Soil-water characteristic curves and dual porosity of sand-diatomaceous earth mixtures

The soil-water characteristic curves (SWCCs) for sand-pelletized diatomaceous earth mixtures are measured. The measured SWCCs are bimodal due to two distinct pore-size distributions associated with the microscopic (intrapellet) and macroscopic (interpellet) porosity regions of the pelletized diatomaceous earth. The measured data for the bimodal SWCCs are fit with modified forms of the Brooks-Corey, van Genuchten, and Fredlund-Xing SWCC functions, and the microscopic and macroscopic porosity portions of the mixtures are determined from the SWCC fits. Both the total and the microscopic porosity of the mixtures increase with increased percentage by dry weight of diatomaceous earth in the mixtures. However, the macroscopic porosity of the mixtures is essentially independent of the diatomaceous earth content due to the similarity in the particle-size distributions of the sand and the diatomaceous earth. The results suggest that sand-diatomaceous earth mixtures may be useful in applications where an increase in water-holding capacity (that is, relative to sand) is desired, such as in landfill covers. In such applications, a balance between the increase in cost and the increase in water-holding capacity due to the use of the diatomaceous earth must be achieved.