Field Measurements of Yazoo Clay Reveal Expansive Soil Design Issues

Abstract

Field measurements of foundation movements in central Mississippi have revealed design issues involving expansive soils. At one building, field measurements of the first floor slab at 14 locations show that heaving occurred at a steady rate during part of an extensive drought. The steady rate was maintained throughout the final 21.5 months of a 23.5-month study period following a record drought that occurred at the beginning of the study. The average change in the movement rate was 2.9 mm (0.11 in.) per year over the last 21.5 months. Median movement rates for all the pins varied from 25 mm (0.98 in.) per year to 1.8 mm (0.07 in.) per year excluding the measurements made during the first part of the drought. Elevation surveys at another facility show how the rate of heave is influenced by geologic variations. These surveys also show how the depth of clay (from the surface) influenced heave and how differential movements of a structure are produced from these variations in geology. Design procedures for kind of movement are discussed.