Effects of mica content on hydraulic anisotropy of unsaturated soil

Climate change has affected many aspects of life, including weather-induced landslides around the world. As landslides often cause serious damage, preventive methods such as slope cover systems become more relevant. A good understanding of unsaturated soil mechanics, particularly of hydraulic anisotropy, will be beneficial to the existing cover system. This paper focuses on investigating hydraulic anisotropy, in saturated and unsaturated conditions, of soil having different mica contents. Past research has indicated that the mica content in soil affects its shear strength anisotropy significantly. An initial sand-kaolin mixture without mica was specified and subsequently, coarse mica was added (sand-kaolin mixtures with 9% and 20% mica contents, respectively). Two orientations were tested in this study: horizontal-layering and vertical-layering, obtained by static compaction. Laboratory experiments, including drying Soil-Water Characteristic Curves (SWCCs) and saturated permeability tests were carried out. Specimens with different layering yielded identical SWCCs and had an equalization time ratio similar to the hydraulic anisotropy. The initial sand-kaolin mixture had a unimodal SWCC, whereas the sandkaolin mixtures with 9% and 20% mica contents had bimodal SWCCs. The sand-kaolin mixture with 9% mica content had a slightly higher dry density and a higher hydraulic anisotropy compared to those of the initial sand-kaolin mixture. In addition, the sand-kaolin mixture with 20% mica content was found to have a lower dry density and a lower hydraulic anisotropy compared to those of the initial sand-kaolin mixture. This study concludes that mica content in soil may increase or decrease hydraulic anisotropy of the soil when compared to the initial soil without mica.