20
Geotechnical News •June 2015
GEOTECHNICAL INSTRUMENTATION NEWS
occasionally in the field by repeated
measurements for time intervals of
less than a few days. Also, the effects
of systematic errors, if present, have
not been identified.
The random errors/repeatability of
both types of instrument are com-
parable. They are adequate for the
purposes of settlement measure-
ments in Romaine-2 namely dam
safety assessment and modelling as
well as quantification of the effects
of increased compaction energy. The
uncertainties related to other geotech-
nical parameters pertaining to the dam
have a greater influence on these three
aspects. Differences in global accu-
racy between the SAA and INH-01 are
mainly due to systematic errors related
to the reading conditions and data
processing procedures.
Measured settlements in the
Romaine-2 dam
Installation of INH-01 and SAA took
place in October 2012 (see also Figure
3). This date corresponds to the initial
state of the instruments from which
subsequent readings are compared to
compute settlements. Figure 4 shows
a sample of measured settlements
during the construction phase of the
Romaine-2 dam.
Both types of instrument clearly show
a greater compressibility of the 3P
rockfill, as expected. April 2014 cor-
responds to the last reading during the
construction phase. This date now cor-
responds to the new initial state for the
impoundment and operation phases in
which the settlement measurements
are carried on.
Results on Figure 4 also show that
differences between INH-01 and SAA
are less than ± 1 cm which is accept-
able considering the dam height and
thus the internal stresses (up to 2 MPa)
and also, as stated before, the uncer-
tainties related to other geotechnical
parameters. Figure 5 shows a more
detailed representation of these differ-
ences. A positive difference indicates
that INH-01 measured a greater settle-
ment value than the SAA.
Differences shown on Figure 5 are
representative of random errors and
uncorrected systematic errors pertain-
ing to INH-01 and SAA.
Conclusions
Settlement monitoring of the
Romaine-2 dam is required during the
construction, impoundment and opera-
tion phases of the dam life cycle. The
analysis of the internal deformations
allows the assessment of dam behav-
iour as well as in situ materials rigidity
parameters for stress/deformation
modelling. The effects of increased
compaction energy used during
construction can also be quantified.
However, the uncertainties related to
Figure 4. Measured settlements by INH-01 and SAA.
Figure 5. Differences between measured settlements by INH-01 and SAA.
