March/April 2023 - 91

Soil Improvement with
Mechanical Densification
The owner's geotechnical consultant
performed a site characterization in
July 2021. The report includes logs of
five borings drilled up to a maximum of
150 ft (46 m) below ground surface
throughout the proposed facility. Generally,
below 10-20 in (250-500 mm) of
asphalt and lime rock base were loose
to medium dense fine sands to 10-13 ft
(3-4 m) depth, underlain by very
loose/loose, fine sand to about 32 ft
(10 m) below ground level. Loose to
medium dense fine sands with a range
of shell and fractured limestone
content, along with pockets of moderately
hard to hard limestone were
encountered to about 70 ft (20 m) depth
and a stiff marine sand/silt layer to
78 ft (25 m) depth below which were
generally interbedded zones of medium
to dense sand and limestone.
Berkel evaluated support of the
structure with structural piles tied into a
mat foundation, however, an evaluation
of the soil profile indicated the unlikelihood
of a bearing capacity failure
leaving excessive total, and more
importantly, differential settlement as
the primary factor to consider for
support of the structure. This shifted the
focus of the foundation approach to
potential ground improvement systems.
The evaluation of the various design load
combinations on the structure resulted
in a design allowable bearing pressure of
10,500 psf (51,000 kg m2). This is
significantly larger than the allowable
bearing pressures that can be routinely
achieved through stone and aggregatebased
improvement systems. Therefore,
grouted rigid inclusions were the focus
of final design of the foundation system.
It is noted that the nature of the
cement dome, including the raised floor
and above-grade tunnel, meant that the
aggregate that was already planned for
dome construction could be used as an
effective load transfer platform between
the elements and the bottom of
the bin floor, eliminating the need for a
DEEP FOUNDATIONS * MAR/APR 2023 * 91
1: Drilling with clockwise
auger rotation and
vertical force
2: Pressure injection of
grout after reaching
the desired depth
3: Extraction of drilling
tool with clockwise
rotation
4: Insertion of
reinforcement:
completed APGD pile
Berkel's
Drilling
Tool
Drill
Stem
Pressure-grouted installation procedures for APGD piles and CGEs
reinforced concrete mat to support the
structure. However, the rigid inclusions
were then required at a spacing under
the proposed ring footing to provide a
localized increased bearing capacity for
these footings, considering the design
bearing pressure.
Dome load and rigid inclusion support
Both nondisplacement (augered)
and drilled displacement rigid inclusions
(CGEs) were considered;
however, the predominantly loose
sands underlying the site were
considered extremely well suited to
improvement by the mechanical

March/April 2023

Table of Contents for the Digital Edition of March/April 2023

TOC
March/April 2023 - Intro
March/April 2023 - 1
March/April 2023 - 2
March/April 2023 - TOC
March/April 2023 - 4
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