24
Geotechnical News September 2011
GEOTECHNICAL INSTRUMENTATION NEWS
Pros and Cons
The advantages and drawbacks of each
method can be summarised as shown
in Table 1.
Conclusion
Real time monitoring with RTS
has demonstrated the value of this
method for many years. Thanks to
the improvement of the range and
the repeatability of the laser beam,
monitoring of surface deformation with
RTS using reflectorless measurements
(RRTS) has become reliable, precise
and very helpful as an early warning
system, detecting movements and
trends 24 hours a day.
Generally RRTS is slightly less pre-
cise and the range is shorter than the
RTS method but for safety purposes it
is an ideal solution for dangerous sites
and an alternative to levelling measure-
ments with a high frequency of read-
ings.
Damien Tamagnan, SolData Group,
Head of survey department, Travesera
Industrial, 149 -3ª C 08907 Hospitalet
de Llobregat Barcelona (Spain).
Tel. +(34) 93 263 29 69.
email:
Martin Beth, SolData Group, Tech-
nical Manager, Rés. Maunier, 3120
Route d’Avignon 13090 Aix en Pro-
vence (France)
Tel: +(33) 4 42 21 72 11.
email :
Table 1. Comparison between the standard and the mesh method
Method
Pros
Cons
Standard Method • Fast: Time depends on
model of total station
used: approximately 5 to
10 seconds per reflector-
less measurement point.
• Simple.
• Slightly lower precision,
approximately ±1mm.
• Risk of false reading and
even false trends de-
pending on the state of
the surface.
Mesh Method
• Very high precision
in the
order of ±0.5mm
.
• Numerous security qual-
ity checks.
• Rather slow process, each
point of interest requir-
ing between 30 seconds
and 1 minute of sight-
ings.
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