At what level of continuous ground pressure will roots be dammaged.

[Marcus B-T]

Roots can easily exert around 1MPa of pressure so a dry stone wall resting on the ground should be fine. I would be more worried about the long term stability of the wall, but I guess dry stone walls are designed to move about.

[Tony Croft aka hamadryad]

I think theres plenty of trees doing just swell uptight, alongside and through dry stone walls, but I get the facts thing!

 

All this talk of roots and structures, yet we see a sycamore growing 50ft high in a wall crack demolishing the victorian grade egineering bricks and mortar!

[Marcus B-T]

It's quite straight forward realy; all living things grow and adapt in tune with their environment. It is change that is the problem and the more dramatic the change the greater the potential strain on the organism. Anyone who is married with kids will know about that one. If you can adapt though, then you will survive though your morphology or physiology may be greatly changed. Nothing likes having bits chopped off, especially when it is an adaptation to your environment.

[arb culture]

Very well put Marcus.

 

Back to the original question though. There are equations for working out changes in bulk density at depth from a change in surface pressure, but they are very complicated and beyong the ken of most arbs (including me at the moment):

 

http://www.google.co.uk/url?sa=t&source=web&ct=res&cd=4&ved=0CBUQFjAD&url=http%3A%2F%2Fgeo.verruijt.net%2Fsoftware%2FSoilMechBook.pdf&rct=j&q=soil+mechanics&ei=hVOnS8LwDIj40wSL7dTVAQ&usg=AFQjCNGnrxfzeigsS6XIGt7WMLNY-tUn3w

 

Try looking at chapter 40 on page 227.

 

If it's really important you could try asking an architect or a soil engineer.