have increasingly more and more problems. Furthermore,
the rules for handling excess soils have tightened exponentially
over the last 10 to 20 years, so much so that excess soils
are almost considered a waste now unless you go through
rigorous testing for various ‘contaminants’ to make sure it’s
usable and safe.”
Rammed aggregate piers
The company recently installed over 6,000 displacement
rammed aggregate piers (RAPs) on reclaimed land near the
shore of Lake Ontario for a Toronto Transit Commission
streetcar facility. The site had infill containing organics over
organic silt and clay and zones of trapped peat over a glacial
till and bedrock 35 to 40 feet deep.
“This is a fairly typical profile for the area – a hundred
years ago, it was essentially all lake,” said Tigchelaar.
With the RAP impact system, a hollow mandrel and a
hopper with a stone valve are pushed or vibrated into the
ground to the desired pier depth, and then raised a pre-set
distance while discharging stone – the valve allows the stone
to flow through the mandrel when it is raised and closes to
form a front to compact the stone when it is pushed down.
The last two steps are repeated until the pier is complete.
“In the Geopier process, when you push out a cavity in
the ground and ram stone laterally, you laterally stress and
increase the capacity of the soil around the cavity. The undulated
shape of the well-compacted rammed aggregate pier
supports the load by friction by coupling the pier with the
locked-in lateral stress of the surrounding soil,” he said, and
can also completely eliminate or minimize spoils. Groups
of RAPs with diameters ranging from 18 to 36 inches can be
driven to depths of 10 to 60 feet or more, depending on a project’s
requirements and soil conditions.
“In some cases, as with the TTC project, we added grout
to the piers to help increase their internal shear strength
through some very poor soil zones,” he said; grouted impact
elements can be three to 10 times stiffer than RAP systems
alone. The massive project took three crews only about five
months to complete, he said, “and the structure is performing
as designed, verified through many load tests on site,
including full-scale footing tests, and settlement monitoring
following building construction.”
Finding the right technique
In addition to ground improvement techniques, GeoSolv’s
various piling systems can offer distinct advantages for certain
types of projects. One system relies on sections of rigid
ductile iron pipe pile (DIPs) that are similar in strength but are
much more corrosion-resistant than steel, says Tigchelaar.
“You can design DIPs like friction micropiles or like endbearing
pipe piles,” he said, to accommodate a range of
ground conditions, such as on contaminated sites, where
soils consist of loose sands or soft silts, or where groundwater
is high.
AMONG GEOSOLV’S
INNOVATIVE FOUNDATION
SOLUTIONS:
To build Geopier GeoConcrete Columns (GCCs), ready-mix
concrete is pumped into the mandrel of a pressure vessel with
stone valve at its base, driven to the underlying competent
soils using full displacement, crowd force and vertical
ramming energy, forming a bottom bulb and a smallerdiameter
column of concrete extruded to the surface. Groups
of elements are separated from the high-capacity spread
footing (up to 450 kPa SLS) using a load transfer cushion.
Ductile Iron Piles (DIPs) can be easily installed in tightaccess
sites and from varying grades using relatively
small, low-vibration equipment. Manufactured from
recycled metals, the high-capacity modular pipe
sections can be quickly driven to end-bearing refusal or
grouted during driving to develop friction capacity.
When Geopier Rammed Aggregate Piers (RAPs) are
installed below foundation elements they create
stiff columns of compacted aggregate, which densify
the surrounding soils and result in a soil mass with
higher strength and less compressibility and allow
for the use of high-capacity spread footings.
“One of the biggest advantages
over deep foundations is the use
of conventional construction using
standard spread footings and
unreinforced slabs.”
– Mark Tigchelaar, GeoSolv
COMPANY PROFILE
CONTINUED ON PAGE 58
56 Q4 2016 www.pilingcanada.ca
/www.pilingcanada.ca
/www.pilingcanada.ca
/www.pilingcanada.ca
