Engineering geological characterization of micaceous residual soils considering effects of mica content and particle breakage

Abstract

The engineering geological characteristics of micaceous residual soil (MRS), which is prevalent in subtropical regions, are markedly influenced by the presence and breakage of mica particles. Nevertheless, a comprehensive understanding of the underlying mechanisms responsible for these effects remains elusive. In this study, a series of experimental tests were conducted on two groups of reconstituted MRS samples. These samples were prepared by mixing natural MRS, from which the original mica had been removed, with intact and crushed mica powder, respectively. The aim was to investigate the effect of the mica content and particle breakage on the physical and mechanical properties of MRS. Scanning electron microscopy was employed to scrutinize the microstructural alternations of mica particles at different states of breakage, and a conceptual model was proposed based on the observations. The findings revealed that the presence of mica considerably altered the physical properties of MRS, resulting in higher Atterberg limits but lower plasticity, along with unfavorable mechanical properties, including high compressibility and swelling potential, low compactability, stiffness, strength, and ductility. The microstructural analysis elucidates that these effects stem from the resilient nature of layered mica flakes with high water-retention capacity. On the other hand, the breakage of mica particles changed these effects. The disappearance of interlayered voids following mica particle breakage leads to reduced Atterberg limits and enhanced compaction efficiency of the mixture. Moreover, MRS with a higher proportion of crushed mica exhibited more significant deformation and compression during shearing. This behavior can be attributed to the diminished stiffness of crushed mica and weaker interparticle contacts within the soil matrix. This study provided a multi-scale insight into how mica affected the engineering geological properties of MRS and proposes references for more effectively incorporating of MRS into engineering construction projects.