Book excerpt: The scope of this research includes the development of criteria to define the need for undercutting, the depth of the undercut, and the quality of the backfill material such that the cost and performance are optimized. In addition, chemical stabilization ahd geosynthetics reinforcement, in combination with several thicknesses of the ABC were studied to provide comparative criteria for the enhancement of various poor subgrade soils encountered in N.C. with, or in lieu of, undercut and replacement with select fill. The criteria are presented along with the associated relative costs of each alternative.