Constitutive behavior of binary mixtures of kaolin and glass beads in direct shear

Abstract

Composite soils having a wide range of particle size may be the most commonly encountered materials in geotechnical engineering practice. This study involves 21 direct shear tests to investigate the constitutive behavior of composite soils within the normal stress range from 50 to 200 kPa. The samples are mixtures of fine (kaolin) and coarse (glass beads) fractions at various proportions. The properties of the samples considered in the investigation are particle size distribution, water content of sheared specimens, structural features of shear surface and residual shear strength. It is shown that the particle size distribution influences the void ratio produced with the same compaction effort. Increasing fine fraction from zero to a threshold value (approximately 20–30%) causes a decrease in void ratio of the mixture. Beyond this threshold, a further increase of fine fraction causes an increase in void ratio. High proportion of fine fraction causes: (1) lower water content of shear zones relative to outer zones, (2) densification process within shear zone, (3) well slickensided shear surfaces, and (4) shearing in sliding mode and hence low residual shear strength.