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Geotechnical News • September 2013
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GEOTECHNICAL INSTRUMENTATION NEWS
failures of thermistors and a piezome-
ter below this depth, we suspected that
a few INC500 sensors were damaged
in the shear zone. The manufacturer
of the device agreed, indicating that
the sensors “probably deformed or
rotated within the housing” (J. Lemke,
pers. comm., Nov. 2012). The M-IPI
continued to record downslope motion
above the shear zone, with episodes of
“retrograde motion” intermixed (see
Figures 4b and 4c). Then on October
31, the INC500 sensors below 20.2
m bgs ceased reporting data. The
manufacturer suggested that either
the cable was physically severed or
that an underwater connector between
modules pulled apart (J. Lemke, pers.
comm., Dec. 2012). The sensors above
the shear zone, however, continued to
report movement and temperature data.
Scheduling allowed the author
and colleagues to return to the site
every two to three weeks for manual
inclinometer probe measurements.
Considering the movement rate, only
one or two additional sets of readings
would have been obtained before the
inclinometer probe could no longer
pass the shear zone. Thus, the M-IPI
device at this site delivered much
more data than we otherwise would
have collected.
The M-IPI device provided addi-
tional data in another way. Figure 5a
contains a temperature profile of the
boring. Thermistor measurements col-
lected on September 29 demonstrated
elevated temperatures due to the drill-
ing process (having not yet reached
a pseudo-equilibrium). Most of these
temperatures, however, fit the trend
that developed with depth during the
equilibrating process, with the excep-
tion of the malfunctioning thermistor
at 25.9 m bgs. All thermistors and the
VW piezometer below 18.3 m bgs
failed on October 11 and October 26,
respectively. Starting on November
9, the lowest remaining thermistors
began reporting a steady increase in
temperature resulting in above-freez-
ing values, as indicated by the erratic
temperature profile from November
23; yet the VW piezometer located
at 16.3 m bgs (i.e., “P1”) measured
-1.3ºC, matching the previous tem-
perature trend. Figure 5b is a plot of
temperatures obtained from the M-IPI
device. The M-IPI stopped report-
ing accurate temperatures below 20.0
m bgs on October 24; however, the
data above this depth are sufficient to
indicate below freezing temperatures.
Thus, the M-IPI data confirmed that
the thermistors below 4.6 m bgs began
to malfunction on November 9, likely
the result of propylene glycol entering
the cable and affecting the measured
resistance.
Conclusion
The in situ measurements from the
Dalton Highway site indicated that
FDL-A moved at approximately 2.5
cm per day during the measurement
period, more than twice the historic
rate. The M-IPI device continued to
read during shearing and provided
meaningful temperature data after
shearing. Its presence in the continu-
ally moving landslide provided much
more data than we otherwise would
have collected due to the remoteness
of the site. The M-IPI temperature
readings served as a check of poten-
tially faulty readings from other
temperature sensors, an unexpected
benefit of this device.
Acknowledgements
This project was jointly funded by
ADOT&PF and the Alaska University
Transportation Center. The author
thanks her UAF colleagues and
ADOT&PF personnel for their exper-
tise, hard work in the field, and sup-
port; and J. Lemke for his willingness
to address concerns and his patience
with insistent questions.
References
Cornforth, D. H., 2005. Landslides
in Practice: John Wiley and Sons,
Inc., Hoboken, NJ.
Daanen, R. P., Grosse, G., Darrow,
M. M., Hamilton, T. D., Jones, B.
M., 2012. “Rapid movement of
frozen debris-lobes: implications
for permafrost degradation and
slope instability in the south-
central Brooks Range, Alaska.”
Natural Hazards and Earth System
Science: 12:5, 1-17, doi:10.5194/
nhess-12-1-2012.
GEODAQ, Inc., 2010. INC500 Series
In-Place Inclinometer datasheet:
GEODAQ, Inc., Sacramento, CA.
Margaret M. Darrow
Associate Professor, Dept. of Mining
and Geological Engineering,
University of Alaska Fairbanks,
Fairbanks, Alaska,
T. +1 907 474 7303,
E: mmdarrow@alaska.edu
Lessons learned from unexpected events in the field
Anonymous
Introduction
This contribution is in response to
John Dunnicliff’s repeated plea, “Les-
sons learned. I need you”.
Field monitoring may require special
installations or simple visual inspec-
tions to determine whether specified
criteria are met or there is need for
corrective action. The examples of
problems encountered with light-
ning and with inadequate planning
of observations for a cofferdam on
the foreshore of a lake are described.
Some unusual water levels are noted.