Geotechnical Data and Pile Design - Offshore Structures: Design, Construction and Maintenance - page 262

TABLE 4.17 Unit Skin Friction Parameter Values for Driven Open-Ended

Steel Pipes (Simplified ICP-05 and Fugro-05 Methods)

Load
Direction Method a b c d e u v

4

p

Simplified
ICP-05

Compression 0.1 0.2 0.4 1 0 0.023 A r

4

p

Tension 0.1 0.2 0.4 1 0 0.016 A r

2

p

Fugro-05

Compression 0.05 0.45 0.90 0 1 0.043 A r

2

p

Tension 0.15 0.42 0.85 0 0 0.025 A r

Table 4.17 provides the recommended values for parameters a, b, c, d, e, u
and v for compression and tension, which are the unit skin friction parameter
values for driven open-ended steel piles for the Simplified ICP-05, Offshore
UWA-05 and Fugro-05 methods.
Additional recommendations for computing unit friction and end bearing for
all four CPT-based methods are presented in the following subsections.

Simplified ICP-05
A comprehensive overview of research work performed at Imperial College on
axial pile design criteria of open- and closed-ended piles in clay and sand is
presented by Jardine et al. (2005) . The design equations for unit friction in
sand in this publication include that unit friction is favorably influenced by
soil dilatancy. This influence reduces with increasing pile diameter.
The Simplified ICP-05 method as presented by API RP2A for unit skin
friction of open-ended pipe piles and the parameter values in Table 4.17 are
a conservative approximation of the full ICP-05 method, since dilatancy is
ignored and some parameter values were conservatively rounded up and
down.
Use of the original design equations in Jardine et al. (2005) may be consid-
ered, particularly for small-diameter piles (D 0.76 m), provided that larger

factors of safety are considered in the WSD design.
The ultimate unit end bearing for open-ended pipe piles, Q p , follows the
recommendations of Jardine et al. (2005) , which specify an ultimate unit end
bearing for plugged piles given by:

<

Q p = q ca f½ 0 : 5 − 0 : 25log10 ð D/D CPT Þ ≥ 0 : 15 q c,av,1 : 5D g (4.32)

where q ca is the average q cz value between 1.5 D o above oil tip to 1.5 D o below
pile tip level and D CPT is the CPT tools diameter (about 36 mm for a standard
1000 mm 2 base net cone).