Evaluation of mechanical properties of mica-mixed sand considering inherent anisotropy

Abstract

This paper presents the effects of inherent anisotropy on the shear strength and shear modulus of both saturated and unsaturated sands. Several triaxial compression tests were performed using Toyoura sand with different contents of mica: 0%, 1%, 2.5%, 5%, and 10%. Specimens with various deposition angles α were prepared using the air pluviation (AP) and dry vibration (DV) methods. The shear strength properties were measured by conventional triaxial tests, whereas the small strain stiffness was measured by both local small strain (LSS) tests and bender element (BE) tests. The orientation of the sand particles was assessed based on two-dimensional optical microscopic measurements and mathematical estimation. The results showed that an increase in the mica content brought about a decrease in the degree of anisotropy of the shear strength because of mica particle breakage. However, the degree of anisotropy of the shear modulus became higher with a 0%–10% increase in the mica content. The shear modulus of the unsaturated sand had a slightly higher degree of anisotropy than that of the saturated sand. In addition, the degree of anisotropy of the shear modulus was assessed based on the average orientation angle θ of the sand particles.