An embankment dam

A zoned dam analysed from right to left, and the Morgenstern–Price λ plot.

This tutorial uses the Talbingo dam, a rockfill dam with a clay core and a published benchmark for slope stability programs. Open Help › Benchmarks and click Talbingo Dam.

A dam cross-section with rockfill shells, transition and filter zones and a clay core — Rockfill shells (yellow), transition and filter zones, and the clay core.

1. The zones

Open Model › Materials › Define. The rockfill, transition and filter are frictional (φ = 45°, γ = 20.4 kN/m³); the core is a clay with c = 85 kPa and φ = 23° (γ = 18.1 kN/m³).

The Define Materials window with four dam materials — Four materials, one per zone.

2. Direction

This section fails towards the left. In Model › Analysis › Options, Analysis Direction is set to Right to left. For a slope where either face could fail, tick Analyse both sliding directions instead.

3. Run

Click ▶ Run.

The critical slip surface through the upstream shell of the dam — The critical surface lies in the rockfill of the face.

The factor of safety is 1.95, equal to the published value.

4. Check the equilibrium

Morgenstern–Price finds the factor of safety where moment and force equilibrium give the same value. Open Results › Plots › Results Plot and choose Lambda vs Fm/Ff:

Factor of safety from moment and force equilibrium against lambda — Fm (moment) and Ff (force) against λ. The solution is where they agree within the tolerance: here λ = 0.4 and F = 1.951.

In a frictional shell the two curves lie close together: the result hardly depends on the interslice forces. Where they diverge strongly, the choice of interslice function matters more.

Reinforcing a slope with soil nails.

An embankment dam

1. The zones

2. Direction

3. Run

4. Check the equilibrium

Next