"Tim May" wrote in message ...
In article . com,
wrote:


Piles don't have to reach "bedrock" to work. Friction can hold them
in place.
Just spotted something.

Both New Orleans & Lake Pontchartrain are on the Mississippi delta,
with Lake Pontchartrain being on the North side of New Orleans.
Sediment under Lake Pontchartrain is reportedly 20,000 feet
deep .... the bedrock is under that, as the oil drillers know.
I don't recall any mountain-building processes in the area that
would have created a 20,000 foot tall mountain under the site of
New Orleans.
So I'd guess that your 80 foot number just applies to how deep
pilings are driven for some purposes and has nothing to do with
your assumed bedrock depth.



You need an education, boy.

Building foundations need only be sunk to the point where a building is
floating.


--Tim May

http://www.southbear.com/New_Orleans/Geography.html
[
When the French arrived at the end of the 17th century, they were greeted by
this swampy land that they called Le Flottant (the Floating Land). Their description
was not far from the truth. The land is naturally very wet, even spongy. A person
must dig through twenty feet of land through a hole that would quickly drown him
as it filled up with water before he reached what can be loosely termed "solid ground".

He'd have to dig another 80 feet before he reached bedrock consisting of compacted
clay, and silty sand. For this reason all structures of any significance must be built
on pilings hammered deep into the ground. Skyscrapers are a new feature to the
city's landscape, as these require pilings of thick concrete set more than a hundred feet
into the ground. Such is the nature of a low-lying alluvial plain such as the Mississippi
River delta.

Surrounding this Floating Land on all sides is water, lots and lots of water. The French
saw the land as an island, which they named the Isle d'Orleans (Isle of Orleans). The
Isle d'Orleans soon became a political and regional entity with geographic boundaries.

These boundaries (outlined in yellow on the photo-map at left) were identified by the
French as the Mississippi River on the west and south, Lake Pontchartrain and Lake
Maurepas on the north, Breton Sound (part of the Gulf of Mexico) on the east, and
what the French named the Iberville River (that connected the Mississippi at Baton Rouge
to Lakes Maurepas and Pontchartrain) to the northwest. This area is on the east bank
of the Mississippi River. However, throughout Louisiana's history - after the territory
was divided along the river itself, and only that part of the original territory west of
the river was known as Louisiana - the Isle of Orleans remained a part of the Lousiana Territory.
]