Pile Design and Construction Practice, Fifth edition

Pile groups under compressive loading 243

The comparative group settlements were

DEFPIG 42 mm

PGROUP 31 mm

Equivalent raft 30 mm

The principal problems concerned with pile groups are constructional effects such as
ground heave, the interference of closely spaced piles which have deviated from line during
driving, and the possibilities of damage to adjacent structures and services. It is, of course,
necessary to calculate the total and differential settlements of pile groups and overall piled
areas to ensure that these are within limits acceptable to the design of the superstructure.
The criteria of relative deflections, angular distortion, and horizontal strain which can be
tolerated by structures of various types have been reviewed by Burland and Wroth(5.2).
When checking group settlement calculations to verify compliance with serviceability
limit criteria, EC7 recommends a partial factor of 1.0 for actions and ground properties
unless otherwise specified.

5.2 Pile groups in fine-grained soils

5.2.1 Ultimate bearing capacity

It is sometimes the practice for regulatory authorities to require that each pile in a group
should be designed to carry a working load which has a conventional safety factor on

Total load on group 22.4 MN

GL

16.0 m

24.0 m

Rigid layer

Firm becoming

stiff normally

consolidated clay

48.0 m

30 MN/m^2

Ef 20 MN/m^2

Ed 60 MN/m^2

Equivalent raft 14×14 m

16 no. 600 mm OD piles at 1.8 m centres

1:4

Figure 5.4Pile group settlement by equivalent raft method.