You do have to remember, total weight doesn't matter as much as weight per square foot. So the cage size doesn't matter, it's more dependent on how deep the layer of dirt is.
For instance, you could have a 20 foot long, 20 foot wide cage, and if you put in six inches of substrate, it would weigh about 13 tons in total.
But if you had a 4 foot by 2 foot enclosure, and put in two feet of substrate, it may only weigh one ton, but it would be more focused on one spot. So even though it would weigh less in total, it would actually be more likely to fall through the floor.