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vertically with a strong phase of shaking of 6 s. Traces of relative movements
between blocks were observed. Cracks were also observed in the gallery operating at
half height and in the gallery foundation. Horizontal cracks of 35 to 45 m were
visible at the downstream slope change. That damage was attributed to the high
inertia of this quite unusual section, a phenomenon avoidable in modern structures.
The Kasho Dam with a height of 46 m at its base was subjected to an
acceleration of 0.53 g during the Tottori-Ken Seibu earthquake (M = 7.3) in 2000.
The peak of acceleration at the crest reached 2.00 g, with only a few cracks on the
walls and slabs of the monitoring center!
The only large dam failure is a recent one. It concerns the 25 m gate-structure
Shih Kang Dam built in 1977 in Taiwan, which broke during the Chi-Chi earthquake
on September 21, 1999. The dam has two bottom valves and 18 discharge gates. The
impressive picture of the damage is that of the concrete wall cut by the differential
movements of 9 m following the rejection of the active fault at Chelungpu, which
was sheared along a length of 105 km and shortened the valley by 6 m. The dam,
built was calculated with a seismic coefficient of 0.15. The maximum acceleration
measured nearest the site was 0.51 g horizontal and 0.53 g vertical. The reason for
failure was the vertical rejection of the reverse fault at Chelungpu; previous studies
and excavations had not revealed the position of the fault. The entire structure was
severely cracked. Disorderly displacements of the foundation layers of argillite,
siltstone and sandstone disassociated the foundations of the dam blocks. Such a
construction on an active fault is not recommended in international practice and is
prohibited in France. The difficulty here is that the fault branches in a complex
system cannot be detected by investigations. The displacement of one of its
ramifications sheared the tunnel. Despite these enormous irrecoverable
displacements, the dam was repaired and continues to be operated with a reservoir of
0.4 instead of 2.7 hm
3
[WIE 03].
10.2.2.
Earthquakeperformanceofbuttressdams
Hsinfengkiang Dam [SHE 74] in China has a height of 104 m and is supported
by 19 buttresses. In 1962, it was shaken by a 6.1 magnitude earthquake, whose
epicenter was only 1 km away. This dam developed a 82 m longitudinal crack near
the top towards the right bank and smaller cracking at the same elevation on the left
bank.
Sefi Rud Dam [AHM 92] is a 105 m high concrete gravity buttress dam in Iran
with 23 counters. It was cracked in the central part by the Rudbar earthquake on
June 21, 1990 (M = 7.6) at a time when the reservoir was 6 m below the level
downstream. The maximum acceleration was estimated to be 0.7 g at the foundation
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