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Mam Tor Fieldclass

Mam Tor Fieldclass. Thursday 17 th March depart from Department at 8.45am return approx. 6pm (depending on traffic) You will need: standard field gear mapping board notebook compass-clinometer ruler stationary camera? LUNCH. Slope stability II. EOSC316 Engineering Geoscience.

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Mam Tor Fieldclass

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  1. Mam Tor Fieldclass • Thursday 17th March • depart from Department at 8.45am • return approx. 6pm (depending on traffic) • You will need: • standard field gear • mapping board • notebook • compass-clinometer • ruler • stationary • camera? • LUNCH

  2. Slope stability II EOSC316 Engineering Geoscience

  3. Rock failure failure plane pre-determined Soil failure failure plane along line of max stress Types of landslide

  4. 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

  5. Rotational landslip analysis • For undrained frictionless failure • total stress analysis • For cohesive and frictional failure • method of slices • Bishop’s conventional method (can take into account pore water pressure)

  6. Rotational slip • total stress analysis or fu = 0 • strength parameters are those of undrained soil • where • F = restraining moment • disturbing moment • C = cohesive strength (Pa) • r = slip circle radius (m) • = slip sector in radians W = weight of sliding sector (N) e = eccentricity of sliding sector (m)

  7. Method of slices • Swedish circle method • For use with cohesive and frictional soils

  8. Effect of a tension crack • Reduces the angle of the sliding sector Height of tension crack: For frictionless soil Cohesive and frictional soil • C = cohesive strength (Pa) • = unit weight of soil (N m-3) f = friction angle

  9. Location of slip circle centre • No simple way – trial and error • F more sensitive to horizontal movements than vertical movements

  10. Effective stress analysis

  11. Other methods of analysis • Taylor’s stability analysis • used for frictional and cohesive soils • uses a dimensionless number to iterate towards a solution • Bishop’s method • effect of forces on each side of slice considered • iterative method

  12. Landslip monitoring

  13. Flowslides • Soil, clay, rock debris may behave like liquid; water content is > liquid limit • flowslide • Flowslides are extremely mobile • e.g. Yungay, Peru, 1970

  14. Mt. Huascaran, Peru, 1970 • earthquake triggered flowslide • hit towns of Yungay and Ranrahirca, 18 km away, at around 150 km/hr • Yungay completely buried, 66,000 dead

  15. Flowslide, Slumgullion, Colorado • National natural landslide laboratory • Major slip ~3500 years ago, present slip ~1000 years ago

  16. The Mam Tor head scar – looking west

  17. Mam Tor landslide • Occurred due to glacially oversteepened slopes • 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

  18. Cross-section through the Mam Tor landslip

  19. Geological map and movements at each station - 1996 to 2002

  20. Correlation of movements with rainfall

  21. An analogue for sedimentation in half-graben. Derbyshire County Council is the transportation agent!

  22. Mam Tor references • Skempton, A.W. et al., 1989, The Mam Tor 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.

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