Pile Design and Construction Practice, Fifth edition

Effective lengths for reinforced concrete piles when regarded as columns are defined by
EC2 (Clause 5.8.3.2):

Restrained at both ends in position and direction: 0.5 L

Restrained at both ends in position and one end in direction: 0.7 L

Restrained at both ends in position but not in direction: 1.0 L

Restrained at one end in position and direction and at the other end in

direction but not in position: 1.0 L

Restrained at one end in position and direction and free at the other end: 2.0 L

EC3 (BSEN 1993-1-1: 2005) is currently silent on effective lengths for steel piles
when regarded as columns, requiring the application of the guidance given in BS 5950
part 1, which is slightly different from the above factors.
A pile embedded in the soil can be regarded as properly restrained in position and
direction at the point of virtual fixity in the soil. The restraint at the upper end depends
on the design of the pile cap and the extent to which the pile cap is restrained against
movement by its connection with adjacent pile caps or structures. Some typical cases of
the restraint of piles are shown in Figure 7.4a to e. The condition shown in Figure 7.4e

384 Structural design of piles and pile groups

Raking piles in

four

directions

Tie beams holding

pile cap in position

Tie beams

holding pile cap

in position

Hard rock

Cable

anchors

Soft

clay

(a) (b)

(c) (d) (e)

Figure 7.4Conditions of restraint for vertical piles (a) Restrained at top and bottom in position and
direction (b) Restrained at bottom in position and direction; restrained at top in position
but not in direction (c) Restrained at top and bottom in position but not in direction
(d) Restrained at bottom in position and direction; restrained at top in direction but not
in position (e) Restrained at bottom in position and direction; unrestrained at top in
position or direction.