breach of landslide dam - probe...

Breach of landslide dam

Overtopping of run­of­river power plants

•Mass movements into the reservoirs causing impulsive waves and blocking low level outlets.

•Power supply failure of spillway gates and shut­ down of power plants causing increase in reservoir levels as spillway gates could not be operated.

•Damage of motors (and emergency generators) for operation of spillway gates due to rockfalls

•damage of gates due to rockfalls blocking operation of gates.

Overtopping of run­of­river power plants

•Cascade of run­of­river power plants: uncontrolled release (gate failure) of water from one of the upstream power plants or dams, or failure of landslide dams.

•Flood caused by heavy rainfall was not responsible for overtopping as spillways were designed for such floods, however, a combination of a flood with some or several of the above factors may have also led to overtopping, etc.

Taipingyi Hydropower station overtopping

Jiangsheba Hydropower station overflowing

Futang Hydropower station overflowing

Yingxiuwan Hydropower station overflowing

Yuzixi powerhouse, landslide

Yingxiuwan powerhouse collapse

映秀湾厂房倒塌(Powerhouse collapse)

Taipingyi tail water outlet buried

Surface ruptures

4.7m

4.7m

6.6m

Selected seismic records

Station Wolong Qingping Bajiaotai Hanzeng

PGA (cm/s 2 )

EW 957.7 824.1 556.2 519.5 NS 652.9 802.7 581.6 350.1 UD 948.1 622.9 633.1 444.3

Epicentral distance 19 88 67 145 Distance from Longmenshan fault 23 km 3 km 10 km 12 km

Site conditions Soil Soil Soil Soil

Ongoing discussion in media

Was the May 12, 2008 Wenchuan earthquake triggered by the reservoir stored behind the 156 m high Zipingpu

concrete face rockfill dam?

The Wall Street Journal 9.2.2009 Scientists Link China's Dam to Earthquake, Renewing Debate

Reservoirs and Wenchuan Earthquake

There exists no factual evidence that supports the assumption that the devastating Wenchuan earthquake of May 12, 2008 was triggered by the Zipingpu reservoir!

Chi­Chi earthquake 1999, Shih­Kang Dam

Shih­Kang Dam:

Sheared off intake shaft due to fault movement

Manjil earthquake 1990, Sefid Rud dam, reactivated crack in bottom gallery (uplift)

Dams on faults or ‚active discontinuities‘

Potential rockfall danger for surface powerhouse

DAM SAFETY MONITORING Strong Motion Instrumentation

Strong motion instrumentation of dams

Strong motion instruments in dam

Min­. System Dam crest

Dam base

Free field

Distribution of dams with seismographs, Japan (Ministry of Land, Infrastructure and Transport)

140 dams in 1994; 413 dams in 2003

500km

Free vibration of reservoir

-6

-4

-2

0

2

4

6

0 2 4 6

Fourier s

pectrum

3 period (min.) 10

100

10

3

time (h)

Water level in reservoir cm

Natural period T= 6.5 min

Damping ratio 0.02

July 26, 2003 Miyagi Earthquake, Japan Location NS EW Vertical Distance (km)

Magnitude 5. 5 Shock Yamoto 366 476 360 cm/s 2 4.1 Naruse 603 2005 584 3.9 Kasimadai 516 489 183 7.6 Nanngou 268 229 226 6.5

Magnitude 6.2 Main shock Yamoto 667 850 1242 4.2 Nangou 366 491 193 9.9 Naruse 636 756 923 1.0 Kasimadai 1606 910 492 10.5

Magnitude 5.3 Shock Kanan 649 356 499 1.1 Nangou 276 166 126 4.9 Wakutani 255 342 130 6.9

Tokachi­Oki earthquake, Sept. 26, 2003 Effects on dams

Conclusions •Eartquake hazard is multi­hazard: rockfall hazard has been underestimatd in most places

•Dams are not inherently safe against earthquakes.

•Technology for building dams that can safely resist strong ground shaking is available.

•New safety concepts are still needed for (i) very large dams in highly seismic regions, (ii) new types of dams: CFRD and RCC dams, (iii) dams at difficult sites.

Mauvoisin Arch Dam, 250 m, Switzerland Condition of dam after successful operation for 50 Years

Grande Dixence Gravity Dam, Switzerland Highest concrete dam in world

Dam height: 285 m

Dam volume: 6 million m 3

Reservoir volume: 400 million m 3

Crest length: 695 m

Completion date: 1961

Extreme environment, Grande Dixence dam