One of the most persistent errors we see with pavement projects in the Columbia area is treating every subgrade the same—assuming a generic bearing capacity without verifying it. South Carolina's Piedmont region, where Columbia sits at the fall line between the Sandhills and the coastal plain, presents a tricky mix of residual micaceous silts, sandy clays, and weathered granitic saprolite. A pavement section designed on an assumed CBR of 6% that encounters a subgrade with an actual soaked CBR of 2% will rut within the first two seasonal cycles. The CBR road test standard becomes the only reliable way to translate local soil behavior into a pavement thickness that works, not just on paper but through Columbia's humid summers and occasional freeze-thaw mornings. Before committing to asphalt or concrete, we always recommend pairing the CBR with a Proctor test to confirm compaction targets, because density and bearing capacity are inseparable in pavement performance.
A soaked CBR value below 3% in Columbia's micaceous silts typically triggers the need for subgrade stabilization or a thicker aggregate base layer.
