CivilLab · Study Aid
Slope Stability · Method of Slices
What am I seeing?
- Moments are taken about the centre of the circle. Every slice base sits on that same circle, so the radius cancels and the factor of safety is just the sum of the base strengths over the sum of W sin α.
- α is steeply positive at the head, where the base drops away in the direction of sliding, and turns negative at the toe where the base rises. Those toe slices resist rather than drive, which is why cutting a slope at the toe is so dangerous.
- Fellenius ignores the forces between slices and resolves the weight straight onto the base, which loses some normal stress and always gives the lower answer. Bishop keeps vertical equilibrium and needs iteration because F sits on both sides.
- Pore pressure does not change the weight, only the effective normal stress on the base, so it eats into the friction term alone and leaves cohesion untouched.
- One circle tells you nothing on its own. The slope is only as safe as its worst circle, which is what the search button hunts for.