Impact of mica on geotechnical behavior of weathered granitic soil using macro and micro investigations

The micaceous weathered granitic soil (WGS) is frequently encountered in civil engineering worldwide, unfortunately little information is available regarding how mica affects the physico-mechanical behaviors of WGS. This study prepares reconstituted WGS with different mica contents by removing natural mica in the WGS, and then mixes it with commercial mica powders. The geotechnical behavior as well as the microstructures of the mixtures are characterized. The addition of mica enables the physical indices of WGS to be specific combinations of coarser gradation and high permeability but high Atterberg limits. However, high mica content in WGS was found to be associated with undesirable mechanical properties, including increased compressibility, disintegration, and swelling potential, as well as poor compactability and low effective frictional angle. Microstructural analysis indicates that the influence of mica on the responses of mixtures originates from the intrinsic nature of mica as well as the particle packing being formed within WGS. Mica exists in the mixture as stacks of plates that form a spongy structure with high compressibility and swelling potential. Pores among the plates give the soil high water retention and high Atterberg limits. Large pores are also generated by soil particles with bridging packing, which enhances the permeability and water-soil interactions upon immersion. This study provides a micro-level understanding of how mica dominates the behavior of WGS and provides new insights into the effective stabilization and improvement of micaceous soils.