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The Sondex system consists of a probe, signal cable, a
cable reel with a built-in voltmeter, and a number of stainless steel
sensing rings. A survey tape is typically connected to the probe.
The sensing rings are fixed to a continuous length of
corrugated plastic pipe which is installed coaxially with inclinometer
casing or access pipe. The annulus between the corrugated pipe and the
borehole wall is grouted. The corrugated pipe and its sensing rings settle
with the surrounding ground.
To obtain measurements, the operator draws the probe
through the access pipe. The buzzer sounds when the probe is near a ring,
and the voltmeter reading peaks when the probe is aligned with a ring. The
operator refers to the survey tape and records the depth of the ring. A
sensitivity adjustment allows operation adjacent to steel pipes, piles, or
other metal objects. Settlement and heave are calculated by comparing the
current depth of each ring to its initial depth.
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