Abstract—An accurate quantification of the grains’ arrangement and structure is the key to establish the relationship between microscopic and macroscopic properties for granular media, which is also of vital importance for precisely predicting macro-deformation and mechanical behavior using the system’s microscopic properties. In order to further reveal the structural characteristics of the granular media, a special loading device was designed and developed; then, the polycarbonate disk grains with the diameters of 3 mm and 5 mm were prepared for photo-elastic tests under complex loads. The relationship of the distribution frequency of the contact angle between grains with grain scale, grain combination as well as the magnitude and direction of the external load was explored. Results reveal that: (1) for granular media consisting of a single component, the geometrical structure shows obvious initial anisotropy without the application of load, the initial structure determines the transfer of force in the granular system; during the shearing process, the frequency distribution of the contact angle increased significantly along the directions of great main stresses but decreased along the directions of small main stresses. (2) for the mixed granular system consisting of grains with two different diameters, the anisotropy was not obvious, whether under initial conditions or under compression and shearing loads.
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