R

Material strength

Figure 6.16. Hierarchy of parameters for Design Approach 3

An important feature of Design Approach 3 is the distinction between structural and geotechnical actions — larger factors are applied to the former than to the latter, suggesting greater uncertainty in their values. A geotechnical action is defined as an:

action transmitted to the structure by the ground, fill[, standing waterf] or groundwater. [en 1990 §1.5.3.7] and [en 1997-1 §1.5.2.1]

Eurocode 7 does not explicitly define what a structural action is, but by implication it is an action that is not geotechnical.

Figure 6.17 shows some design situations where the distinction between structural and geotechnical actions is not straightforward. Strict interpretation of the definition above results in traffic action applied to the gravity wall being classified as a geotechnical action!

The table below summarizes several alternative definitions for 'geotechnical action' and applies them to the design situations shown in Figure 6.17. None is without problems. Fortunately, as Section 6.3.4 below shows, this issue has become largely academic because Design Approach 3 is almost exclusively being used for the design of slopes, where all actions (including traffic) should be treated as geotechnical.

Figure 6.17. Situations where definition of geotechnical action is unclear

fText in brackets omitted in EN 1990.

Definition of geotechnical action

Concrete in wall/ footing

Backfill on ...

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