Toronto Sugar Wharf Condominiums (Phase 2) | 283.6m | 85s | Menkes | a—A

Drilling equipment onsite


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I remember reading once that the weight of the earth removed is roughly the weight of the skyscraper that is built on top of it so the two basically cancel each other out. True?
Nope. If you excavated to a P3 level (for example) and built a 10 storey building, that's going to weigh significantly less than excavating to a P3 and building a 40 storey building (or 50 or 80 etc.).
 
Also to add, there are cases where cities/areas are literally sinking partially due to the sheer amount of pressure their buildings place on the earth below. New York is a famous case of that:

 
I remember reading once that the weight of the earth removed is roughly the weight of the skyscraper that is built on top of it so the two basically cancel each other out. True?
"For every action there is an equal and opposite reaction"
I think you're thinking of buoyancy calculations, the weight of water displaced equals the weight of the boat.

Building's don't need to consider this kind of action; the only reason we dig down is to provide substructure floor area for things like parking, foundations, and elevator pits. It would actually be substantially easier to build if you didn't require underground parking - you could avoid most of the water ingress and lateral earth pressures, and save a ton of embodied carbon by not pouring so much concrete.

Also to add, there are cases where cities/areas are literally sinking partially due to the sheer amount of pressure their buildings place on the earth below. New York is a famous case of that:

Mexico City is probably a better example, but this has to do with soil quality. The buildings would likely sink regardless of "how much soil is removed" from the excavation, so long as their foundations are inadequate for the "soil" they rest on.
 
...I guess they had a lot a of weird things sitting in LCBO storage and what not if leaked into the ground could cause future residents to sprout new limbs or organs. So gotta take care of that first!
 

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