Help with Apple Tree

Hi All,
We are replacing our deck and have to excavate around an Apple Tree which we think is a Cox's Orange Pippin. When we moved in the tree was in a sorry state with borer and rotting branches. 2 years ago we gave it some vigorous pruning and fungus/ insecticide and last season it produced 8-10 shopping bags of perfect delicious apples.
The Apple Tree is about 14cm's in diameter and about 12feet tall maximum. There's not many branches as lot got pruned out because of rot, we don't know how old this tree is.
I need to excavate to a depth of 25cm's either side of the tree about 60cm in width. The excavation will start about 1 metre away from the trunk either side of the tree and move away from the tree.
Can the Apple Tree survive this cut. I will definitely hit some roots and will need to cut through. It is flowering now and summer is around the corner.
Please help.
I will go outside nowto continue digging/ building so please leave your advice. Thank you in advance. I shall be back later to check for replies.
Cheers, G

You have not given a vital piece of info ,the soil type there.If the soil is friable (loose) and free draining the tree will be fine
.You are in fact doing a drastic version of what commercial growers(me) call root pruning.This stresses the tree to set more fruit and to produce more flowering (fruitful) buds for next year.You will need to ensure water gets to the lower roots afterwards .Can you get 2 lengths of 25mm galv pipe about 1-1.2 mt long and drill 6 -8 holes across one end 30 mm apart (one above the other.)then drive these in about 600-700cm on either side of the tree with a wooden mallet or wood cap.You can then connect a hose to these at low pressure and water the lower roots twice a week for an hour at least.
Also you will need to brace the tree well as it will loose a lot of stability
and any wind movement will damage the remaining roots badly.
Finally, paint the trunk with a mixture of phosphoric acid (phosguard or phoschek)and summer oil (50/50) 3-4 times over summer to prevent root rot (phytophthora).
If the soil is heavy clay or rocky (causing shallow rooting) you may not be able to save the tree after removing that much root material .
In that case you should invest in another good early variety like Premier Star .Check out the web site www.premierstarapple.com for details.

Any further questions !

THAT ^ ^ ^ & do it ONE side at a time with as long a time span as possible.between cuts