Fellenius method (1927)

With this method (only valid for circular form slide surfaces) interslice forces are ignored and thereby the unknowns are reduced to:

Unknowns are (2n+1)

The available equations are:

1 equation of the global moments.

Actions on the i-the slice according to Fellenius

This equation is easy to solve, but it was found that provides conservative results (low safety factors) especially for deep surfaces or at the increase in the value of the pore pressure.