Full-field quantification of time-dependent and -independent deformation and fracturing of double-notch flawed rock using digital image correlation

The quantitative characterization of time-dependent and -independent deformation and fracturing of rock is crucial to reveal the short-term and long-term instability mechanisms of structural rocks. In the present paper, we conduct uniaxial constant strain rate and stress-stepping creep tests on double-notched sandstone samples with different rock bridge and flaw inclination angles. Full-field measurements of strain and crack evolution by using digital image correlation (DIC) are presented to understand time-dependent and -independent deformation, fracturing and associated crack types and failure modes of cracked rock. Results from uniaxial and creep experiments show that the flaw inclination, rock bridge inclination and time significantly affect the evolution of the strain field, and in turn change the crack propagation behaviour, and the final strength and failure mode of the rock. The vertical maximum principal stress direction is often in compression near the flaw tips, and as it moves away from the tip, the compression gradually changes to tension, while the parallel maximum principal stress direction is often in tension. Compared with short-term loading, tensile cracks such as wing cracks and far-field cracks, are prominent under creep loading conditions and can be fully developed and characterized by a longer expanded trajectory.

Automated summary

The quantitative characterization of time-dependent and -independent deformation and fracturing of rock is crucial to understand short-term and long-term instability mechanisms. Tests on double-notched sandstone samples show that flaw inclination, rock bridge inclination, and time significantly affect strain field evolution, crack propagation behavior, and final failure mode of the rock. Near the flaw tips, the stress direction is often in compression that gradually changes to tension as it moves away from the tip, while tensile cracks are prominent under creep loading conditions.