Mark J. Farrow, P.E. 1

It is common knowledge among geotechnical engineers that the Potential Vertical Rise (PVR) of clay soil is a function of clay mineralogy, density and moisture content. Most geotechnical engineers also recognize the potential for large seasonal PVR variations that can occur depending upon the severity of drought and/or wet  weather conditions just prior to the start of construction. However, there are factors other than seasonal moisture variations that affect expansive soil PVR that are not always recognized. The largest variations occur at sites where demolition is required (or has recently been performed) due to pre-existing structures and/or other pre-existing site features. This paper describes various existing site features and their effects on soil PVR variations. It also illustrates the need for an increased number of geotechnical borings at sites where demolition is required or has recently been performed. Finally, the paper presents a quick, simple and economical geotechnical laboratory testing program to identify and evaluate site variations.