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Mam Tor Fieldclass Sunday 12th March
depart from Department at 8.45am Pick up Greenbank at 9am return
approx. 6pm (depending on traffic)
You will need: standard field gear
mapping board notebook compass-clinometer ruler stationary
camera? LUNCH
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Slope stability II
EOSC316 Engineering Geoscience
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Types of landslide
Rock failure failure plane pre-
determined
Soil failure failure plane along line
of max stress
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Types of landslide
Rock failure failure along pre-determined planes of
weakness Soil failure
failure along lines of max. stress frictional, cohesive =
rotational frictional, incohesive = planar
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Rotational landslip analysis
For undrained frictionless failure total stress analysis
For cohesive and frictional failure method of slices Bishops
conventional method (can take into
account pore water pressure)
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Rotational slip
total stress analysis or u = 0
strength parameters are those of undrained soil
whereF = restraining moment
disturbing moment
C = cohesive strength (Pa)r = slip circle radius (m)= slip
sector in radiansW = weight of sliding sector (N)e = eccentricity
of sliding sector (m)
WeCrF
2
=
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Method of slices
Swedish circle method
For use with cohesive and frictional soils
+= n
n
nn
T
NCrF
1
1tan
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Effect of a tension crack
Reduces the angle of the sliding sector
Height of tension crack:
For frictionless soil
Chc
2=
C = cohesive strength (Pa)= unit weight of soil (N m-3) =
friction angle
+=
245tan2
Chc
Cohesive and frictional soil
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Location of slip circle centre
No simple way trial and error
F more sensitive to horizontal movements than vertical
movements
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Effective stress analysis
GWL
hP = h x f w
L
r
+= n
n
nnfn
T
LPNCrF
1
1tan)(
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Other methods of analysis
Taylors stability analysis used for frictional and cohesive
soils uses a dimensionless number to iterate
towards a solution Bishops method
effect of forces on each side of slice considered
iterative method
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Landslip monitoring
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Flowslides
Soil, clay, rock debris may behave like liquid; water content is
> liquid limit flowslide
Flowslides are extremely mobile e.g. Yungay, Peru, 1970
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Mt. Huascaran, Peru, 1970
earthquake triggered flowslide
hit towns of Yungayand Ranrahirca, 18 km away, at around 150
km/hr
Yungay completely buried, 66,000 dead
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Flowslide, Slumgullion, Colorado
National natural landslide laboratory
Major slip ~3500 years ago, present slip ~1000 years ago
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The Mam Tor head scar looking west
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Mam Tor landslide
Occurred due to glacially oversteepenedslopes
Age ~3600 years, from radiocarbon dating of tree remains
recovered from boreholes
~300 m wide and ~1000 m long Upper part
multiple rotation landslide Lower part
debris flow
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Cross-section through the Mam Tor landslip
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Geological map and movements at each station- 1996 to 2002
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Correlation of movements with rainfall
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An analogue for sedimentation in half-graben.
Derbyshire County Council is the transportation agent!
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Mam Tor references
Skempton, A.W. et al., 1989, The MamTor landslide, North
Derbyshire, Phil. Trans. Royal Soc. Lond. 329, 503-547
Rutter, E.H. et al., 2003, Strain displacements in the Mam Tor
landslip, Derbyshire, England, J. Geol. Soc. Lond.160, 735-744.
