Abstract: A self-made hollow cylinder torsional apparatus for rock was developed to control four loading parameters independently, including axial force, torque, internal and external confining pressures. This study presented several stress paths and loading methods which were easy to implement in practical engineering projects and meet their requirements through mathematics and mechanics analysis. The tensile strength of rock can be obtained in the premise that the axial force and internal confining pressure satisfy specific relationships. By controlling the internal and external confining pressures and axial force, conventional triaxial tests and true triaxial tests can be carried out by using the hollow cylinder torsional apparatus for rock. Thus, the existing disadvantages of the complicated true-triaxial test apparatus and the large loaded surface friction were overcome. The mean stress p and the coefficient of intermediate principal stress b can be kept constant when the axial force and the internal and external confining pressures meet certain relationships, respectively. Those stress paths can be used to study the effect of the stress rotation on rock mechanical properties. Therefore, the realisation of the above stress paths is of great significance to the study of rock mechanical properties and the development of laboratory tests.

Key words: rock mechanics, principal stress rotation, hollow cylinder torsional apparatus, stress path