Underground Infrastructure - June 2023 - 33

Asset Management
Continued progress
Every iteration of GPR has been lighter, faster and more user-friendly
than its predecessor.
GPRS Contract Locating Manager John Kessinger was one
of the company's earliest employees. He started in 2002 as a
project manager, and he can still vividly remember being in the
field conducting utility locates and concrete scans.
What he recalls most is that the GPR scanners of his day were
unwieldy and heavy. While similar in size to today's carts, the
original units were constructed with traditional metals, rather
than lightweight carbon fiber. Their acid batteries were much
heavier than the lithium-ion cells that power today's scanners,
and their displays were thicker and less user-friendly than modern
touchscreens.
The improvements in GPR technology are even more obvious
when you compare the concrete scanning units used by
Kessinger's era to today's devices.
In 2005, Kessinger was called to Jackson, Mississippi, to
scan precast concrete walls to verify the location of reinforcing
steel as part of construction of a new Bass Pro Shops store.
Today, this would be a straightforward job accomplished in a
couple of hours, thanks to the mobility of the handheld Proceq
GP8800 GPR Scanner, GPRS' current scanner of choice for
investigating concrete.
It was a little more complicated for Kessinger who, more
than 20 years ago, used the top-of-the-line GSSI SIR-20 system,
which had to be physically connected to a Panasonic
Toughbook computer. Including its cart, the system weighed
close to 100 pounds.
" I remember just having cords, having all this equipment,
the setup, " Kessinger said. " It really wasn't as conducive as
today where we have small antennas that really don't have the
cables and cords.
" The job was done, it was a successful job, but it was just hard
on the body a little bit to do the scanning. "
Limitations
Every tool has its limitations, whether you're talking about
something as simple as a hammer or as sophisticated as ground
penetrating radar.
Soil type plays a huge factor when using GPR for utility locating.
Highly conductive soils, such as clay, are harder for GPR to
penetrate. However, modern GPR units, like the ImpulseRadar,
are less inhibited by this problem, due to their dual-channel operation.
This allows for one-pass locates at both high and low
frequencies to scan both shallow and deep into the soil.
Moisture also plays havoc on GPR's effectiveness. Freshly
cured concrete still has a lot of moisture inside and is, therefore,
more difficult for GPR to penetrate than older, dryer concrete.
GPR can still be useful in situations where it is hindered by
its limitations.
Back at the Ford Research & Engineering Center, Merrell
has been called out to help the contractor locate the main utility
connection points on the property. The pipes in question are
A close-up shot of a Proceq GP8800 GPR Scanner, GPRS' current scanner of
choice for investigating concrete slabs and structures. (Photo courtesy of GPRS)
believed to be transite, or asbestos-cement (AC) pipes, that are
buried 9 feet below the ground. It is next to impossible to detect
them with GPR or EM locating, so instead, an excavator is potholing
for them, digging where the lines are supposed to be to
verify their location.
Merrell's job is to use GPR to find all the infrastructure
around these connection points if he can't locate the points
themselves. This way, the excavator knows which spots to avoid.
" They will have us out and they'll have like 30 locations at a
time where they need, essentially, a 30x30 [foot] utility locate
performed, " Merrell explained. " They have us locate everything
around the pipe they are looking for, so they don't damage any
of it when they go through and pothole to locate those lines. "
GPR continues to prove its worth as Ford inches closer to
the finish line of the multi-million-dollar project. If the excavator
were to sever a single power line while searching for the transite
pipes, it could be fatally electrocuted. The best-case scenario for
a strike is that the contractor will be looking at a costly repair job
and hours of downtime as the line is fixed.
" If I can spot the utility they're looking for, then I can save
them a boatload of money on each pothole, " Merrell said. " If I
can't spot the utility, they need to know what other utilities are
in there, so they don't bump them and make a mess of it. "
Despite its limitations, GPR continues to prove its usefulness
as the most reliable and versatile infrastructure visualization
technology. Developed nearly a century ago to measure
the thickness of ice, it has evolved to become an indispensable
tool of the construction industry.
" There's just nothing that has come along that one: can gather
the amount of data that GPR can, and two: can cover the
surface area, " Kessinger said.
" GPR being on wheels when utility locating means you
know you can scan back and forth, " he added. " It's like you're
mowing the grass. I think its ability to cover that amount of surface
area, to make it feasible to scan a large area, is what's mainly
contributed to GPR staying around as a technology. " UI
FOR MORE INFORMATION:
GPRS, gp-radar.com
GSSI, (603) 836-9663, geophysical.com
UndergroundInfrastructure.com | JUNE 2023 33
http://www.gp-radar.com http://www.geophysical.com http://www.UndergroundInfrastructure.com
Underground Infrastructure - June 2023

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