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The group efficiency depends on:
• The number, length, spacing, diameter, and

arrangement of the piles.
• The load transfer mode.
• The method of construction.
• The sequence of installation.
• The soil type.
• The elapsed time since piles were driven.
• The interaction between the pile cap and the

soil.
• The direction of the applied load.

1. Converse - Labarre Approach (1941) for Friction Piles:

This method relates the pile group geometry and group

efficiency.

The allowable vertical load capacity of pile group “Pag”:

Pag = η NQa  = 1- (n - 1) m + (m - 1) n
Where: 90 m n

N = Total number of piles

Qa = Allowable capacity of a single pile

η = Group efficiency;

q = tan-1 (D/S) in degrees;

D = Pile diameter (m);

S = Pile spacing (m);

n = Number of piles in a row;

m = Number of pile rows

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