lec 04 slope stability -...

CIE3032 지반공학및실험 lecture 04 slope stability 1

LECTURE 04

Slope stability

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Slopes

Types of slopes: natural vs. man-madeMan-made slopes: Cut / Engineered slopes

Types of slopes failureFallToppleSlideSpreadFlow

CIE3032 지반공학및실험 lecture 04 slope stability 3

Slopes

Fall: Sudden detachment of soil and/or rock fragments that fall down a slope / typically occurs in rock slopes

Topple: Forward rotation of soil and/or rock mass / also common in rock slopes

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Slopes

Slide: Downward movement of a soil mass occurring on a surface of rupture (often denoted as a failure surface) representative case of slope failure will be covered in the lecture

CIE3032 지반공학및실험 lecture 04 slope stability 5

Slopes

Spread: A form of slide by translation. Sudden movement of water bearing seams of sands or silts. Often occurs during earthquakes for shallow slopes (under liquefaction)

Flow: Downward movement of soil mass similar to a viscous fluid. Occurs under heavy rain or earthquakes (under liquefaction)

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A special interest: Debris flow 토석류

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A special interest: Debris flow 토석류

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A special interest: Debris flow 토석류 (우면산)

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A special interest: Debris flow 토석류 (우면산)

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Swedish circle

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Lecture outline

Definition of factor of safety – Limit equilibriumInfinite slopesPlanar failure surface – Culmann’s methodAnalysis of slopes with Circular failure surface

Slopes in homogeneous clay (Swedish circle method)Ordinary method of slicesModified Bishop method

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Factor of safety

The goal of analyzing a slope is to ensure that the slope is going to be safe enough given a certain configuration (soil properties, geometry, externally applied load, pore water pressure regime)

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Factor of safety

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Factor of safety

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Factor of safety

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Factor of safety

Also (potential) failure surface

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Infinite slopes - Dry

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Infinite slopes - Dry

If c’=0, sand will stand at an angle of repose equal to its friction angle sand will stand at an angle of repose equal to its friction angleIf > ϕ, will result in sliding until = ϕ

′ ′ ′

/

′ ′

H

’v=zcosNormal and tangential components of ’v(’v)n=zcos2(’v)t=zcos2

’v

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Infinite slopes - Submerged

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Infinite slopes – Seepage parallel to slope surface, with phreatic line at slope surface

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Infinite slopes – Seepage parallel to slope surface, with phreatic line at slope surface

Equipotential line

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Infinite slopes – Seepage parallel to slope surface, with phreatic line at slope surface

Uside = Uleft – Uright = 0Ubase = wHcos2(L/cos )

= wHLcos

Hcos

Hcos2

CIE3032 지반공학및실험 lecture 04 slope stability 23

Infinite slopes – Seepage parallel to slope surface, with phreatic line at slope surface

Teq

Ubase

N’

N

W

FS = N’tan/Teq

Teq = Wsin = HLsatsin N = Wcos = HLsatcos N’ = Wcos - Ubase

=HLsatcos - HL wcos =HL ’cos

′

′

FS = ’tan/

= Wsin /(L/cos )= satHsin cos ’ = (-pore pressure)

=(satHcos2 - H wcos2)=(’Hcos2)

′

′

′

′

′

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Finite slope with Plane failure surfaces– Culmann’s method

W=

CIE3032 지반공학및실험 lecture 04 slope stability 25

Finite slope with Plane failure surfaces– Culmann’s method

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Finite slope with Plane failure surfaces– Culmann’s method

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Finite slope with Plane failure surfaces– Culmann’s method

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Finite slope with Plane failure surfaces– Culmann’s method

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Finite slope with Plane failure surfaces– Culmann’s method

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Finite slope with circular failure surface