DESIGN AND CONSTRUCTION OF THE CANNELTON HYDROELECTRIC PLANT COFFERDAM AND CUT-OFF WALL-Paper

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The Cannelton Hydroelectric Project required a large cofferdam to enable construction of a powerhouse partly within the Ohio River. The facility was designed for three turbines with a total capacity of 84 MW and annual generation of about 390 GWh.<br /><br />The project reclaimed approximately 250,000 square feet of river area using a 1,300-foot marine dike, up to 100 feet tall, founded on river sediments. A cement-bentonite cutoff wall, approximately 150 feet deep and 500,000 square feet in area, extended to bedrock to limit seepage. Because the wall crossed loose underwater sand in the dike, the sand was densified by vibroflotation, with cone penetration tests used to verify improvement.<br /><br />The powerhouse excavation extended more than 105 feet below the cofferdam crest. Design analyses addressed trench and slope stability, fluctuating river levels, groundwater conditions, and deformation. A MODFLOW model informed a 20-well dewatering system, while inclinometers, piezometers, and movement points monitored performance. An emergency gate and spillway were also installed to allow rapid flooding of the cofferdam if extreme river conditions threatened its safety.<br /><br />The cutoff wall was built using a hydromill for primary panels and a clamshell for secondary panels. Equipment data systems helped verify panel alignment and continuity. A quality-control program tested 2,300 material samples for strength and permeability.<br /><br />The cofferdam performed successfully throughout construction. The wall achieved permeability better than the specified limit, and pumping averaged about 150 gallons per minute—below the predicted steady-state requirement of 400 gallons per minute. The powerhouse experienced no water-infiltration issues, and two turbines were producing power at the time of the report. The authors attribute the project’s success to detailed planning and close coordination among the design and construction teams.

Keywords

Cannelton Hydroelectric Project

cofferdam

Ohio River

powerhouse construction

hydroelectric dam

cutoff wall

dewatering system

vibroflotation

MODFLOW modeling

quality control testing