A healthy young tree. Soil is being compacted by excavator used to repair road. Damage to tree may not be seen for a few years. Recommended treatment: break up soil with aeration, high pressure deep root injection with mycorrhizae, liquid fertilizer, pH reducer (citric acid) and micro nutrient pack.
OAK IN STRESS
Clay soils hold onto nutrients. Essential micro nutrients adsorb to clay. Without getting into the chemistry of soil (as much as I want to), nutrients such as (Fe, Mn, Mo,) stick to clay, so the tree is not able to use them. Unless you lower the pH of the soil. Deep root injections of fertilizer with a pH reducer (citric acid) allow trees to absorb essential nutrients. This oak tree will most likely die from lack of nutrients. Treatments would have been recommended when the tree was younger. It still may have a chance with an aggressive treatment of nutrients, pH reducer, and mycorrhizae fungi. However, the cost is much higher than preventative maintenance.