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Angle of shearing resistance, <|> (deg) Figure 9.6. Design chart for verifying limit state GEO using Design Approach 1, for an infinitely long slope with ru = 0.5

An example illustrates how to use this chart. Imagine a 2.5m thick slope which is required to stand at a gradient of 1:3. The slope comprises soil with characteristic weight density Yk = 20 kN/m3 and characteristic angle of shearing resistance 9 = 30°. From Figure 9.6, the characteristic stability number needed to verify a 1:3 slope is Nk = 0.115. Hence the characteristic effective cohesion c'k that the soil must possess is:

This is slightly less than was obtained in Section 9.4.1, because the equivalent global factor of safety for Design Approach 1 is 1.25 for = 30° (and was 1.3 in the previous example).

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