RELATION BETWEEN VERTICAL SOIL MOVEMENTS AND WATER-CONTENT CHANGES IN CRACKING CLAYS

Field studies on swelling and shrinkage in clay soils are scarce, due to the lack of sound experimental methods and suitable mathematical equations. This study was aimed at developing such methods and equations. Disks were positioned at various depths in the soil in order to measure vertical movements in undisturbed soil. Newly developed equations were applied to convert these vertical soil movements into three-dimensional volume changes and crack volume and to relate them to water-content changes. These equations are unique in that they are valid for water loss in the structural-, normal-, residual-, and zero-shrinkage phases, and for both isotropic and anisotropic shrinkage. Methods and equations were successfully tested in a 1-yr field experiment in a heavy marine clay soil in the Netherlands. The use of seven rotating disks for measuring soil volume changes was about 10% more accurate than two other less laborious methods. An interesting application of this method and equations is the determination of soil water-content changes by measuring vertical soil movements.