Experiments on Large Structures - Dynamic Behavior of Concrete and Seismic Engineering - page 228

6.6.3. Study of the effect of the water level inside the reservoirs
Dynamic test techniques can be used to study the effect water level inside
reservoirs has on the dynamic response of concrete dams. A multiple test campaign
was completed on a large dam in Switzerland, as part of a collaboration between the
Swiss Federal Water and Geology Office, Electricité de France, Hydro-Quebec and
Emosson S.A.
Forced vibration measurements were carried out on the Emosson arch-dam,
located on the French-Swiss border near Martigny. This 180 m high arch
(represented by a finite element model in Figure 6.22) was submitted to forced
vibrations by an unbalanced mass exciter, and the hydrodynamic pressure and
acceleration responses for different water levels in the reservoir were derived [PRO
01].
The yearly variations of water levels inside the reservoir are shown in Figure
6.23. The test periods - there were four of them were chosen with “empty” and
“full” lake conditions, plus two intermediate levels. Access to the dam, which is
located in an Alpine region, is limited by a snow covering which generally still
prevails in spring during the empty reservoir conditions. The reservoir fills up in
summer, and usually reaches its maximum operating level (roughly 225 x 10 3 m 3 ) in
September.
Dynamic tests were conducted in a way similar to those described in the previous
section. The frequency responses enabled several resonance values within
frequencies ranging from 0 to 10 Hz to be identified, and derivation of the
corresponding modal damping.
180 m
Figure 6.22. Model of the Emosson arch-dam