CRITICAL FAILURE SURFACE:
In homogeneous soils relatively
unaffected by faults or bedding, deep seated shear failure surfaces tend
to form in a circular, rotational manner.
We aim to find the most dangerous,
ie.the most critical surface, and using the assumption above, we can find
this surface using "trial circles".
The method is as follows:-
- Consider a series of slip circles
of different radii but the same centre of rotation. Plot the Factor of
Safety (FoS) for each of these circles against radius, and find the minimum
- This should be repeated for several
circles, each investigated from an array of centres. The simplest way to
do this is to form a rectangular grid from the centres:-
- Each centre will have a minimum
FoS, and the overall lowest FoS from all the centres shows tha FoS for
the whole slope. This assumes that enough circles, with a large spread
of radii , and a large grid of centres have been investigated.
- We then have an overall failure,
surface, with smaller individual ones which should not be ignored.