CIVE1105 Rock Slope Stability

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Author:
higgsboson
ID:
223237
Filename:
CIVE1105 Rock Slope Stability
Updated:
2013-06-25 06:53:40
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Rock Slope Stability
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Description Week 9&10 lecture notes summary. Exam
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  1. Rock slope failure mechanism:
    • Continuum
    • Discontinuum
  2. Basic rock failure mechanism
    • a.) circular slip
    • b.) plane sliding
    • c.) wedge sliding
    • d.) toppling
    • (page 21, week 9 lecture)
  3. Stabilisation measures for failure mechanisms
    • Key parameters: slope geometry, joint strength, joint water pressure (water conditions).
    • Also failure mode, slope geology & structures, material properties,
    • (p 32 week 9)
  4. Rock slope stabilisation methods
    • - sprayed concrete
    • - weep holes
    • - dowels
    • - dentition
    • - rock bolts, rock anchors
    • - drain holes
    • - mesh
  5. Design considerations
    • - ensure slope stability
    • - reduce excavation cost
    • - optimize design
  6. What are the parameters/factors that control the stability of the rock slope?
    • Slope geometry
    • Joint strength
    • Water pressure
  7. Internal and External loads
    • Internal loads: Gravity and hydraulic pressure
    • External loads: can be restraining/resisting/stabilizing forces, (e.g. cable, bolt, anchors) or disturbing/sliding/destabilizing, (e.g. additional load from traffic ).
  8. Forces acting on unstable block
    • Weight of block - need to know the cross-sectional area, the density of the rock
    • Hydraulic forces - depend on the distribution of groundwater in the slope
    • Shear resistance - depends on the shear strength
  9. Factor of Safety against sliding
    • =
    • Forces resisting sliding / Forces causing sliding
  10. Tension crack
    It is not uncommon to find a Tension crack developing behind the crest of a slope as it begins to fail. It isn't always there and it isn't always visible even if it is there. Need to consider the possibility because water in this crack will push the blocks out of the slope and allow water to get under the base of a sliding block.
  11. Measurement of shear strength of joints
    • τ = σ tan(φ) = c + σ'tan(φ)
    • σ is the stress applied normal to the shear plane
    • φ is the angle of shearing resistance (in soil mechanics, φ is called the internal friction angle)
  12. Simple model

    • interface: N = W cosΨ + T sinβ
    • S = W sinΨ - T cosβ
    • FoS =
    • (W cosΨ + T sinβ) tan φ/W sinΨ - T cosβ

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