Geotechnical News • June 2015
21
GEOTECHNICAL INSTRUMENTATION NEWS
other geotechnical parameters pertain-
ing to the dam have a greater influence
on these three aspects than the differ-
ences between the SAA and INH-01
measurements.
Considering this context, a SAA
represent an interesting alternative to
a conventional INH. The installation
procedures for both types of instru-
ment are similar as well as global
accuracy although the SAA appears
less prone to systematic errors. How-
ever, the SAA provided significant
advantages over INH-01 due to easier
and faster measurement, in situ check-
ing and data processing procedures.
Simple automatic data acquisition and
transmission options are also avail-
able for the SAA which can alleviate
accessibility problems and give more
flexibility in determining instrument
reading frequency.
Both INH in the Romaine-2 dam
began to show signs of malfunctioning
after less than two years of operation.
Operation of the pulley and return
cable became more difficult with time,
and ultimately impracticable due to
excessive probe and cable friction
inside the inclinometer casing and/
or the return pipe. Readings had to
be postponed until summer 2015 to
assess if these friction problems are
caused by ice build-ups. The SAA is
still performing well after nearly three
years but its long-term durability and
accuracy remain to be proven.
SAA offers more possibilities than
conventional inclinometers for mea-
suring internal deformations in dams,
since there are no series of casings to
install and to access later for read-
ings. A series of six horizontal SAA
cables will be installed in a 92 m-high
embankment dam to be constructed
in 2015 and 2016 to monitor settle-
ment in the upstream and downstream
rockfill shoulders
The Romaine-2 experience has shown
that a SAA installation can have
higher initial hardware costs than a
conventional inclinometer. However,
these costs can be recouped in a longer
term considering reading and data
processing time, instrument accessibil-
ity as well as durability.
Both types of instrument, SAA and
INH, provided useful results for
Romaine-2 but the SAA did so more
conveniently, with more flexibility
and, apparently, for a longer period of
time.
Marc Smith
Hydro Québec
Dam Safety Division
75 René-Lévesque west, third floor
Montréal, Québec, Canada
H2Z 1A4
Tel. 514-289-2211 ext. 5162
E-mail:
Discussion of
“
The fundaments of wireless monitoring –
things to consider
”
by Simon Maddison.
Geotechnical News, Vol. 32, Number 4, December 2014
Adam Dulmage and Matt Trenwith
This is a very useful article when
considering data acquisition options
for geotechnical monitoring (or any
application for that matter). We have
direct experience with mesh networks
in mining environments, primarily
underground, but also many surface
applications, and we will touch on
some of the lessons learned in these
harsh environments.
The term
‘
wireless
ʼ
In many cases, the term ‘wireless’ is
used interchangeably with ‘Wi-Fi’ -
so let’s clarify this point first (as this
tends to be a hot topic with mining
companies right now). ‘Wireless’ can
be any type of technology that does
not use wires for communication.
It can use any range of frequencies,
bandwidth, protocol, antenna type,
etc. It is a very generic term. ‘Wi-Fi’
is much more specific and is defined
as any wireless local area networking
product based on the IEEE 802.11
standard. This is what most home
wireless networks are built upon -
your computer and your cell phone
typically have a Wi-Fi radio built into
them. ‘Wireless’ as it relates to geo-
technical monitoring is almost always
NOT Wi-Fi, but often a purpose built
sensor network designed just for data
acquisition and monitoring of (typi-
cally) low power sensors.
Frequency selection
So, onto the good stuff. Talking about
frequencies — 2.4GHz is generally
license-free worldwide, and 900MHz
is license-free primarily in North
America and Australia, so this needs to
be considered at the beginning of the
project. However, additional restric-
tions may be imposed by the mining
firm, especially in blasting zones.
There is also a significant difference in
signal propagation between 900MHz
and 2.4GHz. 900MHz is more for-
giving, allowing non-line-of-sight
