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Geotechnical News December 2011
GEOTECHNICAL INSTRUMENTATION NEWS
the cable, by displacing the cable
in simulation of ground strain or
by putting the cable in tension, to
gauge and record the response of
the system.
Software
The final step for achieving a fully
automatic surveillance system is the
Distributed Data Management and
Analysis Software, designed for data
storage, processing, representation,
and
analysis,
as well as for
the control of
single or multiple
reading units.
The
main
functions of the
software are au-
tomatic data ac-
quisition,
map
and graphical vi-
sualization of the
real-time strain
data along the en-
tire cable length,
and triggering of
warnings of sig-
nificant ground
displacement on
the display, as
shown in Figure
4. The software
stores all infor-
mation
related
to a sensor in a
single data-base
structure. Mul-
tiple users can ac-
cess the software
simultaneously
from different PCs (locally or remotely
over a modem or LAN).
The algorithm that supports the
software is particularly robust against
false alarms caused by outlier values
or noisy measurements. Moreover it
allows the whole system, reading unit,
and distributed temperature sensing
cable, to be insensitive to environ-
mental influences and variations. Sea-
sonal variations in temperature can be
screened out, so that they do not impact
the validity and reliability of the mea-
surements.
Besides all these capabilities, the
software is specifically developed to
send alerts in case ground deformation
exceeds a designated threshold level.
In this project, if a threshold is exceed-
ed, an alert is triggered by both e-mail
and text message to a selected list of
recipients who will respond to the re-
ceived warning by proceeding to the
site to assess whether a sinkhole may
be forming, and then take corrective
action. The recipients include key proj-
ect management, the client’s consul-
tant, and local first responders, in this
case the Hutchinson Fire Department.
In case the warning is not acknowl-
edged the software automatically sends
a reminder to the same recipients.
The software structure offers a cer-
tain level of self-diagnostic capability,
and provides data and information to
the users in an easy and fully under-
standable format.
Site Pulling Tests
In order to assess system capabilities in
terms of ground deformation detection
and alert triggering, some site pulling
tests were carried out. These tests are
aimed to evaluate and confirm the
performances of the whole final system
intended as sensor, reading unit and
data management software working
together. The idea was to apply an
external force to segments of the cable
in portions of the trench that had not
yet been backfilled, in order to induce
strain and simulate the symptoms of
ground deformation.
Figure 5. Site pull test.
Figure 6 a & b. Examples of results of the on-site pulling tests.
