Geotechnical News September 2011
21
GEOTECHNICAL INSTRUMENTATION NEWS
surveyed using a second probe through-
out construction projects. These data
were used to build our database.
Study Specifics and Results
Consecutive surveys (A0/A180 data
only) were taken with only one probe
at two types of installation:
• Borehole installations use ABS
casing backfilled with grout into a
hole in a suspected zone of ground
movement.
• Attached installations use ABS cas-
ing attached to piles or rigid struc-
tures and backfilled with grout into
a caisson wall.
The readings collected were com-
pared and all found to be repeatable
to both our criteria and the manufac-
turer’s specifications.
Further consecutive surveys again
(A0/A180 data only) using as few as
two probes or as many as four probes,
were compared for repeatability, with
the flowing results:
• Borehole installations. Figure 1
shows 26 surveys. As can been
seen, 17 were repeatable within our
criterion and 23 met the manufac-
turer’s specifications, representing
65% and 88% respectively.
• Attached installations. Figure 2
shows 283 surveys. As can be seen,
248 were repeatable within our cri-
terion and 280 met the manufac-
turer’s specifications, representing
88% and 99% respectively.
Conclusions
Borehole installations represent 10%
of Monir’s inclinometers. Typical
borehole installations are more out
of plumb, have more undulations and
undergo more movement than attached
installations, and we believe that this is
the reason for the poorer repeatability.
As attached installations on piles for
excavation support are the majority of
Monir’s installations, we plan on contin-
uing to focus our attention on these.
Based on the results of this study,
Monir will consider probes to be inter-
changeable for attached installations
to the manufacturer’s specifications.
We will however strive to implement
procedural improvements which will
achieve the same repeatability for our
criterion.
Brian Tigani and Rolando Rongo
Monir Precision Monitoring Inc.,
Mississauga, Ontario, Canada,
L5J 4S9, Tel. (905).822.0090,
emails:
and
Monitoring of Surface Deformation with
Robotic Total Stations Using Reflectorless
Measurements
Damien Tamagnan and Martin Beth
Introduction
Real time monitoring using Robotic
Total Stations (RTS) over tunnel
excavations in the proximity of
diaphragm walls or other construction
generally includes monitoring of
buildings and ground movements.
The challenge in the case of roads and
pavements is to leave the site free of
any obstacles and to observe surfaces
automatically in order to respond to
real time monitoring criteria, without
installing sensors. The aim is to avoid
problems caused by the interruption of
traffic and above all, for safety reasons,
the danger of making traditional
manual topography measurements on
an active road.
New generations of robotic total sta-
tions allow Reflectorless Surface Point
Figure 1. Survey repeatabilities with multiple probes for bore-
hole installations.
Figure 2. Survey repeatabilities with multiple probes for
attached installations.
