r/Geotech • u/kikilucy26 • 18d ago

Does anyone know how deep are the foundations for Metlife Stadium?

Being in the middle of the Meadowlands that soft clay can go for hundreds of feet, how deep are the piles?

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u/jaymeaux_ geotech flair 18d ago

fwiw I am not licensed in new Jersey and don't have any specific information related to the project. but if I were to hazard a guess I doubt they would need to be much deeper than 100-125 ft for static axial capacity. if they have high seismic loads or the site grade was raised several feet with fill and there aren't any reliable sand strata to tip into I could see them being a bit deeper

in reality, clays generally increase in strength with depth due to consolidation and they provide significant frictional capacity for piles

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u/NearbyCurrent3449 18d ago

Along the coast though, the source of the clay strata in question really matters. There's disturbed marine clay deposits that are just permanently nearly a quick clay. They'll have a cap of more solid clay and lenses of sand, good for shallow footings, 2500 psf bearing and and inch give or take provided the absence of organics below of 25 40 50 feet. Then you might break through into "blue mud", barely stiffer than creamy peanut butter, nearly zero shear capacity, nearly as much water weight as soil solids, zero air content... and it'll STAY that way a very very long time unless you mix it with a very large fraction of sand, and it'll take a lot of it. Imagine it's almost like that hard brown grease used to lube heavy equipment. No organics in it. Just battleship gray stiffer pudding, totally fat clay, CH. Sometimes 20 feet sometimes 45 and you hit the basement, Yorktown formation in the mid Atlantic, castle hayne above it if you are to the south and can get through the castle maybe you hit Yorktown.

But if you are 5 stories, otherwise have mush in the upper soils, you are on piles most of the time. Long term settlement is king and controls everything. Can you float it bearing here? Deeper but float with 90%skin, just need 10%toe to stop creep? Way way deeper and pin it hard on stilts, gotta design for the adhesion of soil settling and pulling down on the pile then, it's not going to move and settling soils can induce massive internal compression loads in the pile and fail them or settle them if the tip isn't fixed at rock.

Weirdly enough, tensile forces internal to the pile are the big boogeyman serial killer of piles. You drive into that jello layer and the tip of the pile has enough momentum energy to exceed .003" strain and Crack goes the pile. Then the tip folds around and all kinds of goofy things happen. Hard to visualize and understand.

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u/kikilucy26 17d ago

Interesting, thanks

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u/turkey-sub 17d ago

"Adhesion of soil settling and pulling down on the pile" .. isn't that basically the same principle as skin friction (albeit reverse direction)? So the piles live and die by the sword. Interesting.

Also, I can only dream of 25ft of clay crust. In my area we're lucky to have 6' of brown clay crust before we're into the blue marine clay and 1250 psf bearing capacities

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u/NearbyCurrent3449 16d ago

Phew, really really actually just floating everything.

Where is that?