According to the PBS documentary, the slurry wall
was in danger of collapse and needed to be stabilized. The claim here is the facade damaged the floors. Now, how valid is this claim? Did the facade damage *all* of the floors? Is he talking about the basement floors, directly underneath the towers, so the facade fell inward? (Note the slurry wall is 80 feet deep, and there were 6 or so floors below ground, or part of the basement.) In another description, a geotechnical engineer says the collapse of the basement slabs was the reason the slurry wall was destabilized. This seems an interesting difference - Tamaro is careful (or maybe not?) to explain that the facade blew away the floors, Ling simply states the basement collapsed. (Also note the engineer's complaint about not having soil tests. This is mentioned because some will mention that because no one complains about not having valid information and evidence, whether engineering plans, steel samples, soil samples, etc, then it must not be an issue and does not stand in the way of making conclusions. Here it seems clear, that the engineer may not work for NIST, but is expressing that the lack of data is an issue).

Libeskind seems not to understand exactly what happened either, as he waxes eloguently, about the slurry wall and the foundation, likening it's durability to the Constitution and democracy but he seems to misunderstand that the slurry wall *had* partially given way _because_ the foundation had collapsed. But that would take away from the drama of his prose perhaps... ;)

From my understanding, the basement area encompassed a much larger area than just the two towers, it included WTC 3,4,5 and 6. I think what is probably meant by 'facade' would be the steel perimeter columns. These obviously fell outwards and would be what did a large amount of damage at the perimeter of the site.

There's a nice image somewhere showing how large the basements actually were but I'm afraid I don't have it to hand.

The wall would be laterally supported at each floor by the slabs. This is a fairly standard way of doing things. The wall itself would likely be engineered to be as cheap as possible, which means that it can only span between one floor without failing. Soil failure is pretty slow though, which is why they knew in advance.

You can see how the floor slabs are keyed into the wall here: http://www.civil.columbia.edu/%7Eling/wtc/ce4a.jpg

A Geotech report on the soil would be useful, but it's really not necessary. The collapse of that wall is pretty straightforward

I think the geotech guy explained pretty well why a soil sample would be useful, if you read the link. It's possible Tamaro took one, and didn't release the data - fairly typical in this entire systems failure.

As far as the slurry wall failure, that's certainly straightforward. The collapse of the supporting basement floors is an entirely different story however. Tamaro's theory is the steel facade somehow did it, but he seems on shaky ground.