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Geotechnical News • December 2016
GEOTECHNICAL INSTRUMENTATION NEWS
Four introductory points were made in
December 2015 GIN (
calnews.com), for Part 1 of this series
of articles, and these also apply here.
Tunnels
General role of instrumentation
The consequence of poor performance
of a tunnel can be severe and may on
occasion be catastrophic. A monitoring
programme may not be required if the
design is very conservative, if there is
previous experience with design and
construction of similar facilities un-
der similar conditions, or if the conse-
quences of poor performance will not
be severe. However, under other cir-
cumstances a monitoring programme
will normally be required to demon-
strate that the tunnel is stable and that
nearby structures are not affected ad-
versely.
Summary of instruments that can
be considered for helping to provide
answers to possible geotechnical
questions
Table 10 lists the possible geotechnical
questions that may lead to the use of
instrumentation for tunnels, together
with possible instruments that can be
considered for helping to provide an-
swers to those questions.
Table 10. Some instruments that can be considered for monitoring tunnels
Possible geotechnical
questions
Measurement
Some instruments that can be
considered
What are the initial site
conditions?
Groundwater pressure
Vertical displacement
Widths of cracks in structures
Open standpipe piezometers
Vibrating wire piezometers installed by the
fully-grouted method
(Pneumatic piezometers)
Conventional surveying methods
Remote methods
Crack gauges
Is the tunnel stable, and
are overlying struc-
tures being affected
adversely by ground
movement?
Settlement of ground surface and structures
Horizontal displacement of ground surface
and structures
Change in width of cracks in structures and
utilities
Subsurface horizontal displacement of
ground
Subsurface settlement of ground and utilities
Displacement within tunnel
Surveying methods
Remote methods
Surveying methods
Remote methods
Crack gauges
Inclinometers
In-place inclinometers
(Fibre-optic instruments)
Probe extensometers
Fixed borehole extensometers
Surveying methods
Remote methods
(Fibre-optic instruments)
