Digging up tree roots when re-paving driveway

I have a large, mature silver maple that's planted about 2 feet away from my driveway. I am currently getting estimates for getting my driveway (40 years old) re-paved. In the scope of work, the contractors say that they will excavate 12" of the old driveway, put in a 10" gravel bed, and 2" of asphalt. I am concerned as to how much root damage my silver maple can sustain.
Below is a very crude "overhead" picture of the current driveway and tree. The trunk of the tree is represented by the letter "O". As you can imagine, any roots of the tree 12" deep from roughly 1 o'clock to 5 o'clock will get severed. Is that too much damage? It is a large silver maple. The diameter of the tree's trunk is probably at least 3 feet, and its crown could easily be 45 feet wide.
|....| |....| |....| |....| O |....| |....| |....|
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On 29 May 2006 06:45:47 -0700, jonny snipped-for-privacy@hotmail.com wrote:

That's pretty severe damage. The percentage of root loss is harsh, but not necessarily unforgiveable. But severing roots that close to such a large tree will mean losing most of its anchoring abilities on that side--i.e., don't put any picnic tables on the side away from the driveway.
A tree's roots exist primarily in the top 12" to 24" of soil. Depending on your soil and the site history, you could be losing virtually all of the roots on this side of the tree. There are alternative contruction methods that would either replace the concrete slab with porous paving materials or elevate the drive above the root zone (or perhaps you could reroute the drive a bit to give this tree some breathing room--even a few extra feet would be better than nothing).
If you decide to continue the project as it's planned and still keep the tree, be acutely aware of protecting what you can. If the work crew gets careless while replacing the drive, branches could be broken or the remaining soil could be compacted, thus leading to even more root loss. Write penalties into your contract for any damage to branches or bark on the aboveground part of the tree. http://www.treesaregood.com/treecare/avoiding_construction.aspx is a good source to learn how to protect your tree during construction (and includes a link to other tree info, including remediation of the damage that does occur). Along with the info it contains, I would emphasize the value of mulching the root zone heavily where possible to help avoid compaction where the driveway isn't.
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