how much pressure would the roots of a tree apply to crack a 4in. cast iron sewage pipe?

Question

instead of a pipe make it a sidewalk

Answer 1

It needs to apply surprisingly little pressure. The roots get into small openings and then increase in diameter, putting pressure on a small hole in the cast iron. That puts the cast iron into tension to push the opening wider. Cast iron is very strong in compression but much poorer in tension.

For example a piece of cast iron with 80 kpsi compression strength has only about 20 kpsi tension strength.

Answer 2

I believe that weather extremes might be more to blame. The weather might have been the trigger that caused the pressure to crack the pipe. Normally, in tropical countries, the roots would push away the dirt or porous cement. I built a vacation home in the Caribbean and the tap root of a Neem tree has actually moved my back step away from the house

Boaz.

Answer 3

That would depend entirely on the thickness of the pipe wall.