Can a decades-old michelia alba w/ root loss (minimal, we excavated the backyard 5 ft around it) be saved?How?

Question:Michelia alba campana. We finished our backyard excavation (careful to leave 5 ft around the tree trunk) one week ago. In that time, the tree has lost nearly all of its leaves. The tree is about 20+ feet high. The fallen leaves are a mix of brown, yellow and yellow with brown spots. We haven't seen it this bald in the 1 year we've had the house. We did notice that about 3 roots with a diameter of 2-3 inches were cut off in the excavation process. Not sure if this was the reason as I've read that root disturbance is tough on this tree. Or could it be that there was extra dirt (about 1-1.5 feet) piled around the trunk?

Is there anything we can do? We love the tree and were trying to excavate and plan landscaping around it...any help would be appreciated. Thanks!

Answers:
remove extra dirt on roots, add mulch and water heavily. now would be a good time to prune it back