Bogged down

Far beneath the waves and the bay's bottom, the test borings uncovered evidence of another formidable obstacle.

Sandwiched in the clay 70 feet below the north edge of the Thimble Shoal channel was a 50-foot-thick layer of soft, potentially unstable peat that posed significant problems for the construction of the first tunnel's north island.

Draining and compacting the underground bog took six months, with crews driving more than 3,800 steel pipes 100 feet into the bottom in order to release the trapped water. Then they piled up thousands of tons of extra sand, squeezing the spongy deposit into a hard, firm stratum.

That hard-won success didn't come without a deadly cost, however.

"When you put a big steel pipe 100 feet into the ground, you're dealing with some pretty strong forces when you pull them out," Fowler says, his voice becoming solemn.

"One of them buckled the crane boom and killed two men."

Hard start

Despite the tragedy, the construction of the Chesapeake Bay islands and tunnels was not the biggest engineering challenge.

The same kind of trench-cut tubes had been used in the Hampton Roads and Downtown tunnels, Fowler said, and a third was under construction at the Midtown Tunnel. So while two underwater crossings meant double the work, the length of the tunnels and the engineering methods used to construct them were already familiar and well-established.

Far less certain was the 12 miles of elevated concrete trestle that made up two-thirds of the crossing.

And when the crews drove the first of what would become more than 2,600 pilings into the unusually hard sand off Chesapeake Beach, the work was slow and difficult.

"When we first started, we were driving the piles from a floating rig — and we were having all sorts of problems," says Craft, who had become Sverdrup & Parcel's resident engineer for the trestles.

"I was worried that we had bitten off more than we could chew."

Even before they began to toil, however, work was well underway in Richmond on a giant $1.5 million machine that would draw international attention as the largest marine pile driver in the world.

Rising from a jumbo barge measuring 70 feet wide, 150 feet long and 1,650 tons, "Big D" could float into place, than brace itself against the waves by lowering four 6-foot-wide, 100-foot-long legs to the bottom.

Its heavy onboard crane could hoist pilings of 200 feet long and more than 150,000 pounds with ease, then place them inside the towering frame of a steam-driven pile driver that not only swiveled back and forth to a exact position and angle but also cut a path for its 25,000-pound hammer with two water jets.

So indispensable did this floating leviathan become that — after it lost a leg, turned over and sank in the fury of the Ash Wednesday storm — work on the long line of pilings came to a halt until it could be partly salvaged and replaced.

"'Big D' saved us," Craft says. "Without it, we'd still be out there."

Monster trio