A few years back, we were called out to a site near the Hampton Coliseum where a three-story office building had developed serious drywall cracks just 18 months after construction. The original geotech report based foundation design on a single boring with basic classification, but nobody had run Atterberg limits across the full depth of the silty clay stratum. When we sampled at 6 and 10 feet, the liquid limit jumped from 42 to 68 and the plasticity index nearly doubled. That kind of variation is typical of the Yorktown Formation deposits that underlie much of this city, and missing it means differential movement that standard bearing capacity checks will never catch. Hampton sits right where the coastal plain meets the Chesapeake Bay estuary at roughly 37 degrees north latitude, so we get marine clays interfingered with fluvial silts, and the plasticity profile can shift dramatically within a single block. We now insist on Atterberg limits at every major stratum change when working within three miles of the Hampton Roads shoreline.
Plasticity index above 25 in Hampton's Yorktown clays demands we rethink foundation depth, not just bearing capacity.
