Florida Clay Gets a Bad Rap

In many areas of the United States clay soil is the major building material available for construction of foundations. However, in Florida, clay soils are shunned; they are either removed or covered by substantial thicknesses of granular material. Although only a small percentage of clay occurring in Florida is known to be expansive, this onerous quality has influenced many to label all clay expansive. In many sinkhole investigations when clay is found near the foundation, it is summarily decided that the clay is expansive and is declared the cause of building distress. This paper is intended to remove some of the myths surrounding Florida clay and provides practical methods for indentifying expansive clay. It also includes a review of clay testing methods and provides suggestions for efficient methods of testing for expansive clay. The discussions are directed to the occurrence of clay, particularly in sinkhole investigations, and the likelihood of its occurrence causing building distress.