Geotechnical News • December 2016
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GEOTECHNICAL INSTRUMENTATION NEWS
rock mass displacement mechanisms.
Research is on-going to establish AE
signatures that can be used to warn of
instability as increasing AE rates could
be related to accelerating damage
events at the micro-scale as precursors
of a macroscopic brittle failure.
Acknowledgements
The support provided by the Engi-
neering and Physical Sciences Re-
search Council (EP/H007261/1, EP/
D035325/1) is gratefully acknowl-
edged. The authors also acknowledge
the collaboration with Philip Meldrum,
British Geological Survey, in develop-
ment of the AE measurement system.
Reference
Cruden DM and Varnes DJ (1996)
‘Landslide types and processes’,
in KA Turner & RL Schuster
(eds), Landslides—Investigation
and mitigation: Transportation
Research Board Special report no.
247, National Research Council,
National Academy Press, Wash-
ington, pp. 36–75.
All authors,
School of Civil and Building
Engineering,
Loughborough University,
Leicestershire, LE11 3TU, UK
Alister Smith,
Tel: +44 (0)1509 565179,
Email:
Neil Dixon,
Tel: +44 (0)1509 228542,
Email:
Daniela Codeglia,
Tel: +44 (0)1509 228542,
Email:
.
Gary Fowmes,
Tel: +44 (0)1509 223775,
Email:
.
Monitoring a heritage building restoration project
with geotechnical instrumentation
Vincent Le Borgne
Introduction
2017 will mark the 150th anniversary
of the Canadian Confederation. Amidst
the preparations for the celebrations,
infrastructure projects have been un-
dertaken, including major work to
modernize, both structurally and es-
thetically, the 150-year old West Block
Building in Ottawa while maintaining
its heritage appearance (depicted in
Figure 1). The project required ex-
tensive monitoring with geotechnical
instrumentation. The structural work
requiring instrumentation had three
phases:
1. Backfilling of abandoned tunnels
2. Excavation of the inside of the
north wing to add new basement
floors
3. Excavation of the inner courtyard
to add new basement floors
An overview will be provided of what
to be aware of regarding instrumenta-
tion, and some issues that arise from
working in a demolition-related proj-
ect. Additionally, there will be specific
examples regarding the effects of tem-
perature and the importance obtaining
and generating proper baselines.
Settlement system
Purpose and description of
instruments
During Phase 1, tunnels running under
the building were reinforced and back-
filled. Because this phase could induce
significant differential settlement, a
highly sensitive settlement measure-
ment system was installed (Geokon
model 4675). In this system, the sen-
sors are connected to each other with
liquid-filled flexible tubing. Each sen-
sor measures the liquid level within its
housing. The liquid level difference
with respect to a reference sensor is
equal to the differential settlement
value
Sources of inaccuracy
Temperature variations create chal-
lenges. Since these systems measure
differential liquid levels, temperature
changes at one part of the system will
alter the specific gravity of the liquid
locally, inducing inaccurate readings.
In addition to temperature, the pres-
ence of air bubbles can severely impact
the quality of measurements. Indeed,
air being a compressible fluid, it can
“dampen” shifts in position of the wa-
ter containers and yielding unreliable.
Figure 1. Picture of Parliament Hill’s
West Block in Ottawa.
