75th Anniversary |
Above: Sefid Rud buttress dam damaged by the 1990 Manjil- Rudbar earthquake in Iran: irrigation outlets were opened to lower the reservoir after the earthquake
Below: ICOLD-CHINCOLD reconnaissance mission after the 2008 Wenchuan earthquake in China; joint opening at the crest of the 156 m high Zipingpu CFRD
of the Himalayas, crosses the dam site. In 2005 the Muzaffarabad earthquake with a magnitude of 7.6 occurred at another fault in this region. As the MBT could produce significant earthquakes, the ground motions observed during the Muzaffarabad earthquake were taken as a reference for the design of the concrete dam. For the dam design and the safety-critical elements (e.g. spillways) the horizontal peak ground acceleration of the safety evaluation earthquake was taken as 1.25g as well as an almost vertically dipping fault offset of 3.6m. Because no concrete dam can be designed to withstand fault movements and since the excavation of the MBT showed that it has a width of several metres, in which fault movements could occur anywhere, it was decided to construct a conservatively designed earth core rockfill dam across the MBT fault zone, which may be considered as a kind of “slip joint” that can absorb possible fault movements without failure. In addition, some fault treatment by means of weakening the rock using closely spaced bentonite filled boreholes was necessary to prevent fault movements occurring below the concrete dam. I could also mention my involvement in the
international team inspecting the 106m high Sefid Rud buttress dam, which was damaged by the magnitude 7.4 Manjil-Rudbar earthquake in the Alborz Mountains in Iran in 1990. The epicentre of this devastating earthquake causing the loss of about 45,000 lives in the dam region was assumed to be only a few hundred metres away from the dam, which suffered different types of damage and had to be repaired and strengthened after the earthquake. Sefid Rud dam is the concrete dam, which up to now, has experienced the strongest ground shaking of any concrete dam and, therefore, serves as a reference for assessing the possible effects of a strong earthquake on gravity dams. Furthermore, following the magnitude 7.9
Wenchuan earthquake of May 2008 in Sichuan Province in China, together with CHINCOLD, I led an ICOLD reconnaissance mission to various dams damaged by this catastrophic earthquake. This earthquake damaged about 1800 dams and reservoirs and 400 powerhouses.
The two most important dam projects affected by this earthquake were (i) the Zipingpu concrete-faced rockfill dam with a height of 156m, whose construction was completed only two years before the earthquake, and (ii) the 132m high Shapai RCC arch dam, completed in 2004, which was the world‘s highest RCC arch dam, did not suffer any damage.
Technical challenges There are technically very challenging dam projects
in different parts of the world, but it seems, based on my experience, that sites in the Himalayan Mountain Range including the Himalayas, Karakorum, Hindukush, and Pamir need special attention, as besides strong earthquakes there are numerous glacial lakes, which may create large glacial lake outflow floods (GLOFs). Other hazards include rockslides, cloud bursts, etc. Some GLOFs, rockslides and ice avalanches and associated debris flows may be that large, that dams with small storage may not be safe and should not be built. However, in the case of GLOFs prevention measures could be taken to lower or drain the glacial lakes and warning systems could be installed. Dam engineering, because of its high safety
requirements, has contributed much to the field of civil engineering and beyond. For example, most people may not be aware of the fact that the finite element method, used for the numerical analyses of structures etc, was developed by R. Clough and O.C. Zienkiewicz, who were involved in the static and seismic analysis of concrete dams and published the ICOLD Bulletin on Earthquake Analysis Procedures for Dams in 1986. Clough created the term “finite elements” in the 1960s and already in 1962 he published a paper on “Stress Analysis of a Gravity Dam by the Finite Element Method”, which shows that dams played an important role in the development of this very versatile numerical analysis method. Besides technical safety, which takes precedence over any other issues, there are newer aspects that have an impact on the development of water resources. The main future concern is biodiversity. Biodiversity is unique at each dam site; this is true for any dam project. Also the effects of climate change are of increasing concern, attracting a lot of attention; however, these are mainly related to the operation of the reservoir than to dam safety, as in the case of dam safety there exist long- established procedures to cope with time-dependent and new types of hazards. The concept used is quite straightforward and requires a periodic safety review, which includes a detailed inspection of the dam and a review of the design and safety criteria. Such reviews could be done every five years. Finally, as a civil engineer having worked on different types of civil engineering projects, I would like to point out that dam projects are the most interdisciplinary and challenging civil engineering projects, in which civil engineers still play the main role. Therefore, I can strongly recommend any young civil engineers to work on such projects.
Left: Ray Clough, the inventor of the Finite Element Method, together with Martin at the International Workshop on Arch Dams, Coimbra, Portugal, April 1987
26 | May 2024 |
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