IN LIMIT EQUILIBRIUM:
We need to make certain assumptions
in analysing slopes using limit equilibrium:-
- Assume a Failure Mechanism: We
assume the shape and location of a failure surface rather then determining
it by analysis.
- Assume Plane-Strain (2-D):We ignore
3-D effects (although of course in reality slopes are in three dimensions).
We are being conservative by neglecting these effects, ie. we would achieve
higher FoS's by taking them into account.
- Assume Rigid Block Movement: We
assume the soil mass to moove as a rigid block, with the movement only
taking place on the failure surface itself.
- Assume Uniform Localisation of
Shear Stresses: As previously discussed in "Progressive Failure",
the shear stresses are not usually uniformly mobilised over the whole length
of the failure surface. However, for the purpose of our analysis, we assume