7.2.1 Suction piles should be designed in accordance with industry recognised
practice such as ISO 19901-7.
7.2.2 Suction piles are characterised by having a large diameter and a length
to diameter ratio generally less than eight, and are essentially caisson-type
foundations if the length to diameter ratio is less than three.
7.2.3 Table 14.7.1 defines the design cases and factors of safety to be used
for suction anchor piles for a catenary mooring system. Table 14.7.2 defines the
design cases and factors of safety to be used for suction anchor piles for a
taut-leg mooring system. The axial and lateral factors of safety for suction piles
should be accounted for within in the analyses as described within ISO 19901-7
taking account of whether axial loading, lateral loading or combined axial-lateral
loading controls the anchor design.
Table 14.7.1 Minimum factors of safety for
suction anchor piles for a catenary mooring system
| Design case
|
Anchor load case
|
Factor of safety
|
| Axial loading
|
Lateral loading
|
| Intact
|
Static load, see Note 1
|
2,0
|
2,0
|
| Intact
|
Dynamic load, see Note 2
|
1,5
|
1,5
|
| Damaged
|
Dynamic load
|
1,5
|
1,5
|
|
NOTES
1.Static load refers to steady plus low
frequency components of loading.
2.Dynamic load refers to static plus wave
frequency components of loading.
|
Table 14.7.2 Minimum factors of safety for
anchor piles for a taut-leg mooring system
| Design case
|
Anchor load case
|
Factor of safety
|
| Axial loading
|
Lateral loading
|
| Intact
|
Static load, see Note 1
|
2,7
|
2,0
|
| Intact
|
Dynamic load, see Note 2
|
2,0
|
1,5
|
| Damaged
|
Dynamic load
|
2,0
|
1,5
|
|
NOTES
1. Static load refers to steady
plus low frequency, components of loading.
2. Dynamic load refers to static
plus wave frequency components of loading.
|
7.2.4 Suction anchor pile analysis is generally performed using either a
continuum finite element model or a limit plasticity model of the pile and soil in
order to assess appropriate failure modes. Pile response and the determination of
soil reaction stresses for structural analysis of the suction anchor pile are to be
analysed using non-linear soil/structure interaction finite element analyses.
7.2.5 The influence of pile shoes, internal stiffeners, padeye and any other
protrusions should be accounted for within the pile capacity and installation
assessments.
7.2.6 For suction anchor piles subjected to permanent tension loads,
consideration is to be given to long term changes to soil stresses around the
suction anchor pile and upward creep.
7.2.7 For tension loads, no end bearing (or suction) component at the pile tip
is to be considered unless this can be justified based on pile configuration, rate
of loading and soil permeability.
7.2.8 Consideration is to be given to the possible formation of a post-hole at
the pile head and its effect on capacity