Effect of Loading Boundary Conditions in Plane Strain Mechanical Response and Local Deformations in Sand Specimens

This study investigates the effect of loading boundary conditions on the mechanical behavior of cuboidal sand specimens during plane strain (PS) testing. Deformation-controlled PS compression tests were performed with flexible boundaries (FB) on varying densities of sand. Further, rigid-frictional and rigid-lubricated boundary triaxial compression tests were performed on cuboidal specimens with aspect ratios of 21 and 11, respectively. The results of PS testing with the loading boundary of different relative rigidity indicate a significant change in the observed response. The relatively rigid boundaries along the loading direction tend to overestimate the stress ratio compared with those with FBs. The FB-PS tests in the present study reveal no softening behavior, unlike those exhibited in conventional triaxial tests with rigid end boundaries. The imposed kinematic constraints for PS tests resulted in higher friction angle values compared with the triaxial tests. Local strain evolution and various deformation modes were analyzed using digital image analysis, which provides ensuing insights regarding its relation to the macro-scale global material response.