A HARD LOOK AT SOFT ZONES: GEOTECHNICAL SIGNIFICANCE OF EOCENE STRATA BENEATH THE UPPER SOUTHEAST ATLANTIC COASTAL PLAIN
- Soft zones result from early diagenetic carbonate dissolution.
- Soft zones are not cavernous voids, but are isolated, poorly connected three-dimensional features filled with loose, fine-grained sediment.
- In spite of their underconsolidated nature, soft zones have survived through geologic time (tens of thousands of years), withstanding numerous seismic events and maintaining structural competence under significant overburden stresses.
Elsewhere in the region, solution tunnels and small caves have been discovered in equivalent or similar middle Eocene strata. The existence of soft zones and karst features has important land use, construction, and groundwater hydraulic implications. The evidence collected during more than 60 years of soft zone research suggests that, in most scenarios, soft zones and even some karst conditions can be accommodated with adequate geotechnical characterization, conservative engineering calculations, and appropriate design elements.