Summary of key points

The design of slopes and embankments is not as simple as it would first appear from a superficial assessment of the partial factor approach. Unless the 'Single Source Principle' is invoked, Eurocode 7 requires different partial factors to be applied to unfavourable and favourable actions. However, this is not possible with typical limit equilibrium slope stability calculations, which cannot easily separate favourable and unfavourable actions.

For those Design Approaches that require permanent actions to be factored, one solution is to factor the soil's weight density. This amounts to treating both favourable and unfavourable actions as coming from a single source. Alternatively for these approaches an enhanced resistance factor is used.

It is evident from the analysis carried out in preparing the examples for this book that Design Approach 2 does not provide sufficient reliability in the design and is therefore unsuitable for slope stability analysis. As Chapter 6 revealed, most countries within Europe who have selected Design Approach 2 for general foundation design switch to Design Approach 3 for the design of slopes and embankments.

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