Mechanical damage of an anisotropic porous rock in cyclic triaxial tests

This paper presents an extensive laboratory investigation of the mechanical properties of a porous sandstone which exhibits transversely isotropic behaviour. Particular attention has been paid to the influence of the structural anisotropy on the progressive development of pre-peak damage. Uniaxial and triaxial cyclic tests were performed for several orientations of the isotropy planes with respect to the principal stress directions in order to quantify the irreversible strains and the changes of oriented moduli with the cumulative damage. Two main mechanisms are involved throughout the loading process: compaction and microcracking. Compaction is active at all stress levels. In the uniaxial tests, both mechanisms are shown to be strongly influenced by the inclination of loading with respect to the isotropy planes. However, with increased confining pressures, the influence of anisotropy is significantly reduced.