slope stability i eosc316 engineering geoscience
TRANSCRIPT
Slope stability I
EOSC316 Engineering Geoscience
Landslip trigger processes
• Water• Toe removal
– Natural– Artificial
• Head loading• Vibration
Folkestone Warren, Kent
• Toe erosion due to extension of harbour wall, 1905
• Since 1915 slide– mass concrete toe
weights– drainage adits
Mt. Huascaran, Peru, 1970
• earthquake triggered• hit towns of Yungay
and Ranrahirca, 18 km away, at around 150 km/hr
• Yungay completely buried, 66,000 dead
Types of landslide
• Rock failure– failure plane pre-
determined
• Soil failure– failure plane along line
of max stress
Rock failure
Planar translational slip in rock
shearfo rce
norm a l fo rce
w e igh t
• = angle of repose (= angle of friction)• Factor of safety = shear force at failure / shear force
Wedge failure in rock
angle of repose,
intersection of joint set
Factor of safety = tan / tan
Toppling failure, Masada, Israel
Effect of cohesive strength on bench height in rock
h
wcos wsin
a
a = h/sin
• Shear stress on sliding plane:
• Failure occurs when:
• Thus
hwC
hw
a
wC
sincos
sinsin
cos
Ch
w cossinsin2
tan2
cossin2
2hw
hh
Area of wedge
cossinsin
tan2
cossinsintan2
2max
22
Ch
or
Ch
h
Half dome, Yosemite Carrara marble quarries, Italy
Rock failure – remedial measures
Slope failure in ‘unconsolidated’ material
Planar versus rotational slip in unconsolidated material
• Planar slip– frictional– cohesionless– C = 0
• Rotational slip– frictional – cohesional– C ≠ 0
La Conchita, Santa Barbara, California, Spring 1995
Planar translational slip
shearfo rce
norm a l fo rce
w e igh t
• = angle of repose (= angle of friction)• Factor of safety = shear force at failure / shear force
Planar slip - analysis
angle of repose,
angular range where failure possible
intersection of joint set
Factor of safety = tan / tan
Planar slip in soils
GW L
Slipsurface
hw
h r
n = h /hw r
• Cohesionless soils (φ=0)
• Soils with cohesion (φ≠0)
tan
tanwnF
tan
tan
cossinw
r
n
h
CF