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*Factor from Set A2 on geotechnical actions

*Factor from Set A2 on geotechnical actions

A second curve for Design Approach 1 is shown on Figure 9.5 with the label 'DA1 (using Yc,fav)'. This represents the alternative assumption which applies Yc,fav = 1.0 to favourable action effects. This curve lies above that for DA1 throughout and its equivalent global factor of safety is constant at F = 1.35.

The curve for Design Approach 2 (DA2) lies above that for DA1 when < 24°, but below it for larger values of Along this curve, the equivalent global factor of safety changes continuously from F = 1.485 at = 0° to F : 1.0 at 9k = 43° (not shown on Figure 9.5).

Figure 9.5. Stability number required to verify limit state GEO for a 1:3 infinite slope with ru = 0.5 according to Eurocode 7's Design Approaches

A second curve for Design Approach 2 is shown on Figure 9.5 with the label 'DA2 (using Yf)', which applies YG/fav = 1.0 to favourable action effects. This curve lies above that for DA2 throughout and its equivalent global factor of safety is constant at F = 1.485.

The curve for Design Approach 3 (DA3) lies below that for DA1 when < 11°, but is co-incident with it for larger values of Along this curve, the equivalent global factor of safety is constant at F = 1.25.

Hence the relative conservatism of the three Design Approaches is DA2 > DA1 > DA3 for <pk < 24° and DA1 > DA3 > DA2 for <pk > 24°.

Figure 9.5 shows quite clearly that Design Approach 2 does not provide a consistent level of reliability as the soil's angle of shearing resistance changes. Furthermore, DA2 produces a level of reliability that is much greater than that traditionally required of infinite slopes and therefore may be considered uneconomical.

Design Approaches 1 and 3 give identical results over the practical range of shearing resistance (9 > 18°).

9.4.3 Design charts for infinitely long slopes

Based on the preceding analysis, we have developed a series of design charts that allow infinitely long slopes to be designed according to Eurocode 7. The charts cover the verification of limit state GEO using Design Approach 1 and are presented in full in Appendix A. An example of one of these charts in shown in Figure 9.6.

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