Ground investigation for footings

Annex B.3 of Eurocode 7 Part 2 provides outline guidance on the depth of investigation points for spread foundations, as illustrated in Figure 10.1. (See Chapter 4 for guidance on the spacing of investigation points.)

The recommended minimum depth of investigation, za, for spread foundations supporting high-rise structures and civil engineering projects is the greater of: za > 3bF and za > 6m where bF is the breadth of the foundation. For raft foundations: za > 1.5bB

where bB is the breadth of the raft.

The depth za may be reduced to 2m if the

Figure 10.1. Recommended depth of investigation for spread foundations z > 1.5b„

Figure 10.1. Recommended depth of investigation for spread foundations foundation is built on competent strata1 with 'distinct' (i.e. known) geology. With 'indistinct' geology, at least one borehole should go to at least 5m. If bedrock is encountered, it becomes the reference level for za.

Greater depths of investigation may be needed for very large or highly complex projects or where unfavourable geological conditions are encountered. [EN 1997-2 §B.3(2)NOTE and B.3(3)]

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