Site classification of an excavated area
Site classification of an excavated area
(OP)
I am working on a foundation design for a property that has been excavated 25m below the ground surface. Would the site classification for seismic design be based on the soil properties from the ground surface or the soil properties from the foundation elevation (25m below ground)?





RE: Site classification of an excavated area
RE: Site classification of an excavated area
RE: Site classification of an excavated area
RE: Site classification of an excavated area
We you say "a property excavated to 25 m below ground surface", I get the impression that you are referring to a property much larger than the planned structure. In this case, the site seismic classification is based on the current ground surface (assuming no basement) which is 25 m lower than previous ground surface. If the footprint of the excavated area is small (relative of the 25 m depth of excavation), you are in a complicate situation which require detail analyses.
RE: Site classification of an excavated area
RE: Site classification of an excavated area
RE: Site classification of an excavated area
RE: Site classification of an excavated area
I believe geo77's original post raised the question of shallow foundations cast upon the bottom of a deep excavation.
That would not be the same case as of deep foundations.
I also believe that many regulations take as a reference level for deep foundations (on piles, on slurry walls, on caissons) the foundations head near ground surface.
And I fully agree on the fact that with tall basement walls we might be in a more complex area requiring in depth analysis; site classification based on the deep level might be under conservative, whereas if referred to the ground surface it may be over conservative.
In major works with huge amounts of concrete involved I reckon design optimization may allow to save substantial amounts of money.
In some building regulations (like the Italian ones) unfortunately there are no suggetions for such a case.