I have a Twisted Acacia tree, about 12' tall, that is starting to uproot. Because the plant is actually a shrub that can be pruned into a tree shape, perhaps it is top-heavy, but my suspicion is that the roots haven't penetrated the soil downward enough. (I am in the desert but also in a river valley and the soil is clay heavy.) Is there a way to penetrate the soil and loosen it / add gravel to encourage the roots to go downward?
Probably root-bound, from having been left in a pot too long at some point. This is very common in this age of container production of nursery stock. If that is the case with your tree, all you can do is install a firm stake or pole, attach it to that.
They are not that long lived either as a rule 10-15 ys . I have just had very mature black wattle trees (25+ yrs) turn their toes up because of dry weather and age. They were in good soil. Liz
Black wattles ( Acacia mearnsii) http://asgap.org.au/APOL19/sep00-4.html normally do the "toe turning" at a fairly young age. Mine were good specimens and already large when I came here 25+ yrs ago so they have had a good innings. The drought has also killed my beautiful blackwood (Acacia melanoxylon) http://www.anbg.gov.au/acacia/species/A-melanoxylon.html which was a very fine specimen. All the ones down on the main road have had to be removed as they were crashing down all over the place. Hopefully with the fair bit of rain there will be a lot of regeneration. Our road edges here are still natural bush and in my case this extends into the bottom paddock. Re expression fairly common here. I thought it was one of yours from whence we source a few. :) Liz