May/June 2021 - 77

consisting of R51N diameter rods were
installed with a yield strength of 141 kip
(630 kN) and with unit lengths of 59 ft
(18 m). This resulted in a total anchor
length of over 28 mi (45,000 m). These
elements were placed at an elevation of
about -27.9 ft (about El. -8.50 m) above
sea level. The insertion height of the
anchors was determined based on an
engineering study conducted on the
construction type of the quays (i.e., concrete
diaphragms cast in situ, prestressed
concrete sheet piles and steel
sheet piles), the lithology of the
subsurface in the Ravenna subsoil (i.e.,
alluvial soil - sandy and loamy), and the
loads acting on the quays, which ranged
from 2 to 6 tons per sq m (20 to 59 kPa).
The injection pressure was about
5,800 psi (400 bar), which was selected
to produce an anchor bulb with a
diameter of approximately 15.7 in
(40 cm). Execution of the core drilling on
such different structures was possible
by using an appropriate diamond crown
with a diameter of about 5 in (127 mm),
along with a rotational speed of 600
rpm. Injection activity was performed
using hollow bars, which had external
and internal diameters of 2 in (50.8 mm)
and 1.1 in (29 mm), respectively, with a
Underwater drilling rig carrying lattice with drilling cell across a quay
penetration rate of about 3 ft/min
(0.9 m/min), and with a rotational speed
of about 10 to12 rpm.
For the execution of the anchoring
bulb, a pozzolanic cement of class CEM
IV/A 32.5 R (UNI - EN 197-1 standard)
was used; this pozzolanic cement provides
resistance to sulphates, which
generate problems for concrete structures
in a marine environment.
During construction, it was also
possible to perform load tests, both on
the individual anchors to verify quality
and performance, and on some dredged
seabed materials in front of the quay.
The testing program included tension
verification of the anchors using
toroidal electric cells for the data
transmission, and the installation of
inclinometers and precision topographic
survey points to monitor the
structure during anchor testing. The
testing of the seabed area was carried
out by overloading the quay area with
loose material to better represent a
uniformly distributed load.
Design Scheme
The works executed using UWA were
performed at an elevation of about
-27.9 ft (El. -8.5 m), following a geological
survey that identified the geotechnical
properties of the various soil
layers, as well as the layer with the
best engineering characteristics for
anchoring.
The generalized stratigraphy of the
Site of anchoring work along port's south bank (red line); Ravenna's location (insert)
site is characterized by sandy banks
and silt-clayey layers of a sedimentary
depositional nature of the Po Valley
area. The peak unit resistance of the
sand bank, where the underwater
anchors were installed, ranged from
about 580 to 730 psi (4.0 and 5.0 MPa)
with a friction angle value (ø) on the
order of 30 to 32°, and an at-rest earth
pressure coefficient (K ), of 0.9, based on
dilatometric testing (DMT).
DEEP FOUNDATIONS * MAY/JUNE 2021 * 77
May/June 2021

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