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©As for Example 9.1, different partial factors (YG,fav and Yg) are applied to favourable and unfavourable effects of the soil's weight density.

© The slope does not satisfy Design Approach 2, but can be made to do so by lowering the water table to 2.5m or flattening the slope to 1 in 5.

& The result of verification to Design Approach 3 is identical to that obtained using Design Approach 1.

© The traditional global factor of safety for this situation is «1.2 which would be considered less than adequate for long-term conditions (for which F = 1.3 might be required).

© The calculations so far have considered the slope in its persistent state, but we should also check more extreme conditions, such as flooding to ground surface. Eurocode 7 allows 'extreme water pressures ... to be treated as accidental actions', for which Eurocode 7 specifies partial factors equal to 1.0 (i.e. lower than in the persistent case) - independent of Design Approach.

® The soil is just strong enough to withstand accidental flooding to ground surface.

9.8.3 Road cutting (using design charts)

Example 9.3 considers the design of a cutting for a new bypass, as shown in Figure 9.11. As there is no surcharge, we will use Taylor's charts to assess the safe slope angle for short and long term conditions.

Figure 9.11. Road cutting for bypass

Taylor's charts (see Figure 9.12) relate a stability number, the angle of friction of the soil and the angle of the slope. To use the chart in a conventional manner requires the same factor of safety to be applied both to c (i.e. effective cohesion c' or undrained strength cu) and to tan 9 to assess the factor of safety for the slope. However, a Eurocode 7 design requires partial factors to be applied to different parts of the equations (to actions, material properties, and resistances) and therefore the use of simple charts is made more complex. In the following example, we have highlighted how the partial

H=12m

H=12m factors may be applied for the three Design Approaches when using Taylor's charts.

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