[tomek_ycomb]

Randomly grabbed some soil strength (it varies alot), but a reasonable number seems 3000 pounds per square foot.

That puts your number at. (3k4010) / (16k*2.2) (estimating width of the 40 foot at 10 feet),

Uhh.. 34 containers. I think that's enough.

In reality you would be able to drive helicoil foundations or any number of things to change the dynamic. I agree the foundations would be secondary to the rest of the system cost in general though