I think that this is a question for civil engineers and estimators only. But the answers, if they come, will be well worth the rest of us thinking about.
In conjunction with hi-rise apartments, Amacon is also including 2-level underground parkades. Where they go, and whether they'll all be connected or not, is unclear.
The question “How much?” is very tricky, because there exists under the mall (under most of St.Albert, for that matter) starting only (roughly) half a meter below the surface, and (roughly) 30 metres deep, Lake Edmonton gumbo. IE, highly plastic clay that swells and shrinks with humidity variations.
So not only are there the normal parkade construction challenges (expansion joints, joint waterproofing, and damp-proofing). On that site, the plastic clay will need to be kept at a constant humidity level, and the parkade perimeter will require constant, unfailing de-watering. Failing which, unless heroic measures have been taken, very nasty things will likely happen. The wall joints will fail, and the lower floor slab will heave. And then comes flooding.
Heroic measures may well demand piles, not only to prevent the sinking of any part of the parkade, but also resist uplift caused by swelling of the clay when/if its humidity level rises.
I know enough about the business to utter predictions. But I have no idea what heroic measures will need including, nor the current cost.
The question then is: what will be the total of land cost, construction cost (let's say those two distributed over 300 months, plus all operating costs … per month?
And so, including for profit and indirect overheads, how much rent will have to be asked per standard-sized car , with one stall per 40 square metres of gross floor area?
I'm only wildly guessing: quite a bit over $150 monthly, with strong resistance somewhere between $200 & $250.
Yet a parkade of say 2000 square metres will accept only 50 cars. @$150/month, that's only $7,500.
Enough to pay the (5%) interest only on a loan of $1,800,000. I dunno, that feels light to me.