Soil Moisture Deficit Analysis

Abstract

In the explanation of shrinkage phenomena in soils, use of the soil moisture deficit concept has proved to be a valuable method. The ratio between soil moisture deficit and vertical shrinkage is known as the water shrinkage factor. If both of these values are known for a soil, the associated shrinkage can be determined. Data from a recent case history were used in a parametric evaluation of the soil moisture deficit calculation. Moisture content profiles and their relationship to the moisture deficit were examined. This study includes a brief review of the field capacity concept from the soil science discipline and how it relates to soil moisture deficit and shows instead the relationship between the ending equilibrium moisture content normally used in unsaturated soil mechanics and the soil moisture deficit. The equilibrium moisture content is related to low matric suctions. Because of the occurrence of persistent soil moisture deficits, it is difficult to arrive at seasonal changes in moisture content profile on the wet side. This study predicted the moisture content profiles equivalent to the ending equilibrium moisture content and concludes by presenting an example of the calculations of the cumulative soil moisture deficit and cumulative soil shrinkage. A comparison of cumulative soil moisture deficit and shrinkage between two control profiles in the example ranged from 63.0 to 83.5 mm and from 16.1 to 21 mm, respectively.