Evaluation of stiff testing of rock

Abstract

When designing structures in rock, accurate and relevant information on the mechanical properties of the materials encountered is essential. While laboratory testing of rock materials provides some of the required data, it is important that the reliability and limitations of the information gained are fully understood. Tests on specimens with different height-to-diameter ratios from two materials of Class I and Class II type were evaluated to obtain a better understanding of the deformation behaviour of rocks in the post-peak region of the complete stress-strain curves. It was shown that the geometry of the test specimens influence the stress-strain behaviour in the post-peak region. The numerical values for the slope of post-peak graphs are thus not material constants per se, but are geometry dependent. Highly localized failure planes were observed for all the tested specimens with Class II type behaviour. Explanations for the observed phenomena have been proposed.