Experimental evaluation of the anisotropic critical state theory for sand using 3D fabric evolution data of triaxial experiments

The critical state theory has been widely implemented in many models to predict the constitutive behavior of clayey soil. However, the notion of a unique critical state locus for sand/granular materials has been questioned in the published literature, suggesting the contribution of other microscale input variables represented by what is known as material fabric. Many numerical and experimental studies have quantified fabric reconstruction in rudimentary granular materials (i.e., 2D disks and spheres) in an attempt to incorporate fabric as an essential variable for CS attainment, which led to the development of the anisotropic critical state theory (ACST). Yet, no published literature has experimentally evaluated the ACST when implemented in 3D for natural sands. This paper evaluates the ACST for natural sand by incorporating the reconstruction of 3D normal to contact vectors between particles as measured using 3D imaging of in situ synchrotron micro-computed tomography scans that were acquired for conventional triaxial compression (CTC) experiments. The comparison between model predictions and experimental results advocates for the ability of the ACST to accurately predict the stress-dilatancy relationships of sheared sand specimens under different stress levels and initial density states.