The purpose of any soil mechanics apparatus in a laboratory is to duplicate the in-situ conditions. However, none of these apparatus can control the rotation of the principal stress-strain directions. Axis-symmetric triaxial tests cannot model these conditions (principal stresses can only be 0° or 90°) and conventional shear tests rotate the axis associated to the major principal stress but without the possibility of monitoring stress conditions.
Advanced material characterization requires a testing device capable of controlling the rotation of principal stress directions. The GCTS Hollow Cylinder Apparatus (HCA) is capable of imposing three-dimensional stress states, and it can rotate the principal stress directions.