Note that the results obtained from a Design Approach 2 analysis depend critically on how the partial factors are applied. Neither of the two methods described in © and © above is commensurate with traditional practice, which is to search for a required (material) factor of safety of 1.3. Owing to these uncertainties, Design Approach 2 is not recommended for slope stability assessments.

© The approach for Design Approach 3 (DA3) is identical to that for DA1-1, except that the imposed surcharge is treated as a geotechnical - rather than structural - action (and hence is less onerous).

© The required factor of safety for a traditional analysis is not prescribed, but a value of 1.3 is often considered acceptable for long-term analysis.

© Both DA1-2 and DA3 imply similar degrees of utilization to the traditional analysis. This gives confidence that the manner of applying the partial factors in DA1-2 and DA3 is sensible and likely to yield reliable designs.

Where the perceived level of risk cannot be accounted for by using the partial factors prescribed in EN 1997-1, greater conservatism would be required in the assessment of the characteristic values for the material properties.

9.8.5 Road embankment over an alluvial flood plain

Example 9.5 considers a road embankment that is going to be constructed over an alluvial flood plain, as shown in Figure 9.14, where ground conditions comprise 2m of soft, very low strength CLAY, overlying 3m of loose SAND, overlying firm, medium strength CLAY.

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