Abstract: The micro-scale mechanical behavior of granular soils (e.g., particle movement and particle breakage, etc.) governs their macro-scale stress and strain behavior, such as strain localization and stress hardening, etc. To study the micro-scale mechanical behavior of granular soils, a mini-triaxial apparatus is developed in this paper. The axial loading system of the apparatus is composed of a servo-controlled stepping motor and turbine-driven reducer. The confining pressure is provided by a GDS pressure generator, and the chamber is fabricated with a highly transparent material with high strength and low density. In conjunction with an X-ray micro CT image processing and analysis techniques, this apparatus can be used for non-destructive detection of the micro-scale characteristics of a mini dry sample (i.e., 8 mm in diameter and 16 mm in height) under triaxial shearing. A triaxial test of a Leighton Buzzard sand (LBS) sample with an initial grading of 0.60-1.18 mm under a confining pressure of 1.5 MPa is carried out using this apparatus. The results show a reasonable stress-strain curve and CT images with easily distinguishable features, which demonstrates that the apparatus can be used for testing of the micro-scale mechanical behavior of granular soils.

Key words: mini-triaxial apparatus, X-ray micro CT, non-destructive detection, micro-scale mechanical behavior