Saturday, June 16, 2007

The Sinking of the Jefferson Memorial

The Washington Post reports today that the Jefferson Memorial is having problems with stability because the land around the memorial is sinking.

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.


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.


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 core issue is that the monument is built on top of fill that was dredged from the Potomac River during a project to deepen a shipping channel. While the engineers took steps to ensure stability, such as driving pilings to the bedrock, the site has had problems with subsidence from the beginning. I have noticed this problem myself during my occasion walks along the Tidal Basin and Hains Point. At several points, the sidewalk takes a funny angle, does not align with the seawall, or appears to have little supporting it underneath. I am glad to see that NPS engineers are on the case.