Assessment of nano-to-micro-scale geomechanical properties and their time-dependent behavior: Current status and progressive perspectives

Rocks can deform at varying scales (nano-, micro- and macro-scale) under different temperatures, pressures, stresses, and time conditions. Sub-core scale (nano-to micro-scale) changes in rock properties can influence local (fine-scale) and bulk scale (macro-scale) rock deformation. However, there is a lack of comprehensive knowledge on how rock deformation at sub-core scale (i.e., nano-to micro-scale) is assessed and its potential to accurately predicte and estimate the macro-scale mechanical behavior of rocks. This study presents a comprehensive and forward-leaning review of the assessment of nano-scale and micro-scale rock mechanical parameters, their time-dependent behavior, and potential applications in rock engineering. Also, we highlighted the key findings based on experimental and numerical methods for evaluating rock mechanical parameters, and presented the limitations of these approaches. Further, we discussed the reliability of sub-core scale mechanical assessments in predicting macromechanical (larger-scale) properties and the behavior of rocks in geo-engineering. Finally, we offer recommendations to advance investigations focused on rock mechanical assessments at these smaller scales and provide a more accurate characterization at the sub-core scale.