Geotechnical Data and Pile Design - Offshore Structures: Design, Construction and Maintenance - page 263

Jardine et al. (2005) specify that plugged pile end-bearing capacity applies;
that is, the unit end-bearing Q p acts across the entire tip cross-section, only if
both the following conditions are met:

D i < 2 ð D r − 0 : 3 Þ

[Note: D i units are inches or m and D r units are not percentages, but
fractions.]
and

D i = D CPT < 0 : 083 q c,z < p a (4.33)

Should either of the above conditions not be met, then the pile will behave
unplugged and the following equation should be used for computing the end-
bearing capacity:

Q p = π t ð D − t Þ q c,z (4.34)

The full pile end bearing calculated by using Equation (4.32) for a plugged
pile should not be less than the end-bearing capacity of an unplugged pile cal-
culated from Equation (4.34) .

Offshore UWA-05
For friction, Lehane et al. (2005a) summarize the results of recent research work at
the University of Western Australia on development of axial pile design criteria of
open- and closed-ended piles driven into silica sands. The full design method
presented by Lehane et al. (2005a ,b) for unit friction on pipe piles includes a term
allowing for favorable effects of soil dilatancy (similar to ICP-05) and an empirical
term allowing for partial soil plugging during pile driving. Lehane et al. recommend
for offshore pile design to ignore the two favorable effects of dilatancy and partial
plugging. The original full design equations in Lehane et al. (2005a) will be used
for small-diameter piles, D

750 mm (30 inches), provided that larger factors of
safety are considered in the WSD design.
For end bearing, Lehane et al. (2005a,b) present design criteria for ultimate
unit end bearing of plugged open-ended pipe piles. Their full design method for
pipe piles includes an empirical term allowing for the favorable effect of partial
plugging during pile driving. For offshore pile design, Lehane et al. (2005a,b)
recommend this effect be ignored, resulting in the recommended design equa-
tion for plugged piles in the Offshore UWA-05 method:

<

Q p = q ca ð 0 : 15 + 0 : 45A r Þ (4.35)

Since the UWA-05 method considers nonplugging under static loading to be
exceptional for typical offshore piles, the method does not provide criteria for
unplugged piles.
The unit end-bearing q p calculated in Equation (4.35) is therefore acting
across the entire tip cross-section. The use of q c,av15D in Equation (4.35) is