Influence of the loading conditions on the mechanical response of granular materials as constrained from experimental tests on synthetic rock analoguematerial

An extensive program of axisymmetric compression and extension tests was performed with synthetic granular, cohesive, frictional and dilatant, low strength/rigidity rock analogue material. The program was motivated in particular by the lack of rock tests under extension, and was aimed at a detailed characterization of the constitutive properties, and their dependence on loading conditions. This dependence was shown to be very significant particularly regarding the conditions of brittle–ductile transition and orientation of failure plans. In the extension tests, the above transition occurs at a mean stress σ that is 1.7 times greater than in compression tests, which corroborates the early results of Heard (1960 [1]) on Solnhofen limestone. The dilatancy factor β is larger under extension than under compression, and in both cases rapidly reduces with σ. The reported results can be used for improving the constitutive description of rock-like granular materials.