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and 2.8 g at the crest. It was calculated to have no traction on the upstream face
under a pseudo-static coefficient of 0.1 and allowable stresses, less than 7 MPa in
compression and 0.7 MPa in tension. The dam performed well during and after the
earthquake, despite several cracks in the upper part [ZAK 03]. These cracks were
concentrated in three locations: at the junction of the central buttresses and the wall;
in the central buttresses at the construction joints; and at the joints between the
buttresses. A horizontal crack opening a construction joint spanned 24 buttresses.
Although a triangular wedge was formed under the buttress head, the maximum
displacement did not exceed 2.5 cm. (see Figure 10.4). The separate parts of the
buttresses underwent only small rotations without slipping. Vertical expansion joints
were damaged and some leaked, but the leaks did not increase with time. A sharp
drop in uplift was recorded at the base of the dam; on the other hand, leaks occurred
downstream of the horizontal cracks, running through the plot. Despite the existence
of horizontal cracks, the large accelerations, and the fact that the cracked buttresses
could move freely in an upstream−downstream direction, no significant horizontal
motion was observed. In the meantime, some indirect effects, which may lead to
breakage in other circumstances, have been reported. The leak of the drainage
gallery, from the opening of a crack at the location of a fault, increased over time.
Numerous rock falls on the roads nearby, including the banks, have suspended
traffic. Several power poles were cut down. The control room of a factory was badly
damaged.
10.2.3.
Earthquakeperformanceofarchdams
On February 9, 1971, the Pacoima Arch Dam was subjected to the San Fernando,
CA, earthquake (M = 6.5). The arch dam was located about 6 km from the epicenter
of the earthquake. This arch, built in 1929, has a double curvature and a height of
113 m. An accelerograph, placed on the left bank at 40 m distance and 15 m above
the crest, recorded an unprecedented peak acceleration of 1.25 g horizontal and
0.70 g vertical. The reservoir was 45 m below the crest. The arch was able to bear
the shock, which indicates a margin of safety inherent in this type of structure. Yet
the valley had narrowed by more than 2 cm. The greatest damage observed was the
opening of a 6 mm to 1 cm contraction joint along a length of 15 m between the arch
and the thrust block on the left bank and cracking of the block for a length of 2 m.
During the Northridge earthquake, the only effects recorded on arch dams were a
few openings in the vertical expansion joints after several cycles of opening and
closing.
It is essential to analyze the movements of joints between blocks, for they
dissipate energy and unacceptable tensions appear in a numerical model without
joints [ARI 03]. After validating the 3D model attached to the Shintoyone Dam,
where a maximum acceleration of 1.0 g was recorded on the crest in 1997 during an
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