Study on the use of cellular cofferdam for permanent hydropower use

Abstract

Cellular cofferdams are temporary constructions consisting of interlocking steel-sheet piling driven as a series of interconnecting cells. Cellular cofferdams have been employed mainly as provisional “water exclusion devices” for water diversion projects to permit dry construction of dams, locks, bridge footings and piers, hydroelectric power plants, and other in-water structures. This dissertation presents the results of a comprehensive study on the potential use of cellular cofferdams as basis for the design and construction of water retaining structures to sustainably and cost-effectively harness hydropower. Cellular cofferdams have been very rarely utilized as the main permanent structure for hydropower dams. Consequently, design and construction requirements for cellular cofferdams are less stringent than for hydropower dams. To make cellular cofferdams suitable for permanent hydropower use, one design concept that utilizes cellular cofferdams as the main or core element of the water-retaining dam structure is proposed. One particular key design concept is the so-called “dry construction technique” in which the granular fill in cofferdam cells and the downstream berm are permanently kept dry in contrast to the wet construction technique for temporary use of cellular cofferdams. The viability of the proposed permanent cellular cofferdam design concept for the construction and operation is demonstrated using well-established structural and geotechnical design procedures and computational modeling. Environmental and economic impacts of the proposed cellular cofferdam-based design are studied in comparison to traditional hydropower dam constructions. The improved performance of the proposed design concept, particularly in combination with the dry construction technique, shows cellular cofferdams have the potential to be used as basis for the construction of permanent hydropower dam structures that are versatile, with less impact on the environment, and will cost less to build than conventional hydropower dams.