Geotechnical Data and Pile Design - Offshore Structures: Design, Construction and Maintenance - page 244

As discussed before, in cohesion soil, for piles driven in undersized drilled
or jetted holes, the values of f and q shouldbedeterminedbysomemethod
that considers the effect of soil disturbance due to installation, but they should
not exceed values for driven piles. Except in unusual soil types, such as
described above, the f and q values given in Table 4.9 maybeusedfordrilled
and grouted piles, with consideration given to the strength of the soil-grout
interface.
The unit shaft friction values in cohesionless layers and the end-bearing
values for piles tipped in cohesionless layers with adjacent layers of lower
strength may also be taken from Table 4.9 , provided that the pile achieves pene-
tration of two to three diameters or more into the cohesionless layer, and the tip
is at least three diameters above the bottom of the layer, to preclude punch
through.
4.6.2 Foundation Size
In most cases, in the FEED engineering phase, the pile configuration will be
defined based on past experience. During selection of the size of the pile
foundation, the following should be considered: diameter, penetration, wall
thickness, type of tip, spacing, number of piles, geometry, location, seabed
restraint, material strength, installation method and other parameters as may
be appropriate.
A number of different analysis procedures may be utilized to determine the
requirements for a foundation. At a minimum, the procedure used should
properly simulate the nonlinear response behavior of the soil and ensure load-
deflection compatibility between the structure and the pile-soil system.
For deflections and rotations of individual piles, the total foundation system
should be checked at all critical locations, which may include pile tops, points
of contraflecture, mud line, etc. Deflections and rotations should not exceed ser-
viceability limits, which would render the structure inadequate for its intended
function.
Pile Penetration
The design pile penetration should be sufficient to develop adequate capacity to
resist the maximum computed axial bearing and pullout loads with an appropri-
ate factor of safety.
The ultimate pile capacities can be computed in accordance with previous
sections, or by other methods that are supported by reliable comprehensive
data. API RP2A (2007) defined the minimum factor of safety by dividing the
ultimate pile capacity into the actual load, as shown in Table 4.10 .
There are two safety factors in API RP2A that depend on considering the
design environmental conditions with the 100-year storm wave effect and the