Subcritical Crack Growth and Progressive Failure in Carrara Marble Under Wet and Dry Conditions

Our concept of progressive rock slope failures is on the one hand embedded in aggregated subcritical crack growth mechanisms and on the other sensitive to environmental conditions, especially water. To anticipate failure dynamics in rock slopes, it is a key requirement to reveal the influence of water on subcritical crack growth mechanisms and material properties. We present experimental data on the time-dependent deformation of an exemplary rock, Carrara marble. We employed inverted single-edge notch bending creep tests on large Carrara marble samples to mimic an open joint system with controlled water supply. Constant stress was applied in two steps approaching 22-85% of a previously determined critical baseline stress. Introducing calcite-saturated water to subcritical stressed samples caused an immediate increase in strain by up to an order of magnitude. Time-dependent accumulation of inelastic damage at the notch tip occurred in wet and dry samples at all load levels. Subcritical crack growth and the evolution of localized intergranular fractures are enhanced if water is present and readily approach tertiary creep when loaded above 80%. The immediate strain response is attributed to the reduction of surface energy and diffusion of the water into the rock. The resultant more compliant and weaker rheology can even turn the subcritical stress into a critical state. Over time, subcritical and chemically enhanced mechanisms progressively alter especially grain boundaries, which become the key controls of progressive failure in Carrara marble.