Urban trees are part of our infrastructure. They must co-exist with all the curbs, paving, utilities, and our movements. Various soils and media are available to help address issues like compaction of the growing media, and heaving of paved areas due to tree roots.
I have done projects in the past where we spec’d CU-Structural Soil ® or a similar method to allow great tree growth and thriving amidst lots of built infrastructure demanding structural stability, tight spaces, or other factors. It works.