Development and application of a 2D biaxial compression test system for granular materials

A set of two-dimensional biaxial compression test system was developed to investigate the stress-strain behavior and its variation with the micro-fabric for granular materials.During testing a specimen was assembled using very small metal bars with elliptical sectional shapes and then was loaded in both horizontal and vertical directions.Three different stress paths,including constant lateral pressure,constant mean principal stress and constant principal stress ratio,could be easily realized.A new method of non-invasive measurement using both digital photo technology and image correlation analysis was developed so that the displacement of each metal bar in the specimen could be truly traced and as a result the displacement field of each specimen and its micro-fabric evolution during application of loading could be measured with a high degree of accuracy.The new test system was applied in monotonic shear tests for two-dimensional assemblies of mental bars with different elliptical sections,showing its essential effectiveness for the investigation of the micro-fabric variation and mechanical behavior.