Park Service Considers Jefferson Memorial Fixes
Wednesday, May 20, 2009
Almost from the day the Jefferson Memorial opened in 1943, its seawall and north plaza have been shifting atop the layers of unstable river mud on which the memorial is erected.
The 31,000-ton marble and limestone memorial itself appears to be standing firmly on the 11 rings of caissons and piles driven through the muck to the bedrock below.
But the seawall and north plaza, although they, too, are built on piles, have been sinking and sliding at an ever increasing, and alarming, rate away from the memorial and into the Tidal Basin. Cracks appear regularly in the plaza, threatening its structural integrity, and now have to be patched every three or four months.
The National Park Service is now pondering, and inviting public comment on, three major engineering projects designed to fix the problem. All three would take up to two years, and would constitute the most extensive work in decades on one of Washington's most beautiful landmarks.
Here are summaries of each plan.
- Alternative A would be to take no action.
- Alternative B is the park service's preferred approach.
The stones that cover the wall on its top and side would be removed and saved, and the old wall structure would be demolished. Caissons would be drilled like pillars through the mud to the bedrock below and a new wall would be built atop the caissons. To further anchor the wall, steel pipe piles filled with concrete would be drilled through the top of the wall at two different angles. The wall's "capstones" and "facing stones" would then be replaced. The work would hold the seawall and plaza in place, and the plaza would then be repaved to eliminate cracks.
- Alternative C envisions removing the surface of the north plaza. Angled pipe piles would be sunk to bedrock throughout the plaza. The plaza would be repaved. The seawall's facing and cap stones would be removed and saved. "Micropiles," made of one or more steel bars, would be drilled at two angles through the existing seawall, and the seawall stones would then be replaced.
- Alternative D is the most radical option. The plaza surface would be removed, and most of the soil underneath would be excavated and trucked away. It would be replaced with a "more binding" soil. The plaza would then be repaved. The seawall would be reinforced with micropiles, as in alernative C.
The public can read and comment on the repair plans at http:/