It is a general view that the structure of the multi-component mixtures is complex and possibly intractable with a direct geometrical model (see e.g. Dexter, Tanner (1971)). It is practically impossible to determine empirically a transfer function (e.g. between the grading curves and the dry density) due to the large number of cases. The experimental determination of the “unsaturated soil functions” is time consuming and costly and, these functions are often estimated.