TECHNICAL
described above. One of the most cost-effective of these tech-niques
is the Rapid Impact Compaction (RIC) method.
The RIC system involves an excavator mounted hydraulic
hammer applying energy to the soil through a five-foot diam-eter
tamper foot, at the rate of 40 to 60 blows per minute.
Energy is then transferred to the ground safely and effi-ciently,
as the RIC’s foot remains in constant contact with
the ground. This system has been shown to be successful in
sandy soils, densifying loose-fill soils of up to six metres deep
or more, without the need for soil handling. The RIC system
can provide an improved geotechnical resistance of 150 kPa
or greater. In mixed fills, the RIC system has been used to
reduce the risk of differential settlement for relatively lightly
loaded floor slabs, often saving considerable time and cost
by avoiding structurally enhanced floor slabs. Savings going
from a structural slab back to a slab on grade could be $50 to
$100 per square metre.
The RIC solution is typically completed in two to three
passes of the site. Strike points are generally laid out within
the building footprint, as well as an additional apron
surrounding the building. The initial passes use a wider six-metre
by six-metre grid to ensure the RIC energy extends
deep to the lower soils. The surface craters created by the RIC
tamper foot are then bladed flat and a successive three-metre
by three-metre grid is completed. Additional strike points are
added if necessary after reviewing the on-board computer
diagnostics from the RIC rig.
The RIC on-board computer diagnostic system records
the number of blows and the travel of the tamper foot at each
location to understand the soil behavior with each succes-sive
blow. Along with visual observation by an experienced
technician, this diagnostic tool helps to clearly identify areas
on site which may require additional compactive effort to
achieve the target density. Densifying the soils in place also
results in an overall drop in the site elevation. Recording
the surface elevation prior to RIC and following completion
helps to qualitatively determine the reduction in voids within
the densified soil.
In some cases, a test section is completed on site in con-junction
with the geotechnical consultant to verify the
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