Seismic Hazard and Seismic Safety of Dams Dr. Martin Wieland Chairman, ICOLD Committee on Seismic Aspects of Dam Design

ICOLD Committee on Seismic Aspects of Dam Design 26 countries

Switzerland China Japan France

M. WIELAND, Chairman H. CHEN, Vice-Chairman N. MATSUMOTO, Vice-Chairman M. LINO, Secretary

Algeria Argentine Australia Austria Canada Chile Costa Rica Egypt FYROM India Germany Iran Italy Korea Mexico Norway Pakistan Portugal Russia Serbia & Montenegro Thailand UK USA

K. BENSEGHIER J. CARMONA I. LANDON-JONES G. ZENZ B. FAN G. NOGUERA A. CLIMENT A.M. SHALABY V. MIHAILOV M. GOPALAKRISHNAN C. KOENKE A. MAHDAVIAN A. CASTOLDI Y.S. CHOI M. ROMO K. HOEG G.M. ILYAS P.S. SECO E PINTO A.N. MARCHUK A. BOZOVIC T. HARNPATTANAPANICH J.L. HINKS J.L. EHASZ

Terms of Reference of Committee on Seismic Aspects of Dam Design • Seismic safety of existing dams • Seismic interpretation of integrated observation data (strong motion instrumentation of dams) • Reservoir-triggered seismicity (RTS) • Seismic risk determination and related techniques (seismic hazard; seismic vulnerability of dams; consequences of dam failure)

ICOLD Bulletins on Earthquakes • 46 (1983): Seismicity and dam design • 52 (1986): Earthquake analysis procedures for dams (Zienkiewicz, Clough, Seed) • 62 (1988): Inspection of dams following earthquakes • 72 (1989): Selecting seismic parameters for large dams • 112 (1998): Neotectonics and dams (faults in foundation) • 113 (1999): Seismic observation of dams • 120 (2001): Design features of dams to effectively resist seismic ground motion • 123 (2002): Earthquake design and evaluation of structures appurtenant to dams

Seismic hazard – multiple hazard • ground shaking: vibrations in dams, appurtenant structures, equipment and foundations • fault movements in dam foundation • fault displacement in reservoir bottom: water waves in reservoir or loss of freeboard • mass movements into reservoir: impulse waves in the reservoir.

Usoi Dam - Lake Sarez, Pamir, Tajik. largest natural dam Landslide dam created by 1911 earthquake height ca. 650 m, freeboard 50 m dam volume ca. 2 km3

Observed earthquake effects on dams

Sefid Rud buttress dam, Iran, M = 7.5 Manjil earthquake June 21,1990

Cracks in Sefid Rud Buttress Dam

Effects of Cross-canyon Earthquake Component, Sefid Rud Dam, 1990

Transmission tower failure due to rockfall, Sefid Rud dam, 1990

Rockfall, Sefid Rud dam

Switchyard, Sefid Rud dam

Control room, Sefid Rud dam

Buildings at dam site , Sefid Rud dam

Sefid Rud dam, Repair with rock anchors

Shih-kang weir, Chi-Chi earthquake 1999

Bhuj earthquake 2001, Irrigation dams

Bhuj earthquake 2001

Upstream slide Kitayama dam Kobe earthquake 1995

Comparison of Resultant of Water Load of CFRD and Conventional Rockfill Dam with Clay Core

Nurek fill dam, Tajikistan (300 m high)

New types of dams Is this Behaviour of a Concrete-face Rockfill Dam (CFRD) Possible?

Large concrete dams subjected to strong ground shaking Reservoir-triggered seismicity • Hsinfengkiang buttress dam (1962 EQ, M = 6.1 China) • Koyna gravity dam (1967 EQ, M = 6.3, India)

‘Normal’ seismicity • Pacoima arch dam (1971 and 1994 EQ, California, 116 m) • Rapel arch dam (1985 EQ, Chile, 110 m) • Sefid Rud buttress dam (1990 EQ, M = 7.5, Iran, 106 m)

Lower Crystal Springs Gravity Dam located at San Andreas Fault survived 1906 San Francisco EQ undamaged

Lower Crystal Springs dam

Ghir arch-gravity dam, Iran, 128 m

Integral Dam Safety Concept • Structural Safety Stiffness, Strength and Ductility Deformations and Stability...

• Safety Monitoring Strong motion instrumentation, Observations Data analysis and interpretation...

• Operational Safety Rule curves and operation guidelines Experienced and qualified staff, Maintenance…

• Emergency Planning Water alarm, Flood plane mapping, Evacuation plans, Engineering back-up...

Seismic Design Criteria for Dams Operating Basis Earthquake Return period: ca. 145 years

Maximum Credible, Maximum Design, Safety Evaluation Earthquake Return period: ca. 500 (Chile) to > 10,000 years

Seismic hazard, Australia 10

Acceleration (PGA, g)

1

0.1

0.01

0.001 1

10

100

1000

Years (annee)

10000

100000

Strong motion instruments Minimum System Dam crest Dam base Free field

Inguri arch dam, Georgia, 272 m

Strong motion instrumentation

Distribution of dams with seismographs, Japan (Ministry of Land, Infrastructure and Transport) 500km

140 dams in 1994; 413 dams in 2003

2500 Earthquakes observed at dam sites Records obtained

2000 1500 1000 500

Year

2000

1995

1990

1985

1980

1975

1970

1965

0 1960

Total number of Earthquakes Total number of Records

Number of earthquakes observed and records obtained at dam sites

Kasho gravity dam, Japan

E N

Tottori Earthquake, Oct. 6, 2000 MJ = 7.3 MW = 6.6

Accelerometer in elevator shaft

0

20 40 60m

Accelerometer in gallery

Location Map of Instruments

Gallery

600 400 200 N -S -2000 -400 -600 600 400 200 E -W-2000 -400 -600 600 400 200 U -D-2000 -400 -600

Peak Acc. 0.54g 0.54g 0.49g 0

10

20

30

40

50

60

Dam Crest

Time (s) 2000 1000 N -S 0 -1000 -2000 1500 1000 500 E -W-5000 -1000 -1500 1000 500 U -D 0 -500 -1000

2.1g 1.4g 0.9g 0

10

20

30

40

50

60

Time (s)

Acceleration Records

cm 40 30 20 10 0 -10 20 cm

Permanent Displacement

N -S

27.6 cm to the North E-W

10 0 -10 -20

6.5 cm to the West

15 cm 10 5 0 -5 10

U -D

4.7 cm uplift 20

30

40

時間(sec)

Ground Displacement

50 time (s)

Water level in cm

6 4 2 0 -2 -4 -6

Fourier spectrum

0

2

4

6

time (h)

100

Natural period T= 6.5 min 10 3 3

period (min.)

10

Damping ratio h= 0.02

Free vibration of reservoir

Tokachi-Oki earthquake, Sept. 26, 2003

Effects on dams

Niigata Earthquake, Oct. 23, 2004, M = 6.8 Station

E-W (gal)

N-S (gal)

TOKAMACHI OJIYA1 NAGAOKA KOIDE NAGAOKA TSUNAMI NUMATA SHIOSAWA MIZUKAMI KASE

1850 308 706 407 369 275 293 342 279 291

1715 1147 871 521 468 397 359 342 341 237

vertical (gal)

564 820 436 312 331 86 126 127 194 63

Seismic rehabilitation of spillway on crest of Whakamaru dam, New Zealand

Rehabilitation of crest spillway Design: 0.1 g, Rehabilitation: 1.8 g

Seismic improvements of 116 dams, California 36 Temporary storage restrictions 34 Buttresses added or slopes flattened on earth dams 27 Freeboard increased 21 Outlet works rehabilitations 12 Permanent storage restrictions 11 Foundation and/or embankment materials removed and replaced 11 Foundation grouting – drainage or cutoff wall construction

General Conclusions • The technology for building dams and appurtenant structures that can safely resist the effects of strong ground shaking is available. • New concepts are still needed for very high dams in highly seismic regions, for dams at difficult sites, and new types of dams such as roller compacted concrete and concrete-face rockfill dams

Conclusions • Concrete and embankment dams can be designed to resist strong ground shaking • Modern dams shaken by strong earthquakes have performed well • Well designed concrete dams do not fail after the development of cracks • Very limited experience exists on seismic behaviour of high arch dams and new types of dams (RCC and CFR dams)

Conclusions • Strong motion instruments belong to the standard instrumentation of (i) very large dams (ii) dams with large damage potential (iii) dams located in areas of high seismicity (iv) dams showing abnormal behaviour

Next earthquake • Earthquake experience with modern dams is still very limited • After a major earthquake the guidelines for seismic design and seismic safety assessment of dams may have to be revised again!

Problems for future • Reassessment of seismic safety of existing dams and rehabilitation of dams with unacceptable seismic risk • Earthquake safety of small dams that have not been designed by engineers • Consistent use of risk-based seismic design criteria for new dams • Realistic seismic hazard assessment of dam sites to establish credible seismic parameters for design or safety evaluation