The concept of relative moisture in soil mechanics is introduced for assessing the in-situ moisture deficiency and moisture change potential of desiccated expansive clay layers. This paper introduces the terms moisture change potential (MCP), relative moisture (RM), and moisture deficiency (MD) in order to relate the in-situ moisture content to the corresponding equilibrium moisture content at saturation under the same applied pressure. This concept has been developed for sites having variations in moisture content to identify the desiccated zones and to correlate the moisture deficiency to the swelling potential. The paper also defines the saturation coefficient, S-v, as a new term that is numerically equal to the product of void ratio and percent saturation to correlate the initial and final moisture values. Furthermore, it emphasizes that the "relative moisture" term is different from the well-known terms of "degree of saturation" and "relative humidity." The suggested terms are found relevant for assessment of field monitoring records of heave-related movements when evaluating long-term stability of foundations, slabs-on-grade, and pavement as a result of moisture increase and when making recommendations of necessary precautionary measures. In addition, the relative moisture term, defined here, is found to be the more appropriate term to be adopted for soil deposits instead of the relative humidity term commonly borrowed and used. Numerical examples and typical applications are included to illustrate the versatility and validity of the concept introduced. Selected laboratory data of a highly expansive clay are also included. For the application considered, zones of the clay layer showed relative moisture (RM) values of less than 50%, and moisture deficiency (MD) values of more than 100% were classified as highly desiccated. The concept of the relative moisture adopted in this study is concluded to offer a practical means of identifying and evaluating the degree of desiccation of expansive soils for nonuniform sites with varying layer depths and moisture conditions.
