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Geotechnical News • March 2014
www.geotechnicalnews.com
GEOTECHNICAL INSTRUMENTATION NEWS
Introduction by John Dunnicliff, Editor
This is the seventy-seventh episode of GIN. Only one article this time.
Reason for only one—it’s the same old
story—despite arm twisting, you’re
being backward in coming forward.
Guidelines for articles are on www.
geotechnicalnews.com/instrumenta-
tion_news.php—see the link “How to
submit articles to John Dunnicliff for
GIN”. The first step is a 200- to 300-
word abstract.
Do you want GIN to
continue? The ball is in your court.
A newer, better way to measure
tunnel deformations
The article by Chris Fagan and
Charles Daugherty is one of those
nuts-and-boltsy contributions that tell
us about a better way to do something.
I like such straightforward articles!
International Course on
Geotechnical and Structural
Monitoring
Plans for the course in Italy in June are
almost complete. Details are on
www.
geotechnicalmonitoring.com.
After many years of courses in USA,
most recently in Florida, I’ve taken
a fresh look at what I think these
courses should include.
In addition to
the monitoring methods that we’ve
been using for many years, this course
includes innovative remote monitoring
methods such as total stations, satellite
and terrestrial radar, Lidar and GPS
- my Italian colleagues are experts at
these modern methods. The course
schedule (lecturers and topics) is on
the website
—
The Course/Schedule.
Additional information is on page 35.
Come and join us in the 10
th
century
castle! (I got it wrong in December
GIN, and jumped ahead three centu-
ries!). The wine is good, too!
Closure
Please send contributions to this
column, or an abstract of an article for
GIN, to me as an e-mail attachment in
MSWord, to john@dunnicliff.eclipse.
co.uk, or by mail: Little Leat, Whis-
selwell, Bovey Tracey, Devon TQ13
9LA, England. Tel. +44-1626-832919.
Op uw gezondheid! (Flemish: Dutch
speakers)
The Laser-Distometer: a newer, better way
to measure tunnel deformations
Chris Fagan and Charlie Daugherty
The conventional method
The conventional method of measur-
ing deformation between two points,
typically in a tunnel or excavated cav-
ern, has been to use a tape extensome-
ter. The tape extensometer is stretched
between two eye-bolts over the space
where the measurement is being taken,
the tape is tensioned correctly using
the on-board tension sensor, and the
distance shown on the tape is recorded
(Figure 1). Deformation is measured
by comparing subsequent readings
over time.
When used correctly, tape extensom-
eters will achieve accurate deforma-
tion measurements, at sub-millimeter
precision. However, in practice, the
manufacturer-claimed precision is
difficult to achieve when monitor-
ing deformation in a tunnel or cavern
that is under active construction. This
can be problematic, because the most
critical time to monitor deformation
is while construction is active, for
instance, when a tunnel heading is
advanced, or when a cavern is exca-
vated.
It is difficult to measure deforma-
tion using a tape extensometer during
Figure 1. Stretched tape extensometer.
Do you want GIN to continue? Despite arm twisting,
you’re being backward in coming forward. The first
step is a 200- to 300-word abstract. The ball is in your
court.