Slope Stability Analysis

Question 1

What is the issue associated with using models in geotechnical engineering?

Answer 1

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

Question 2

What abilities does the stability of a slope depend on?

Answer 2

Sustain load increases
Changes in environmental conditions, which may affect the geomaterials mechanically or chemically

Question 3

What 2 steages are there to the analysis of slope stability?

Answer 3

Pre and post failure

Question 4

Why is pre failure stability analysis undertaken?

Answer 4

applied to assess safety in a global sense to ensure
that the slope will perform as intended

Question 5

Why is post failure stability analysis undertaken?

Answer 5

responsive to the totality of processes which led to failure

Question 6

What are limit equillibrium methods?

Answer 6

Force and/or moment equilibrium conditions are examined on the basis of statics.
Analysis require information about material strength, but not stress- strain behaviour

Question 7

What is the typical output for limit equillibrium method?

Answer 7

Factor of safety (FS)

Question 8

What are the fundamental concepts of the limit equilibrium method for slope stability analysis?

Answer 8

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

Question 9

What will slip be like in isotropic materials?

Answer 9

surface tends to be circular

Question 10

What type of material will isotropic/ circular slip be like?

Answer 10

HIghly jointed rock
Broken rock
Weathred rock, tailings or soil

Question 11

What will slip be like with anisotropic material?

Answer 11

If ground has bedded or laminated structure with slipe tending to be elongated in direction parallel to structural feature

Mudstones, slate, schists

Question 12

What is curvilinear slip?

Answer 12

Rotational slip

Question 13

What will the effect on rotational slip be if a major structural feature is present?

Answer 13

If major dicontinuity, fault or clay seam in unstable area - slip surface will follow this as far as possible

Question 14

What will slip be like in granular, low cohesion materials?

Answer 14

Granular nature with low cohesive strength curvature less marked (planar) and tension crack small/ non-existant

Question 15

What will rotational slip be like in Inhomogenous materials?

Answer 15

presence of underlying bed of hard strong material can limit the failure extent

Question 16

What are the assumptions of infinate slope analysis?

Answer 16

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

Question 17

What is the slide body represented as in infinite slope analysis?

Answer 17

Parrallelogram

Question 18

What is the problem with infinte slope analysis?

Answer 18

Only consider a representative element in the slope

Question 19

How does movement typically occur in translational landslides?

Answer 19

Planar failure surface
Often parallel to the slope

Question 20

What might the failure plane be like for translational landslides?

Answer 20

weak bedding plane or joint surface, so the roughness of these surfaces partially controls friction

Question 21

WHat is factor of safety like for dry non-cohesive slopes?

Answer 21

independent of slide thickness and slide
density or mass

Question 22

What happens to the factor of safety if you increase the slope angle?

Answer 22

Decrease factor of safety

Question 23

What does greater contact area do to cohesive forces?

Answer 23

Greater cohesive forces resisting sliding

Question 24

What affects stability of saturated non-cohesive slopes?

Answer 24

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

Question 25

What is Cu for short term analysis of undraine condtions?

Answer 25

Factor safety used for long term
Cu= strength of soil immediately after stress is applied and before enough groundwater flow has occurred to change void ratio e significantly