In the wall of a hollow cylindrical specimen under combined axial load, torque and internal and external radial pressures, the magnitude and direction of the major and minor principal stresses can be controlled together with the magnitude of the intermediate principal stress. This Paper describes both the design and principles of operation of a new hollow cylinder apparatus and its application to the investigation of principal stress rotation effects in sands and clays. A discussion is presented of the stress and strain nonuniformities which occur in a hollow cylinder specimen as a result of its curvature and of restraint at its ends. The manner in which these non-uniformities have been minimized, by selection of a sample geometry of 203 mm id. × 254 mm o.d. × 254 mm height and by the use of internal instrumentation, is described. The results of tests on dense Ham River sand are presented to demonstrate the capabilities of the apparatus. Dans la paroi d'un echantillon creux cylindrique sous une combinatio...