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Geotechnical News • March 2016
GEOTECHNICAL INSTRUMENTATION NEWS
that, in the end, levels the professional
playing ground.
As for Martin’s comments on figures,
we agree that a large number of factors
affect the precision of the RTS data
in a real-life monitoring environment.
Regarding Figure 3, the RTS was posi-
tioned well within the monitoring zone
and with some less than ideal configu-
ration for the monitoring targets. For
example, the vertical angle and orien-
tation was such that during daytime
hours glare from the sun was an issue.
Accepting the facts of the locations
required to provide the monitoring, the
precision of the data shown exhibits a
standard deviation of approximately
0.035 inches. As the manufacturer’s
stated precision for distances measure-
ment is 1 millimeter or 0.039 inches,
the precision is within the parameters
of the instrument. It has long been our
view that extensive data-smoothing
should not be employed on raw
data used by the RTS specialist and
the engineer should review the site
conditions to determine plausibility
of actual movement. It has also been
our experience that after significant
movements are experienced, as shown
in the figure, the system precision may
be slightly degraded as the original
orientations of the monitoring prisms
to the RTS has been changed.
Finally it is also important to dis-
cuss that, as Martin note
s,
Figure 4
does not provide a proper geometric
layout for the RTS system. We feel
it is important for readers to under-
stand that some systems cannot be
designed ideally. This figure presents
a particularly challenging situation
where monitoring was required over
a long-span bridge across a body of
water, which required extensive design
to the system to improve the robust-
ness of the data quality. We consider
the design of the system in this figure
to be a prime example of incorporating
different backgrounds, skill sets and
experience levels into the design of a
monitoring system, and the complex-
ity often required may not be found in
a single easily defined individual.
Joel Volterra
Joel starts his discussion with a topic
also brought up by Martin, and one
we wanted to avoid, that the RTS
specialist should be a technician. It
was not our intention to discuss the
qualifications of the Geotechnical
Instrumentation Engineer or state that
the monitoring system as a whole
should be designed and overseen by
the RTS specialist who we attempted
to describe. Luckily we realign with
Joel as he further goes on to discuss;
depending on how the project is man-
aged the data interpretation and data
management should be undertaken by
personnel that not only understand the
reason for movement but the evolving
technical nature of RTS data.
Again, it goes back to the argument
that this work should be undertaken
by a very small subspecialty of PEs
or PLSs who have obtained, through
project experience or formal training,
the qualifications to undertake the
work. This brings us back to the point
regarding the requirement for having
a licensed professional making this
determination regarding their own
qualifications regardless of the specifi-
cation language.
Maybe the answer is that the specifica-
tions should be written by someone
(PE or PLS) who has the same or simi-
lar project experience.
Douglas Roy
GZA GeoEnvironmental, Inc.
104 West 29
th
Street, 10
th
Floor
New York, NY 10001
212-594-8140
Email:
Jonathan A. Stuhl
DPK Consulting, LLC
147 Union Avenue, Suite 1C
Middlesex, NJ 08846
732-764-0100
Email:
General role of instrumentation, and summaries of instruments
that can be considered for helping to provide answers to
possible geotechnical questions. Part 2.
John Dunnicliff
Introduction
This is the second in a series of
articles that attempt to identify:
• The general role of instrumentation
for various project types.
• The possible geotechnical questions
that may arise during design or
construction, and that lead to the
use of instrumentation
• Some instruments that can be
considered for helping to provide
answers to those questions.
Part 1, covering internally and
externally braced excavations, was in
December 2015 GIN.
Part 2 covers embankments on soft
ground.
