Geotechnical News • September 2017
23
GEOTECHNICAL INSTRUMENTATION NEWS
Following this successful trial, instal-
lation of the remaining RATS was
undertaken, “double decking” with
existing ATS locations along the trace,
using a moving window approach to
minimise the number of RATS to be
procured.
Conclusions
Monitoring systems should be System
Checked to demonstrably prove they
meet design requirements and specifi-
cations. Dependent on the instrument
type, criteria for testing can be based
on the simulation of changes in instru-
ment position/orientation and changes
to parameters recorded.
Monitoring related problems can arise
from:
• The implicit lack of past experience
with proposed instrumentation
and/or context in which it is being
used
• Shortage of appropriately skilled
resource
• Shortages of equipment leading to
late supply and rushed installation
• Increased reliance on validation of
results and background monitoring
• Erroneous results or unforeseen
responses in use
• Potential for non-acceptance of
system by third parties (i.e. re-
assurance failure and resultant
late deployment of conventional
systems)
Undertaking a full System Check will
assist in the minimisation of adverse
effects from these problems. Omis-
sion or failure to specify or undertake
System Checks on a monitoring
system before construction activi-
ties commence can lead to inaccurate
monitoring results to the detriment of
a project.
System Checks provide informa-
tion which will assist in preventing
re-occurrences of issues on future
projects.
Whilst a System Check will assist in
providing confidence in the instrumen-
tation operation, correct positioning of
the instruments must be checked inde-
pendently as they cannot directly form
part of the process described above.
Bibliography
“Monitoring Underground Construc-
tion – A best practice guide” published
by British Tunnelling Society ISBN
978-0-7277-4118-9. Information about
this book is available on-line at www.
geotechnicalnews.com/instrumenta-
tion_news.php . Scroll to December
2011.
Glossary
Inspection and Test Plan (ITP)
A standard quality assurance require-
ment, which requires that monitoring
systems are supplied with calibra-
tion certificates, calibration checking
arrangements and specific frequencies
and protocols for such checks includ-
ing any integral processing and report-
ing software.
Method Statement
A written document that details a safe
system of work and identifies the
conceivable hazards that may arise
during the construction work. Method
statements are usually provided to the
Project Owner by the main contractor
and/or to the main contractor by the
sub-contractor(s). The Method State-
ment should explain in detail the work
that is to be undertaken and the neces-
sary measures that need to be in place
in order to protect the site workforce
and members of the public who may
be affected by the work actions.
Isabella Ramaccia and David K Cook
Mott MacDonald
8 Sydenham Road
Croydon
CR0 2EE, England
Tel +44 (0208) 774 2000
A case study of Global Navigation Satellite System (GNSS) in
landslide ground movement monitoring
Zhangwei Ning and Marc Fish
Principles of GNSS positioning
GNSS was originally designed for
precise navigation and positioning. In
recent years GNSS applications have
extended to civil and construction
industries such as surveying, con-
struction machine control as well as
structural/ground movement moni-
toring. As positioning is the core for
most GNSS applications, its underly-
ing principle is similar to a very old
surveying technique: trilateration.
Both of them rely on the measurement
of distances from an unknown point
to a certain number of known points
(control points). For trilateration these
control points are fixed points on the
earth surface, while for GNSS the con-
trol points are satellites orbiting the
earth at a speed of several kilometers
per second. As the instantaneous posi-
tion of each moving satellite on the
obit is precisely monitored and known
by the GNSS ground control sector,
the distance measurement (ranging)
is derived from the travel time of the
satellite signal transmitted from outer
space to the receiver on the earth.
GNSS signals and ranging
GPS (Global Position System) was
developed by the USA as the first
global operational GNSS. It has been
used as a synonym for GNSS until
more global or regional GNSS such as
