The main structure is a 3,270-ft-long, 620-ft-high hollow concrete gravity dam. Although the dam contains 7.9 million cu yd of concrete, the design was chosen because it required 35% less concrete than a solid gravity dam.

At the dam's base is a 3,114-ft-long, 357-ft-high powerhouse. On the right, the dam tapers into an abutment dam that ties into a concrete buttress structure carrying the spillway. A 2,600-ft-long earthen dam links the spillway with the Paraguayan riverbank. The other side of the dam is linked to Brazil by a 3-mile series of earth and rockfill dams.

The diversion channel alone was a major project. The Parana has an average flow of 293,000 cu ft per sec and never before had such a large river been fully diverted. It took almost three years to excavate 25 million cu yd of rock to cut the 1.3-mile-long, 300-ft-deep, 490-ft-wide channel.

The two cofferdams protecting the construction site were 328 ft high and 1,800 ft long, among the largest ever built. Each was a rock embankment enclosing a clay core that was at least 148 ft wide at the base.

Concrete placement on the dam, spillway and powerhouse averaged 365,552 cu yd per month and peaked at 440,554 cu yd. This was made possible by use of seven cableways fed by monorails from three large batch plants on each abutment, eight rail-mounted tower cranes and five 290-ft-tall gantry cranes. The six batch plants had a total capacity of more than 1,400 cu yd per hour.

To speed concreting of the powerhouse, all the upper portions above the embedded draft tube and penstock
sections were slipformed instead of cast in place as specified in the design. Slipforming did the job in seven months, instead of the 12 months allotted for cast in place.

The project's feasibility study and some design was performed by the engineering arm of Morrison-Knudsen Corp. and Italy's Electroconsult, SPA. That venture acted as technical coordinator. Brazilian and Paraguayan engineers handled most of the design and a consortium of local firms, Union-Conempa, built the project.

Itaipu impounds a reservoir 125 miles long that contains 23.3 million acre-ft of water. Impressive as Itaipu's capacity is, the complex will eventually lose its hydroelectric generating record to China's 18,200-Mw Three Gorges Dam and Russia's 20,000-Mw Turukhansk Dam.

Japan's Sinking Airport
Japan's artificial island in Osaka Bay that was to hold the $7.7-billion Kansai International Airport was sinking at a much faster rate than originally anticipated. The 1,263-acre island was built in 59 ft of water on top of a soft, water-saturated alluvial clay layer 66-ft thick and a diluvial layer of clay beneath it with sand lenses about 1,000 ft thick. Though geologists presented a wide range of possible total settlements, the project's engineers based their design on the optimistic end of the range because of budget pressures and the little that could have been done to speed settlement. Because of the increased settlement, engineers estimated that consolidation would be two to three times greater than expected within the diluvial layer, so they decided to increase the depth of fill by 11 ft, making it 108 ft (ENR 1/7/91 p. 9).

Recession Paranoia and War
As war escalated in the Gulf in 1991, many professionals in construction braced for an industry slump that was expected to last a few years. The crisis aggravated the "industry recession jitters" that were already felt throughout construction. Though the recession was considered the key roadblock to construction recovery, tight credit, commercial overbuilding and public works financing compounded the problem. Economists speculated that even after a recovery, builders and developers seeking capitol would still find banks unwilling to make loans. One economist speculated that the 90s would be a disappointing decade: "the decade after" (ENR 1/28/91).

The Boston Harbor Cleanup
The Massachusetts Water Resources Authority's effort to clean up one of the country's most notoriously polluted waterways in the country got under way in 1991. Contractors began to bore a 9-mile-long, 24-ft-dia. outfall and three smaller tunnels that were to feed sewage flows and utility lines to the new $78-million, 1.2-billion-gal-per-day wastewater treatment plant where 145 dry tons of sludge per day would be converted to fertilizer. This would allow MWRA to finally halt the discharge of sludge into the harbor. In the midst of an economic crisis, the project was good news for the state of Massachusetts, as generous funds would compensate 2,500 workers at peak. MWRA's program director noted that the Harbor Cleanup was "the only game in town," therefore attracting "the cream of the state's workers" (ENR 10/21/91 p. 28).