This study establishes a procedure to determine the level of anisotropy of unbound aggregatesystems based on particle geometry, mechanical response and physio-chemical properties of the fine aggregateportion (particles smaller than 75μ) of the aggregate system. Stress induced directional dependency of materialproperties based on multiple variable dynamic confining pressure (MVDCP) stress path tests was determinedfor ten aggregate sources. Anisotropic responses for various gradations and saturation levels were determinedfor each aggregate source. The cumulative Weibull distribution function is used to describe aggregate sizeand aggregate geometrical characteristics. The fine portion of the gradation was characterized by the Rigden voidstest and methylene blue test to account for fine particle shape properties and deleterious effect of plastic fines,respectively. Cross-anisotropic modular ratios are used as indicators of the level of anisotropy. The anisotropymodel is developed based on a comprehensive aggregate matrix consisting of twenty seven aggregate featuresfor sixty three aggregate systems. The sensitivity analysis of the model reveals the significant impact of particlegeometry on level of anisotropy and orthogonal load distribution capacity of unbound aggregate systems. Themodel is also shown to be sensitive to the level of bulk stress and shear stress as reflected by the k_2and k_3parameters.
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