!ilit"-
ser'ice limit state
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Lowerfactor of safet" )FS*#
$ period of exposure to factors causing
insta!ilit" is sort- e&g& temporar" wor8s
$ do notaffect li'es or structures
$ localised- simple remedial measures )wen
re+uired*
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9arious factors to !e considered in coosinga
suita!le FS#
$ (ast or local experience- presence or pre-
existing slip planes, future canges to soil
profile, water ta!le le'els, etc&
$ Complexit" of ground conditions
$ ata from site in'estigationreports
$ Confidence in design parameters)searstrengt, pore pressures, etc&*
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5. $a#lors method
6efers to Ta"lor4s cur'es )Ta"lor4s # undrained
anal"sis sta!ilit" cart*&
Ta"lor ):;, depends on slope inclination
angle, ?, and dept factor, , @ is dept of stiff
stratum&
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Ta"lor4s undrained anal"sis sta!ilit" cart&
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F 1 te lowest FS o!tained from a circular arc
anal"sisof a omogeneousslope wit undrainedsear strengt, cu, !ul8 unit weigt, , and eigt,
H u1 2o&
>s depends on te slope angle )or*, and
dept factor , were H )or @* 1 dept to stiff
stratum&
See Taylors curves (Fig. 12.10, pg.
!1"#arnes$.
%&le 12.' (#arnes$
30
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Hard la"er
.xample#
3ased on te a!o'e figure, @ 1 :B&2 m&
1 :B/:2 1 :&B
From Ta"lor4s cart, wit 1 :&B and ? 1 B2, terefore > 1 2&:B&>s 1 cu/ FH
FS 1 )
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5.* +rdinar# slice ! Swedish ! 'ellenius
method
Assumption# te inter-slice forcesare e+ualand
opposite- teir resultants are @ero&
.: 1 .B and E: 1 EB&
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6esol'ing te forces acting normalto te !ase
of eac slice# ) *cos - ul
*here,
u ) whw
hw) height to the water ta+le a+ove the
+ase o the slice or related to the
nearest euipotential line i a low netis drawn
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For a omogeneousslope wit c and constantalong te slip surface#
F 1 cLA3 tan)cos - ul*
sin*here,
$ *, and u are determined or each slice
and ta+ulated.$ can +e positive or negative.
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Te formula can !e rewritten as#
F 1 Gc4L )cos - rusec* tan4
sin
3" ta8ing ! 1 Lcos,
u 1 ru
Lcos
u 1 ru sec
L
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For a stead" state seepage troug slopes, te
pore pressure must !e ta8en into account-effecti'esear strengt parameters are used&
0f pore pressure is assumed to !e @ero#
F 1 GcL costan
sin
%&les .2a and .2+ (otes +y F /ing$
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.xample =&Ba (otes +y F /ing$
ivenTe slope and soil properties, as sown in
Fig& =&:IFind FS 'ia te Fellenius metod of slices for te
trial circle sown
:2;&Io
J
:2 m
6 1 : m
B&I m
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(rocedure#
:& Te slope was plotted to a con'enient scale&
B& For te assumed failure circle and te slices
selected, te widt of eac slice is measured as
B&I m&
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e&g& Te calculations for slice :are as follow#
: 1 )area* x )* 1 !/B
1 )B&I x : 1 :cos: 1 =
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Ta!le =&Ba