Preparation of trenches
OmniTrax Product Guide Page 109
Preparation of slots in concrete
Crossing surface cracks and expansion joints
To prevent post-installation surface damage, the cable path must cross any cracks or expansion
joints at an angle greater than 30°. If the crack or joint is deeper than 6.5 cm (2½ in.) insert a
closed foam polyethylene backer rod into the slot. Use a blunt tool to install the backer rod so the
backer rod is at least 1 cm (3/8 in.) below the bottom of the slot (just below the cable’s installation
depth). The backer rod must extend at least 30 cm (12 in.) beyond both sides of the slot, and the
backer rod must be thicker than the width of the crack or joint. See Slot dimensions
on page 111.
Note Do not cut slots if there are areas where the concrete is so thin that you
may cut through it; dig trenches. The concrete must be greater than
13 cm (5 in.) thick to cut slots.
CAUTION Long straight runs of OC2 cables in slots are NOT recommended due to
the possibility that thermal expansion can force the sensor cables to
pop out of the slots in places.
CAUTION For instances in which the sensor cables are buried in soil and pass
through concrete surface slots, the detection sensitivity over the
concrete must be tested to determine if installation adjustments are
required:
• Install the connectors on the sensor cable, but do not put on or seal
the heatshrink at this time.
• Connect the sensor cables to the processor and decouplers, and
lay the sensor cables in the trenches and slots. Do not bury the
sensor cable or seal the slots.
• Power up the processor, establish a UCM connection to the
processor, and conduct a centerline cable walk while running a
UCM response plot.
• Review the plot to determine the sensitivity over the slots.
If the average detection signal above the slots is more than 10 dB
higher than the average detection signal above the soil, then install
ferrite beads along the concrete surface at 30 cm (1 ft.) intervals.
• Once the ferrite beads are installed repeat the centerline cable walk
to verify that the adjustment is effective (the average detection
signal above the slots is less than 10 dB higher than the average
detection signal above the soil).
Note Do not route the sensor cable through existing cracks or expansion
joints in the concrete.
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