bedrock to zones with bedrock measuring
as deep as 110 feet below the seafloor and
closely followed the steep profiles of adjacent
Mount Roberts and Mount Juneau.
Given the large foundation loads associated
with the cruise ship berths, PND needed to
design the foundation elements so that they
could transfer these forces to the seafloor
and underlying bedrock.
PND developed a geotechnical investigation
program to characterize the general
site ground conditions along with specific
ground characteristics at the locations of
deep foundation elements for the dolphin
and mooring structures. PND characterized
the ground conditions by taking in-situ
standard penetration test (SPT) readings
and vane shear tests. Additionally, test pile
probes were driven at each planned dolphin
location to confirm bedrock elevation.
The water depth, bedrock variability
and large forces from new generation ships
meant that large, driven steel pipe piles were
the most economically viable way to support
and anchor the marine structures because
they could be supplied in the necessary
length for the project and could be readily
anchored to the bedrock. With the presence
of shallow, steep and sloping bedrock at the
site, and the need to resist large shear and
tension forces with the piles, PND incorporated
several different pile tip anchoring
elements into the design. For piles with high
shear or tension forces driven into little or
no overburden, rock anchors were incorporated
to resist these forces by transferring
the force directly from a tensioned anchor
at the top of the pile directly into the bedrock.
For piles in shallow bedrock subject to
large bending forces, rock socketed pile tips
with rock anchors were incorporated into
the design so that the full flexural capacity
of the pile could be transferred to the
bedrock. Finally, for piles required to resist
large tension loads in locations with moderate
overburden depths, PND used SPIN
FIN® pile tips. These pile tips consist of a
series of straight steel plates welded to the
tip of the steel pipe piles in a helical pattern.
When driven and attached to a structure
to prevent rotation, the SPIN FIN® tips
enhance the resistance to compression forces
by providing additional skin friction area
and bearing area for the pile to resist forces.
Construction innovation
Given the variability of soft soils underlying
the project site, additional verification
of driven pile tension capacities was
necessary. Compression capacities of the
piles were established by firmly seating the
piles in the underlying bedrock with an
impact hammer.
PND’s engineers performed field pile
driving inspection throughout construction
of the project. As part of the pile driving
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