The Dutch reaction was the Delta Project, which would build a system of dams to close off the mouths and inner reaches of the interconnected inlets that had long been the victims of the North Sea.

The Rijkswaterstaat, the public water authority, initially set out to build five primary and five secondary dams to a level 3 ft higher than the 1953 flood. This 18.5 miles of dam would shut out the sea entirely, but both environmentalists and fishing interests balked at closing off the Eastern Schelde estuary. The compromise was a storm barrier across the 5.6-mile estuary inlet that would keep the sea's usual tidal flow intact but be able to close it off when flooding threatened.

The storm surge barrier is made up of 66 prefabricated and prestressed-concrete piers placed without piling on the seabed and equipped with 63 sliding gates. The barrier extends 2.8 km across three channels formed by two work islands and a 128-ft-high dike.

The piers, 148 ft high and weighing 18,000 tons, were cast in a construction dock. Their bases linked by concrete box beams, the piers were carried into place by a specially designed ship. Although sited in 100 ft of water, they had to be positioned to within 12 in. of their design location. Steel gates between the piers are 17 ft thick, 130 ft wide and vary in height from 77 to 155 ft. The piers were embedded 35 ft in the sea bottom. To prepare the site, the bottom was dredged, replaced with 3 ft of clean sand, and compacted to depths of 50 ft, using vibrators. To keep the fine sand from washing away, two mats made of steel-reinforced plastic material were placed one atop the other under each pier. The lower mat, 15 in. thick and measuring 650 x 140 ft, consists of layers of sand, fine gravel and coarse gravel. The top mat, 200 x 100 ft, is made up of three layers of coarse gravel. Around the base of each pier are graded layers of stone, the topmost made up to 6 to 10-ton basalt rocks.

The project estimated cost was $1 billion when approved in 1976. However, the switch in its scope from a dam across the Eastern Schelde estuary to a barrier raised the final price to $2.4 billion. But the project proved itself in 1990, holding off a flood of potentially disastrous proportions.

Quake Brings New Knowledge
The Mexico City earthquake of 1985, which measured 8.1 on the Richter scale, killed over 30,000 people. At an international conference one year later, seismic engineers talked about the lessons learned there (ENR 9/4/86). Instrumented buildings provided records of strong ground motion in soft soil for the first time. Engineers were surprised by the degree of acceleration, 0.18 g acting laterally, in the soil of the former lake bed, which slowed the frequency of shock waves transmitted 250 miles away at the fault lines of Mexico's West Coast. Also surprising was that only 1.5% of the engineered buildings in the most affected zone were severely damaged. But the number of dramatic collapses of tall buildings was thought to be the highest in the recorded history of earthquakes. As a result, new emergency codes were implemented.

Building a Grave for Nuclear Waste
The project that was to be the final resting place for nuclear defense waste got under way in 1986. The U.S. Dept. of Energy's Waste Isolation Pilot Plant in southeastern New Mexico was proposed in 1975 for disposal of spent fuel rods from commercial reactors, but it was delayed by political upset. The ancient 2,150-ft-deep salt beds, provided wipp with 6.2 million cu ft of waste storage capacity. It was expected to expand to 95 million cu ft to accommodate wastes from dismantled doe weapons reactors. Officials later discovered an even better disposal site 500 ft below in the same ancient seabed, but it was to be reserved for burial of the military's most potent radioactive by-products (ENR 6/12/86 p. 20).

Computers: The New Construction Tool
An increase in personal computer use and a trend toward more integrated construction computing in the mid-1980s led ENR to hold an "electronic symposium" (ENR 9/25/86). Participants included information officials from construction firms around the country. Previously, "project managers' needs took a back seat because all that really existed was financial accounting software," said an executive at Mellon Stuart. "Now the information needs of the project manager drive [the firm's] is." Topics for discussion in the 17-day session included the latest trends in management information systems, software and the demand for more powerful machines. For example, one participant with an 8-Mb, 12-Mhz at offered to race another with a 600-K at. But the second said his machine wouldn't "hold a candle."