Underground Construction - September 2021 - 32

with signal reception and interpretation.
The initial BPA using Atlas Group's own
Subsite TKQ receiver confirmed it. The
TKQ is a four-frequency tracker especially
designed for larger rigs and longer bores
with a locating depth range rated to 110 feet
and tracker-to-rig range rated at 2,000 feet.
Despite the receiver's power and
accuracy, in many of the places where
Atlas crews could get signals, they couldn't
consistently trust them.
The shallow noise floor they discovered
meant even after a successful start,
portions of this job would have to be
either drilled blind or exposed. Obtaining
a visual verification at the depths specified
for this run, and working on the slopes in
rough terrain, would add enormously to
project time and cost.
Ready resource
The Woody brothers were confident
that they'd succeed in spite of the job's
complexity, but they wanted to see if
they could get better signal reliability.
They decided to bring in Subsite rep and
application specialist Brett Romer to demo
the newest HDD guidance equipment.
Romer brought a four-frequency Subsite
32 SEPTEMBER 2021 | UCONonline.com
TK RECON 4 receiver, Subsite 17T4 beacon
and Subsite Commander 7 remote display,
plus a wealth of knowledge. This enhanced
understanding of how interference affects
a receiver's interpretation and how to use
that knowledge to their advantage.
Innovations in HDD guidance systems
have made them more user-friendly and
easier to learn and operate. However,
interpreting what they say in actual field
conditions entails a much deeper grasp of
the underlying operating principles.
Romer hooked up the Commander 7
to Atlas' Ditch Witch JT3020 All Terrain
drilling rig and calibrated the receiver.
Then using both of the receivers on hand,
the team initiated another BPA, comparing
the results to the first BPA. Comparisons
are useful because they can show, for
instance, whether anomalous variations
remain consistent from one BPA to the
next, or if they have changed with time of
day or other variables. Both instruments
recommended frequencies of 29 kHz and
12 kHz to mitigate ambient interference.
Next, the crews re-examined the noise
floor for the run, determining a maximum
depth of about 55 feet. Knowing they
would not be allowed to perform locates
near the railroad tracks while running at
a depth of 35 feet, they set up the beacon
for 29 B power and 29 X power.
The 17T4 beacon Atlas was using in its
Ditch Witch Rockmaster housing on this
job was capable of emitting its signal in
four frequencies at three field-configurable
power levels. Preset frequency and power
combinations can be switched from one
to another on-the-fly by putting the
beacon to " sleep " and restarting within a
designated period of time.
Then began the drilling. One of the
benefits of the TK Recon 4 was its beacon
compass. The crew no longer needed to track
steering by having the receiver operator
cross back and forth 20 feet at a time to verify
nulls. Another benefit was its pitch-assist
tracker boot, which came into play because
of the rough, irregular terrain and varying
slope of the surfaces above the bore.
Day 2
The crew got more than halfway through
the full length of the run on the first day.
Day two's drilling would include the railway
crossings and the pass under the rebar-embedded
concrete of the old gas station's
parking lot before exiting on target.
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