Below The Beltway

That’s the concern that’s being raised by this report in The Washington Post:

Up on the surface, the signs of the trouble at the Jefferson Memorial are small:

A few blacktop patches over uneven seams in some concrete. A cordoned-off section where the sea wall has slipped below the front plaza. The “tilt meter” boxes that visitors can’t see unless they know where to look.

Underground, though, the problems may be huge: Slowly, almost imperceptibly, parts of the complex seem to be sinking into the mud.

It’s probably not endangering the majestic 32,000-ton domed structure itself, although it’s being monitored for movement.

The big problem seems to be a section of the sea wall that is breaking from the memorial’s plaza and settling into the Tidal Basin. The “ring road” along the memorial’s circumference also seems to be shifting, officials say.

Such movement is an alarming — and chronic — problem at the Jefferson Memorial, which was built in the late 1930s and early 1940s atop pilings and caissons sunk into an artificial mud flat that is about 100 feet deep. Engineers have been struggling for decades to keep everything firmed up.

The National Park Service, which oversees the 18-acre memorial site, is trying to see how bad the movement is this time and is wondering what it will take to fix it.
The current problems, at one of the most photogenic monuments in the country, were noticed early last year, said Stephen Lorenzetti, acting superintendent of the National Mall & Memorial Parks.

Since then, the western section of the sea wall, which separates the memorial complex from the Tidal Basin, has dropped in places about six inches below the plaza, which it adjoins.

And the ring road, which wraps around the memorial, has also slipped several inches in spots. It is patched where it meets the plaza.

Since the Jefferson Memorial, like much of Washington, was built on top of what used to be swamp land, this isn’t entirely surprising:

The memorial was built on six inner rings and five outer rings of caissons and piles driven through the mud to bedrock far below, according to engineering reports and news accounts. At least one support was sunk 138 feet to bedrock, according to the Park Service.

The nearby Lincoln Memorial, Franklin D. Roosevelt Memorial and Korean War Veterans Memorial also are built on pilings atop fill. The Lincoln Memorial’s pilings go down about 40 feet; the FDR Memorial’s, 80 feet; and the Korean memorial’s, 30 to 60 feet. There have been no settlement problems with those memorials, a park spokesman said.

At the Jefferson Memorial, periodic settlement has been an issue since before the structure was dedicated, according to the accounts.

As early as 1941, some of the supports under the memorial’s main steps began shifting and had to be temporarily lashed together with steel cable and turnbuckles, according to an engineering report done for the Park Service in 1965. Settlement also caused other supports under the steps to bend slightly, the report says. And the steps moved so often that park rangers once kept a special tool at the site to realign them, the report says.

At present, the Memorial itself does not seem to be in danger. Hopefully, it will stay that way.