In a pot in my garden I have planted an acorn. It's growing steadily but I know that unless I transfer it to a bigger pot in the future, it will always be confined to that pot. The roots aren't (and never will be) strong enough to break through the pot.
But when I ride my bike along the local cycle tracks in Adelaide I frequently encounter bumps where tree roots have pushed the tarmac up. I've seen the same thing happen where tree roots have grown under roads, and in many cases the roots have managed to push the road surface up and actually break it. The force required to do this must be very high - I certainly couldn't push a road surface up from underneath and break it.
Where is the root getting all the strength from? Surely the division of plant cells isn't strong enough to lift a 2 ton road? It's the same cell division as my acorn is performing in its plant pot?