The GDS Small-Strain Hollow Cylinder Apparatus (SS-HCA) allows for rotational displacement and torque to be applied to a hollow cylindrical specimen of soil. Using this device it is possible to control the magnitude and direction of the three principal stresses. The GDS SS-HCA can apply a uniquely wide range of stress paths on the test specimen. The loading systems are computer controlled and strains can be measured directly on the test specimen. These strains can also be servo-controlled.