Avocado Tree Dying

Clare starts with ...
We are doing major renovations to our home and our avocado tree is not doing well at all. All the grass has gone due to the excavator digging under the house and moving back and forth near the avocado tree. I can see what looks like tiny roots sticking up around the tree which I think are feeder roots but I am not sure. They are now exposed and looking light in colour. The tree over the last couple of weeks has lost it's crop, the leaves started wilting and are now turning brown and falling off. Some of the branches are completely dead but some still have leaves and are green, however I suspect they will also die and fall off soon. We have been watering it every few days as the earth looks really dry. I don't know what else to do to save it or if in fact I am able to save it.

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