Abstract: Sand, as a kind of typical natural granular material, its special mechanical behaviors, such as compressive hardening, dilatancy, anisotropy, etc., are controlled by the internal meso-fabric and its evolution. How to quantify the meso-fabric by experiment and numerical simulation is essential to further study the deformation mechanism of sand. The optical measurement technique based on relevant digital image methods is combined with soil test; and then a measuring system named “meso instantaneous optical system for sands deformation”, which can preliminarily achieve the macro-and meso-mechanical behaviors of soil, is developed by visually upgrading the shear box. The laboratory meso-diret-shear tests for Fujian standard sand are carried out by using this system. And then, numerical direct shear tests based on the software of particle flow code in two dimensions (PFC2D)are performed; and some meso-information which are difficultly obtained from laboratory test are extracted as its supplement. The test results of macro-and meso-mechanical behaviors including displacement field, strain field, particle orientation, velocity field, coordination number and force chain are compared and analyzed; and then the meso-mechanism of sand mechanical behavior is further studied.

Key words: sands, digital image correlation method, direct shear test, particle flow code, macromechanical properties, meso- mechanism