Making seismic connections4 November 2002
The last time ICOLD addressed seismic concerns at one of its congresses was in 1979. However, as Benedict H Fan says, seismic concerns still command attention from the dam engineering profession
AT THE forthcoming twenty-first icold Congress, to be held in Montreal from 16-23 June 2003, Question 83 will address the seismic aspects of dams. ICOLD has on four previous occasions included questions related to dams and earthquakes at its congress. In Paris in 1966, Q18 dealt with settlement of earth dams due to the compressibility of the dam materials or of the foundation and the effect of earthquakes on the design of dams. Q29, in Edinburgh in 1964, addressed the issue of results and interpretations of measurements made on large dams of all types, including earthquake observations. Istanbul in 1967 saw Q35 look at dams in earthquake zones and other unfavourable situations. Finally, in New Delhi in 1979, Q51 discussed the topic of seismicity and aseismic design of dams.
Benedict H Fan is a specialist engineer at BC Hydro Engineering in Canada and secretary for Q83. He says that dam failures in earthquakes are considered high consequence but low frequency disasters. To put the low failure frequency in perspective the following factors have to be taken into consideration:
• The reporting of seismic incidents involving dams might not be as complete as it should be.
• The level of the reservoir at the time of the earthquake is not always known.
• Without proper instrumentation data and back analyses, it is not possible to determine how close those dams were to sustaining significant and irreparable damage.
Reports of seismic dam incidents are also becoming more frequent. The following are a handful of examples:
• Several earth dams were damaged by the magnitude 7.7 Gujarat earthquake of 26 January 2001 in India.
• A gated concrete spillway was partially destroyed during the 21 September 1999 Chi-Chi earthquake in Taiwan.
• A peak acceleration of 2g was recorded at the crest of a gravity dam during the 6 October 2000 Tottori earthquake in Japan. No damage was observed from this 7.3 earthquake.
These recent events show that earthquake hazard for dams continues to demand our attention. In view of this, and the fact that 24 years will have passed since the question of dams and earthquakes was last included in an ICOLD congress, the Committee on Seismic Aspects of Dam Design successfully proposed at the annual ICOLD meeting in 2001 to sponsor a question on the Seismic Aspects of Dams for the 2003 congress in Montreal.
For Q83 papers are invited on an extensive variety of related topics:
• Dynamic material properties for concrete and embankment dams, including liquefaction phenomena.
• Observations of earthquake damage, filed measurements, laboratory tests with scaled dam models, and reservoir triggered seismicity.
• Earthquake safety and evaluation of existing dams.
• Seismic analysis problems of dams and special aseismic design features.
It is the profession's claim that well-designed dams should survive earthquakes well. With improved understanding of seismic hazards, improved analytical skills and tools, and more complete reporting of earthquake incidents involving dams, the profession is now better equipped to provide documentary and analytical corroboration to this claim. It is also now better equipped to provide practical solutions to the seismic upgrade of existing dams that are found deficient, and the aseismic design of new ones.
Dam engineering professionals are invited to attend the session on Q83 and contribute by participating in the discussions. It is important that the profession gathers at ICOLD 2003 in Montreal to share its experiences in meeting the challenges presented by the seismic aspects of dams.