Slope Stability Analysis Flashcards
(48 cards)
What is the issue associated with using models in geotechnical engineering?
realistic simplification, rather than an exact imitation of reality, since geology and associated mechanical interactions can never be known in detail sufficient enough to allow unambiguous
representations
What abilities does the stability of a slope depend on?
Sustain load increases
Changes in environmental conditions, which may affect the geomaterials mechanically or chemically
What 2 steages are there to the analysis of slope stability?
Pre and post failure
Why is pre failure stability analysis undertaken?
applied to assess safety in a global sense to ensure
that the slope will perform as intended
Why is post failure stability analysis undertaken?
responsive to the totality of processes which led to failure
What are limit equillibrium methods?
Force and/or moment equilibrium conditions are examined on the basis of statics.
Analysis require information about material strength, but not stress- strain behaviour
What is the typical output for limit equillibrium method?
Factor of safety (FS)
What are the fundamental concepts of the limit equilibrium method for slope stability analysis?
Slip mechanism results in slope failure;
Resisting forces required to equilibrate disturbing mechanisms are from static solution
Shear resistance required for equilibrium is compared with available shear strength
Mechanism corresponding to the lowest FS is found by iteration
What will slip be like in isotropic materials?
surface tends to be circular
What type of material will isotropic/ circular slip be like?
HIghly jointed rock
Broken rock
Weathred rock, tailings or soil
What will slip be like with anisotropic material?
If ground has bedded or laminated structure with slipe tending to be elongated in direction parallel to structural feature
Mudstones, slate, schists
What is curvilinear slip?
Rotational slip
What will the effect on rotational slip be if a major structural feature is present?
If major dicontinuity, fault or clay seam in unstable area - slip surface will follow this as far as possible
What will slip be like in granular, low cohesion materials?
Granular nature with low cohesive strength curvature less marked (planar) and tension crack small/ non-existant
What will rotational slip be like in Inhomogenous materials?
presence of underlying bed of hard strong material can limit the failure extent
What are the assumptions of infinate slope analysis?
Slope face planar and of infinite length (relative to slide depth)
Failure surface // slope face
Influence of slope head and toe negligible
Vertical columns of equal dimensions through slope are identical
Groundwater table and any seepage // slope face
Soil contacts // slope face
What is the slide body represented as in infinite slope analysis?
Parrallelogram
What is the problem with infinte slope analysis?
Only consider a representative element in the slope
How does movement typically occur in translational landslides?
Planar failure surface
Often parallel to the slope
What might the failure plane be like for translational landslides?
weak bedding plane or joint surface, so the roughness of these surfaces partially controls friction
WHat is factor of safety like for dry non-cohesive slopes?
independent of slide thickness and slide
density or mass
What happens to the factor of safety if you increase the slope angle?
Decrease factor of safety
What does greater contact area do to cohesive forces?
Greater cohesive forces resisting sliding
What affects stability of saturated non-cohesive slopes?
Water increases Unit weight of soil – increases driving forces and if pore pressures are present reduced the
effective stress
Reduces the resisting force – Makes slope more unstable
