Jefferson Memorial's Signs of Sinking Raise Fresh Alarms

PHOTOS
Sinking Stones
Although the Jefferson Memorial itself appears stable, parts of the complex around it seem to be sinking into the mud of the Tidal Basin.

Park officials are also concerned about the flooding that for the past few years has inundated parts of the southern rim of the Tidal Basin just west of the memorial at high tide. The water covers sidewalks and landscaping and forces the park to close walkways and post signs about the high tides.

The cause of the flooding is not clear, but the shore of the basin is also made of fill. "It used to be river," Lorenzetti said. "So that is another point they're looking at -- to see if the land itself is sinking."

In addition to the two tilt meters attached to the stones of the sea wall, engineers have installed inclinometers to help detect movement and other devices that measure soil pressure beneath the monument, said Rabih Khouri, a Schnabel engineer who was working at the site last month. Core samples of the earth have also been taken, he said.

Most of the area, in what is now West Potomac Park, was created about a century ago with mud dredged from the Potomac River shipping channel. The memorial's site, once a racially segregated Tidal Basin beach, was selected in part because it is on a direct north-south line with the White House. Other locations considered were near L'Enfant Plaza and what is now RFK Stadium.

Dedicated in 1943, the marble and limestone memorial was originally supposed to be in the middle of the Tidal Basin. In the end, it was built along the south shore of the basin, and a man-made promontory was added to the man-made shoreline to accommodate construction.

It was not the best foundation for a huge stone memorial.

"Rome was built upon hills," a reader wrote to The Washington Post in 1938 after site preparation had begun. "Why do we in Washington ignore history and good judgment and select the swamps or lowest places we can find on which to erect some of our gems of architecture and engineering?"

The builders realized there would be a "settlement continuum," said Perry Wheelock, the Park Service's chief of resource management for the National Mall & Memorial Parks. "They constructed to accommodate it as best as they were able," she said.

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.

Lesser settlement problems continued to crop up around the memorial during the 1940s and '50s.

By the 1960s, the plaza, which was not supported by pilings, began to sink -- by as much as three feet, according to a later Park Service review. And a $1.1 million engineering project -- $6 million in today's dollars -- was undertaken from October 1969 to December 1970 to bolster the area with pilings and other supports.

Through all this, the sea wall along the memorial's northern rim appeared sound. Unlike the plaza, the sea wall was supported in its original construction by timber pilings -- especially "batter" piles, which are set at an angle to provide more support.

Wheelock, of the Park Service, said it is a good possibility that the timber piles "are approaching the end of their usefulness."

The ring road has never been supported by pilings, Lorenzetti said.

He said that once the park gets the engineering report, it will seek funding to make the repairs.

"The idea first would be to repair the sea wall right in front of the plaza, and then work our way out from there," he said, "out along the Tidal Basin and on to the ring road, assuming that's where the problem lies."