May/June 2021 - 78

mitigate possible problems that could
arise during the life of the structure (e.g.,
issues with the anchor losing resistance,
corrosion effects, etc.) and sudden
exceedance of prescribed threshold
values by unanticipated external
actions. Regardless, 11 years after the
first anchors were installed, and with
added checks by divers, the stress states
have remained within the working
ranges of the anchoring, without
significant variations. Furthermore,
visual checks have indicated that
correct conservation of the load distribution
structures (e.g., plates and
bolting) have been maintained.
Conclusions
Side view of underwater tie rod, including load test parameters
Geotechnical design parameters
were inferred based on the stratigraphy
at the project site and the data obtained
from the tests. The assumed parameters
were used to characterize the soils for
the design of the anchoring system, to
analyze structure-soil interaction to
determine the anticipated shear
strengths and deformation, and to
perform the required tension testing on
the installed anchor. The maximum
grout-to-ground unit bond resistance
(τ ) was determined based on the
lim
available side resistance along the
anchor's bond length, which was a
function of the lithostatic confinement
pressure (σ ) acting at the mid-depth
'v
along the anchor's bond zone. For the
proposed anchor design, this criterion
resulted in a τ =14.3 psi (99 kPa), for a
lim
σ = 23.1 psi (159 kPa).
'v
78 * DEEP FOUNDATIONS * MAY/JUNE 2021
The as-constructed size of the anchor
was determined based on the injected
grout volumes, injection pressures and
penetration/advancement rate of the
minijet system. The equivalent diameter
was conservatively estimated to
be approximately 15.7 in (400 mm).
The stress state of the quay face was
found to be substantially unchanged by
the changes made to the structure. This
was determined by investigating the
moments of the structure, before and
after the installation of anchors.
Monitoring of the anchors continues,
and involves toroidal cells that
were installed for verification tension
testing, which provides the Port
Authority a constant control of the
anchors. By being able to verify the
tension load in the anchors, the Port
Authority is able to anticipate and
The underwater anchoring technology
described has the advantage of being
concentrated in one vehicle (an excavator),
and involves only two equipment
operators. Software coupled with
sensors and cameras integrated on the
excavator control the robotic execution
of the step-by-step drilling and anchoring
and allow complete control from the
cab of all operations performed in the
water. The approach minimizes the use
of divers to increase safety. The UWA
technology is therefore a flexible, agile
and easy way to save money and time
when pursuing dock renovation work.
The quays at the Port of Ravenna
were successfully adapted to a new
seabed depth in line with Italian
legislation. The modifications were
performed without interrupting the
terminal's operations and activity,
whereas other design solutions would
have had a major economic impact by
interrupting commercial traffic in the
quays for a considerable time. Avoiding
interruptions was possible because the
excavator and its mechanical arm could
be moved within 30 minutes if a ship
needed to moor at a quay where the
anchors were being installed. The UWA
machine would then resume anchoring
from the point where it was interrupted.
The underwater intervention,
therefore, made it possible to optimize
May/June 2021

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