A design check with partial factors

Check a slope with partial factors on the soil strength, and read the over-design factor.

In a design to Eurocode 7 or to Swedish practice, the soil strength is divided by partial factors before the analysis. The slope is then adequate when the factor of safety on these design values is at least 1.0.

1. Switch the factors on

Start a new project with File › New. Open Model › Analysis › Options and tick Partial factors (design values). The Swedish set (EKS/IEG) is loaded; choose another under Preset… or edit the factors.

The Options window with partial factors switched on — Partial factors: γcu for undrained strength, γc' for cohesion, γφ' for tan φ' and γQ for loads.

2. Run

Click ▶ Run.

The result summary showing Min FOS (design values) of 0.757 — With c' and tan φ' divided by 1.3, the factor of safety on design values is 0.757.

The summary now reads Min FOS (design values). With the characteristic values the factor of safety was 0.984; on design values it is 0.757, well below 1.0. This slope does not satisfy the design check.

3. Interpreting the result

The value is an over-design factor: how much further the design values could be reduced before failure. A value of 1.0 or more means the design is satisfied. Do not compare it with a required global factor of safety; the partial factors already provide the margin.