Current Trends in Design and construction of Concrete Face Rockfill dams

Current Trends in Design and construction
of Concrete Face Rockfill dams

World wide Trend

Current Trends in Design and construction
of Concrete Face Rockfill dams

World wide Trend

Concrete Face Rockfill dams (CFRD) worldwide have become a popular choice for those dam sites in which a rockfill dam solution is selected over a concrete dam solution due to peculiar characteristics of the site. In other words, CFRDs have almost become synonymous with rockfill dam solution. Conventional Earthen Core Rockfill Dams (ECRD) are no longer preferred solutions. CFRDs have been built in different parts of the world, including the United States, Europe, Australia, Latin America and Asia. The largest numbers of CFRDS have however been built in Brazil and China.

History of Adoption of CFRDs in India

CFRDs were not quite known in India before 1997. Major rockfill dams constructed in India were all conventional earthen (clay or similar impervious material) types, including the Beas dam, Baira Dam, Salal Dam and Tehri dam. During the Design Review of the Dhauliganga Rockfill dam in NHPC in 1997 by an International consultant, the idea of a CFRD in place of a conventional rockfill dam was first mooted. Dhauliganga CFRD was to be 56 m high from the river bed.

CFRD solution was proposed mainly on three considerations:

Avoid the need for transportation of clay for clay core in conventional rockfill dam from a distance of 40 km.
Shift the location of the 60 m deep proposed cutoff wall from the centre of the dam to its upstream end.
The simplified design of cofferdams eliminates foundation treatment in cofferdams, reducing the need for dewatering for dam works

In the process of the final selection during 1997 and 1998, no. of important issues pertaining to design aspects of CFRDs were raised. During the period from 2000 to 2004, in the active construction phase of the project, J Barry Cooke and Nelson Pinto, both internationally well-known and reputed CFRD consultants, were on the panel of consultants for Dhaulinganga CFRD. All design Features and construction aspects were fully endorsed by both. Construction of the dam, face slab and the cutoff wall was successfully carried out by contractors Kajima Corporation of Japan, Daewoo construction of Korea and specialist agency Bauer from Germany. The reservoir filling took place in 2005, and the performance of CFRD was excellent to the extent that reservoir filling was a non-event, and no leakage whatsoever was noticed on the downstream face. The dam has performed well since then.

New CFRDs on alluvial foundation under construction

With the successful experience with Dhauliganga CFRD (56 m high), two more CFRDS with almost identical site conditions and similar designs were adopted in the country from 2005-2007. One of them was the 60 m high Teesta 3 CFRD on Teesta River in Sikkim. The project was on PPP model being developed by The SPV, Teesta Urja Ltd. Other CFRD was 37 m high Kishanganga CFRD on Kishanganga River in J&K. Both the projects were founded with their plinth on riverbed alluvium and plastic concrete cutoff for foundation sealing. More CFRDS on alluvial foundation under design and approval phase With the increased interest and spreading popularity, following two CFRDs, have been planned on alluvial foundations, both of which are of significantly greater height and much larger reservoir volumes.

Conclusion

Concrete face Rockfill Dams are popular dam types which have replaced the earlier adopted earth core rockfill dams. Conventional CFRDs are founded on rock foundations, which is the major trend in CFRDs worldwide. However, in India, almost all the CFRDS constructed till date follow an unconventional design with a plinth on alluvium and an upstream cutoff wall extended to rock. The Dams designed till now have been of low height and low reservoir volume; however, the concept is now being extended to Dams of greater heights and large reservoir volumes. Greater conservatism and care in design should be opted in such projects to win the confidence of the society.

DMR is a leading engineering consulting firm in India that leverages Experience and Core Expertise in Design and Engineering to offer Concept to Commissioning solutions throughout the lifecycle of projects in infrastructure sectors.

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