ABSTRACT
The upstream cofferdam for the future Jahgin RCC dam is under construction at the present moment. It is a 30 m high straight-gravity type structure that combines a first stage in conventional mass concrete and a second stage in RCC. The last portion of the RCC cofferdam will be used as full-scale trial. The original and actual design criteria are presented in the paper with special focus on the latest changes applied to simplify the structure and make possible more simplified construction methods. This has turned basic in our Project due to the lack of RCC experience of the Contractor. The aggregates that are being used for the concrete mixes are partially crushed sandstone and shales from the borrow area in the river basin. Non-plastic natural fines are used to optimise the gradation of the RCC. The result is a very workable mix, easy to handle and no segregation has been observed during the preliminary full-scale trials. The paper describes the organization of the site and procedures established for the construction of the cofferdam. Simplified transportation system by a combination of trucks and a steel chute, special forms for continuous RCC placement and grout-enriched RCC are some of the construction methods that have been experimented at Jahgin Cofferdam. The analysis and conclusions of these and other methods shall be presented as a basis for the final planning of the construction of the main dam.
