Study on non-darcian flow sand-clay mixtures

Abstract

Compacted clay liners in landfills can easily develop fissures in a dry environment. To overcome this, sand is added to the clay. In this study, various mixes of sand-clay soils were tested for their hydraulic conductivity, threshold gradient, as well as bound forms of pore water. The water flow behavior in the sand-clay samples varied according to the sand content. When the sand content was no <50%, the compacted sand-clay permeability conformed to Darcy's law. When the sand content was >50%, the permeability deviated from Darcy's law and a threshold gradient became apparent. The lowest hydraulic conductivity was measured in the sand-clay sample with 30% sand content. Based on the seepage theory, the relation between the sand content and the soil's intrinsic permeability was obtained and a model representing the relation between the sand content and hydraulic conductivity was established. Based on analysis of the water morphology between the soil particles, the Hange-Poiseuille law was modified, showing that changing the sand content of the sand-clay can modify the effective apertures of the soil. When the sand content was 30%, the modified effective aperture was the smallest, which explains why the hydraulic conductivity was smallest and the threshold gradient was largest. Considering the empirical relationship between the modified effective aperture and threshold gradient derived in previous studies, this paper furthers our understanding of the development of the threshold gradient in sand-clay soils.