Can I repair 3 #2 Aluminum wires going from the main breaker box (200 amp) feeding a 100 amp sub panel 50 feet away in a garage shop. We accidentally broke all 3 lines while digging up a tree. Can it be patched and re buried?
It was not as deep as it should be.

You would need to cut back well into good wire. Do not splice it right where it broke. The cable is most likely stressed and contaminated within a couple of feet of the break.

You'll obviously need six direct bury splices and heat shrinks, and enough wire to make up the difference.

If the Problem is close to one end, Maybe pull new wires on the short end and have 1 set of connectors.

If this is a direct feed from your main panelboard to a downstream panelboard, you MUST have a four wire feed!

Also, within the downstream panelboard, Ground and Neutral must be isolated from each other.

If this is a direct feed from your main panelboard to a downstream panelboard, you MUST have a four wire feed!An older feed to a detached structure could very well be 3-wire and be perfectly legal. In those cases the grounds and neutral are bonded just as they are in a main panel.

I agree, but if the cable is severed as described above, and replaced. Wouldn't need to be replaced with a new 4 wire cable?

IMO no. It is just a repair.