It is a living organism so that makes any assumptions just that. You always run the risk by any disturbance whatsoever. With that in mind there are precautionary measures to take to minimize those risks. Number one that causes mortality to trees during any type of construction phase is compaction. Minimize compaction by not allowing any heavy machinery within ten feet of the drip line of the tree. If you must have the machinery within the perimeter place ten inches of mulch on the drip line to decrease compaction. Second is the health of the tree going into the construction phase, ie... is the tree in a stress phase do to drought, or in a recovery phase from insect or disease. We commonly fertilize trees within the construction zone at least 2 months prior to construction. As far as how much of the root zone can be removed depends on the size and health of the tree. Typically larger trees we dig for resale will lose up to half of their roots during the digging process. obviously the larger the tree the more detrimental this is to the recovery of the tree and the maintenance required after the tree is replanted. If you must dig into the tree roots fertilize the tree prior to the digging. Digging after the tree is dormant will definitely increase survival chances. After digging go around and prune the roots to establish clean cuts. Do not leave root ends exposed to the elements any longer than you have to. Time is of the essence. After root pruning, add good organic topsoil to cover the damaged roots then water in with good root stimulator at least once a month. Do not compact soil you place over roots with machinery. Lastly prune at least 20 percent of the tree above the ground to make up for some of the root loss. Water the tree as needed using root stimulator and just as the leaves are breaking bud fertilize once with good quality fertilizer. Dont forget to continue watering in the heat of the summer. This is when the tree will be the most vulnerable. Also be vigilant for any secondary pest arrising from the trees stress and treat accordingly.