2016年09月13日

Typical soil nailed wall

Many citizens have a false sense of security about the soil-nailed wall , believing that the wall was designed to hold back the bluff or to somehow “anchor” the bluff to more stable ground.

The general purpose of the soil nailed wall is to prevent rainwater and surface drainage from washing over the side and eroding the face of the loess bluff. It does not address the seepage of water into the flat surface of the bluff top itself.

The function of the spear-like SOIL NAILS that were sunk into the face of the bluff is to anchor the wall to the side of the bluff. Therefore, it is the bluff that holds up the soil nail wall, not vice versa.

The soil nails in the Natchez Bluff range in length from 20 to 40 to 160 feet.

In a typical soil nailed wall, the average distance between nails (viewed from the top down) is normally 1 nail per five feet.
However, because of the unique and unstable loess soil conditions, the frequency of nails at Clifton Avenue Wall in Natchez (Phase I of the Stabilization Project) was 1 nail per 8 inches when viewed from the top of the wall. (550 soil nails per 450 linear feet). (Source: Innovative Stabilization of Loess Bluff along Mississippi River. D’Appolonia.)

(Click for larger view)
Unlike the diagram above, large sections of the soil-nailed wall at Natchez only cover the top of the 200-ft Bluff. They do not reach the ground. Basically, they hang on the side of the bluff.

The wall does not protect the lower section of the bluff or address the “toe” of the bluff, where mudflow occurs.
It will not stop a problem that originates more than 30 or 40 feet back from the bluff’s edge, which is where most MAJOR collapses originate.
Finally, the Historic Natchez Bluff Stabilization Project was the first time soil nails have been used in the United States in windblown LOESS soils. It is not proven to be a permanent solution.


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