Code of practice for foundations 2004 (Hong Kong) ada menyatakan dalam perkara 5.1.3 "minimum spacing" seperti berikut:
5.1.3 MINIMUM PILE SPACING
The spacing of piles shall be determined with due regard to the nature of the ground, the method of construction, the group effects and shall be sufficient to prevent damage to the piles or any adjacent construction.
For driven piles and other piles, which derive their capacities mainly from frictional resistance, the minimum pile spacing shall be not less than the length of the perimeter of the pile or 1m, whichever is the greater, and the piles shall be placed at not less than half the length of the perimeter of the pile or 500 mm, whichever is the greater, from the site boundary.
For mini-piles, which derive their capacities mainly from bond strength between grout and rock, the minimum pile spacing should be 750mm or 2 times the outer diameter, whichever is the greater.
For bored piles and the like which derive their capacities mainly from end bearing, the minimum clear spacing between the surfaces of adjacent piles should be based on practical considerations of positional and verticality tolerances of piles. It is recommended to provide a nominal minimum clear horizontal spacing of 500 mm
between shaft surfaces or edge of bell-outs, as appropriate.
5.1.2 GROUP EFFECT
A pile group exists when piles are closely placed such that the load carrying capacity
and settlement behaviour of a pile may be affected by other piles.
In such case, a group reduction factor determined by recognized foundation engineering principles shall be applied to the total allowable load carrying capacities of any group of piles. A group reduction factor of 0.85 may be considered as generally acceptable for a group of 5 or more vertically loaded piles. Other values of group reduction factor may be used having considered the particular ground condition of the site and justified by recognized engineering principles.
Generally, group reduction factors need not be applied where :
(a) the centre-to-centre spacings are of more than 3 times the perimeter of the piles
or the circumscribed rectangles in the case of H-piles; or
(b) the load capacity of the piles is derived from end-bearing; or
(c) the piles are rock-socketed piles; or
(d) the piles are driven to refusal with the toes resting closely onto bedrock (see