Deodar Cedar
What is the caliper of this tree>?
Sounds like all the uptake roots have been covered, only the structural/ transport roots remain. It is possible that the construction will force the tree to releasse epicormic buds from the roots, starting new feeder roots closer to the tree. Vertical mulching requires and air spade, as does radial trenching. I am not positive what everyone else uses but we use high quality compost sometimes mixed with compost tea and other stimulants.. DO some research about compacted soils and oaks, they are not fond of it. Sounds like if you have enough business the air spade wouldnt be a bad hting to add to your repitoire of services.The spade itself is under 2000, and usually you can charge about 500 per root collar examination/ vertical mulcing etc.. You need a compressor with at least 185 CFM per minute to run it properly, but you can alwas rent them. Another benifit, you can transplant small trees bare root with the air spade by excavating the entire roots system out with it. I even know of one company that transplanted a 40 red maple with it and had tremendous success.