Micromechanics of Fracture Propagation During Multistage Stress Relaxation and Creep in Brittle Rocks

• Published in: Rock mechanics and rock engineering 2022-12, Vol.55 (12), p.7611-7627
• Main Authors: Zafar, Sana, Hedayat, Ahmadreza, Moradian, Omid
• Format: Article
• Language: English
• Subjects: Acoustic emission; Acoustic emission testing; Civil Engineering; Compression; Crack initiation; Crack propagation; Cracking (corrosion); Cracking (fracturing); Cracks; Damage; Deformation; Digital imaging; Distribution; Earth and Environmental Science; Earth Sciences; Emission analysis; Engineering; Evolution; Experiments; Failure mechanisms; Failure modes; Fracture mechanics; Fracturing; Geology; Geophysics/Geodesy; Growth; Micromechanics; Original Paper; Rock; Rock deformation; Rock masses; Rocks; Shear; Solifluction; Strain; Strain analysis; Stress propagation; Stress relaxation; Time dependence; Yield point
• ISSN: 0723-2632; 1434-453X
• DOI: 10.1007/s00603-022-03045-w

Time-dependent rock deformation caused by the initiation and growth of fractures leads to the weakening of the rock mass. Understanding the fracturing mechanisms involved in the time-dependent behavior in brittle rocks is very important and to achieve this goal, a systematic series of three types of experiments was performed on double-flawed prismatic Barre granite specimens under unconfined compression. The first series aimed to identify the failure mechanism in the short-term failure mode under monotonic loading, the, second series involved multistage relaxation (constant strain) experiments to analyze the damage at different strain levels, and the third series explored the fracture propagation under multistage creep (constant load) experiments. The spatial and temporal evolution of cracking mechanisms were evaluated using the acoustic emission (AE) and two-dimensional digital image correlation (2D-DIC) techniques to observe the whole crack growth process as well as the accumulated inelastic strain at the specified region of interest. Results suggest that in the case of multistage creep experiments, the time to failure was less compared to the multistage relaxation, when loaded above the crack damage threshold (CD) estimated from the monotonic testing. The frequency magnitude distribution of the AE events generated in the three loading conditions followed the Gutenberg Richter model. A relatively lower b-value was obtained for the creep experiments, indicative of high energy AE events and faster crack growth. In addition, the AE and DIC results also revealed high evolution of tensile cracks at-different stages of creep and relaxation compared to shear and mixed-mode cracks. Highlights Fracturing mechanisms under multistage relaxation and creep experiments were identified. AE and DIC results showed high evolution of tensile cracks as compared to shear and mixed-mode cracks. Frequency-magnitude distribution illustrated a lower b -value in case of multistage creep as compared to multistage relaxation.