July/August 2024 - 101

properties, underlain by highly
compressible cohesive organogenic
soils (silts and clays), fine to medium
grained silty sands with moderate loadbearing
capacity and very soft to soft
lacustrine clay deposits (alluvium) with
unfavorable geotechnical properties.
On account of the unfavorable
subsoil conditions, a shallow foundation
was not feasible and a deep
foundation solution for the substructure
(abutments and piers) was unavoidable.
Nevertheless, due to the
presence of high compressible lacustrine
clays, encountered up to the
investigation depth of 50 m (164 ft)
below natural ground level, a classical
solution based on end-bearing piles
(i.e., cast-in-place bored piles or drilled
shafts) with reasonable lengths was
unsuitable for the foundation of the
substructure.
Proposed Solution
As an alternative to end-bearing piles,
downwards fanned out pile grillages (a
combination of vertical and racked
floating piles) were proposed to support
the substructure with the goal to obtain
the largest possible area to achieve an
optimum load distribution to maintain
the deformations (settlements) within
acceptable ranges.
Piling System
An extensive analysis of different
piling systems was conducted for the
project, and the most suitable and costeffective
solution was provided by
ductile iron piles due to the flexibility,
large adaptability and velocity of the
installation.
These are low vibration, driven, fulldisplacement
piles, installed using a
medium-sized excavator and a hydraulic
breaker hammer with a
modified shank that seats into the pile
socket (bell) for driving, using the
hammer 's percussive energy. The
hydraulic hammers typically range
from 1,200-2,500 kg (2,645-5,500 lb)
and operate at frequencies ranging
Fussach side of the bridge longitudinal view (top) and plan view (bottom)
from 250-500 blows per minute. The
hammer size (energy) is matched with
the size of the pile and the subgrade
driving conditions to develop the most
efficient installation while not overstressing
the pile material.
Ductile iron piles are used to transfer
loads from the superstructure into
the lower soil layers and to limit
deformations according to the principles
of executing geotechnical work,
and have the flexibility to be installed
to transfer the loads developing skin
friction and end-bearing capacity. For
this project, frictional (grouted) ductile
iron piles were adopted.
Similar to micropiles in soil, frictional
ductile iron piles generate
compression or tension capacity by
creating a grouted bond zone within
competent soil layers. Piles designed for
frictional resistance are installed by
first fitting an oversized conical grouted
pile shoe on the ground at the pile
locations. Conical grout shoes range in
diameter from 150 mm (6 in) up to 370 mm
(14.5 in), depending on pile size and
design requirements. The initial pile
section is then positioned onto the shoe
and driven into the ground using the
vertical percussion energy of the
hammer, which now requires a grouting
DEEP FOUNDATIONS * JULY/AUG 2024 * 101
Hard side of the bridge longitudinal view (top) and plan view (bottom)
July/August 2024

Table of Contents for the Digital Edition of July/August 2024
