Design situations and limit states

Possible limit states for pile foundations are illustrated in Figure 13.2, from left to right: (top) ground and (middle) structural failure, in compression, tension, and under transverse loading; and (bottom) failure by buckling, shear, and bending.

Pile foundations are used to support buildings and bridges, typically when the upper strata have insufficient bearing capacity to carry the loads or, more commonly, the settlement of a shallow footing exceeds the acceptable limit for the structure.

Eurocode 7 Part 1 contains a long list of design considerations for pile foundations, some of which are mandatory ('shall be taken into account') and some of which are optional ('should receive attention'). For example, the choice of pile type must account for stresses generated during installation and the effect of installation on adjacent structures; while installation-induced vibrations and soil disturbance from boring should be considered.

When either designing a pile group or selecting a pile type these lists provide a useful check to ensure that key factors have not been forgotten. The statements and associated lists do not cover everything that needs to be considered but act as useful aides-memoirs. Whether items are 'shall' or 'should' reflects their relative importance - although 'should' statements are not mandatory, they do reflect good practice, thus the sensible designer will not ignore them.

fi.e. weaker strata are unlikely to occur at depth, structural weaknesses such as faults are absent, and solution features and other voids are not expected.

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