The excavation could easily have caused the trouble, especially if there was any heavy equipment on the ground near the tree. The symptoms you describe--defoliating early in the fall, few blooms, dead branches, small leaves--are typical of a tree that has endured a severe injury to its root system. I've seen trees in construction zones and flooded sites react the same way. Because they have slow physiology, the damage often doesn't appear until long after the heavy equipment is gone or the floodwaters have receded. Give your tree some TLC to promote recovery. Mulch under the tree, from the trunk to the dripline if you can, to reduce the competition from turf. The best mulches include compost, leaf mold, or shredded leaves because they'll promote soil organisms and healthy soil. The second best mulch would be something like shredded cypress or cedar. Prune off the dead branches but leave every living bit of canopy. During its recovery, the tree will need all of the energy it can produce, and each leaf contributes.