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. Studies can for example be made of the following: The anisotropy of soil samples. The effects of principal stress rotation. The effects of intermediate principal stress. The SS-HCA has been designed to be a high quality, low cost hollow cylinder apparatus. It has specifically been designed to be capable of testing at very small axial strains (down to 0.00004%).

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