approach for estimating the shrinkage geometry factor at a moisture content

Soil shrinkage is characterized, along with the shrinkage curve, by a partition of the volume change of the soil matrix between contributions of cracks and soil subsidence. This partition is determined by the shrinkage geometry factor (r(s)). Knowledge of the value of r(s) is important for the consideration of water and solute transport in swelling and cracking soils. The r(s) concept was recently used for the generalization of flow equations in the case of the axially symmetric two-dimensional deformation of shrink-swell soils. Sufficient accuracy of the r(s) value is very essential for all these applications. However, the theoretical definition and available measurement method of the r(s) factor include some implicit assumptions that are disturbed in real conditions. These disturbances, which are not accounted for in r(s) measurements, can lead to distortion of the r(s) value. The objectives of the work are: to explicitly formulate the assumptions; to introduce a new presentation of the r(s) concept based on a comparison between different shrinkage curves of a soil; to suggest an approach for estimating the r(s) values corrected by taking into account the disturbance of one of the assumptions; and to experimentally illustrate the approach using the simplest case of pure-clay paste samples when they dry, shrink, and crack. The results show the necessity and practical possibility of considering the r(s) factor as a function of soil moisture and introducing to the factor the multiplicative correction that is connected with accounting for possible macrocracks in soil samples to be used for experimental estimation of the r(s) factor.