NONUNIFORM VOLUME AND WATER-CONTENT CHANGES IN SWELLING CLAY SOIL .1.THEORETICAL-ANALYSIS

In many clay soils, drying and wetting cause non-uniform changes in wa ter content and in the volume of soil and peds. Theoretical relations between total volume of soil, soil thickness acid water content are so ught for non-uniformly swelling and shrinking soil. Such soil is assum ed to be composed of small elemental volumes, each of which does swell or shrink uniformly. It is also assumed that the non-uniformity of sw elling or shrinking in such soils arises solely from spatial variation brought about by variations in evapotranspiration and infiltration. A constant ratio between movement of the soil in the vertical and horiz ontal dimensions is assumed for all elements of soil, By averaging ove r the soil volume the equations describing the volume change of indivi dual elemental volumes, the averaged equations for non-uniform volume changes may be obtained. They show that the average and the spatial di stribution of the changes in soil thickness determine the average chan ges in water content of the soil. It is concluded that the equations f or uniform and non-uniform volume changing soils, though formally diff erent, should in practice produce nearly identical results for clay so ils.