BSmith:

A backhoe would be the best solution to a real hardpan. Your method might help and then again the roots might find their way through without help. It depends on the nature of the hardpan.

Is your hardpan something that is brittle and really does fracture like rock? Or is it more like an impermeable clay? Does the water pond above the hardpan or is drainage of the topsoil good? What color is the hardpan and subsoil?

Yeah but a backhoe on a quarter acre would take up to much space in the driveway. HA! If this was a large operation tile drainage would be the way to go.

The hardpan here is an impermeable clay mixed with rocks the size of penny to the size of two basketballs very tightly packed. Therefore in heavy rains >4" the topsoil saturates and water slides along the hardpan like a water slide following the contours of the land.

Hardpan is a brown color due to the clay content. Similar to this picture from someone on the web http://firesafegarden.com/wpblog1/wp-content/uploads/2012/02/gardensoil2012-1024x768.jpg but so tightly packed you can't dig through it with a shovel due to the rocks. The subsoil is a light brown and consists more of sandy loam.

Brown is better than gray. Gray indicates soil that is constantly wet. The roots may penetrate the clay layer on their own. So I don't know if a few small holes poked thru the clay will help any. Mixing with a backhoe would likely help tree vigor a great deal. But too much tree vigor can be bad for fruit eating quality.