TECHNICAL
Got Them Sandy Soil Blues?
The Densipact® system may be just what your project needs
By Mark Tigchelaar, P.Eng.
Sandy soil can be found throughout all regions of
Canada and oftentimes in areas of planned development
for large, load-bearing structures. This poses distinct
foundation challenges to engineers, contractors and
developers. Construction of pretty much any substantial
structure on sandy soil has the potential for disaster based
on the naturally shifting characteristics of sand.
Loose sand can be subject to large settlements and these
settlements tend to occur quickly due to the free-draining
granular nature of sand. To further complicate matters,
clean sands (sands with fewer fine particles mixed in)
underwater can be prone to liquefaction (water build-up)
when subjected to excitation such as vibrations or seismic
forces. Seismic forces cause a liquefaction increase in pore
pressure to a point where the sand becomes suspended
and the natural angularity of the sand no longer affords
high shear strength. The temporarily suspended sand-inwater
mixture behaves like a liquid and any objects sink to
a point where the weight of the object is equal to the weight
of the sand-water liquid. Once the excitation stops and pore
pressure dissipates, the sand becomes frictional again and
the settlement stops, but by then significant damage to the
structure above has already occurred.
Loose sandy soil, regardless of its specific characteristics,
requires significant densification to provide sufficient settlement
control and sound bearing pressure for new structures being built.
Strange looking, but effective
An innovative system to effectively combat the challenge
of sandy soils is the Geopier Densipact® system, designed
through research by the Geopier Foundation Company
based out of North Carolina that has been at the forefront
of the development of groundbreaking ground improvement
systems for many decades. Their Densipact® system was
designed specifically for sandy soils for both settlement control
and liquefaction mitigation and to densify loose sandy soils
to depths of 25 to 30 feet.
This high-performing system provides unsurpassed
strength and stiffness, eliminates casing and allows for
construction in soils that are prone to cave-ins, high water
levels and liquefaction. Additionally, the Densipact® system
provides very high bearing pressures to ensure consistently
high levels of performance and reliability. The Densipact®
system creates Rammed Compaction® points by repeatedly
driving a multi-tined tool into the ground using high
frequency, vertical impact energy and downward crowd force
to improve granular soils. The result is a significant increase
PHOTO COURTESY OF GEOPIER FOUNDATION COMPANY
PILING CANADA 59