You're right Sean.
The tree roots only have to lift part the weight of the slab over the roots surface area, because they dont lift it off but tilt it. The slabs are just resting on the ground not anchored, be a whole different story if there were screw piers attached. Now if those slabs crack it makes it easier as it means less weight to lift.
In a recent exercise a guy was installing a 20,000L water tank near trees and worried about the weight on the roots. Here's my calculations.
Quote:
Water weighs 1kg/litre, so roughly a 20,000kg or 20 metric tons of weight.
Tree roots need air and having some 20ton weight on them over a large surface area will compact and reduce O2 levels in the soil.
You could pier and beam a foundation for it and not have it on the ground, that means only root interference would be the holes for the piers. Then you just need to address the "no rain" beneath the tank issue somehow.
This one here Tankmasta Water Tanks shows the dia as 3.63m so it would have 10.39m2 surface area. Use this tool to work it out. CIRCLE AREA, SPHERE AREA, SPHERE VOLUME, CYLINDER AREA AND CYLINDER VOLUME CALCULATOR
So you have 1924kg per m2 not including the weight of the tank.
Now if you think about this a bit the average large car weighs that and it's surface area is way smaller on tyres. My calculations show that the above tank would only exert 3psi pressure on the soil but it's the oxygen, water and nutrient factor that would destroy the roots ... not so much the weight. |
So all of a sudden the weight of the water on the tree roots becomes insignificant.
Knowing what roots can exert in PSI before the cells die is the data we require. Like ole Bob says, the tree doesn't want to kill itself so there's going to be a force where cells under pressure no longer function.
Palm roots in retaining walls put side force on the wall and break it, seen that over and over.
Palms between a fence and pool, doubt the roots will push a concrete 40,000L pool so they do damage the other side if there's something there. In situations where there's say a block rendered wall with foundations and a pool and palms planted between in the 1m gap (like a huge pot) what happens? Over time the palms get root bound and start looking like crap, the under plantings look like crap as they get strangled with palm roots and robbed of resources. In effect the whole area becomes like a root bound pot.