The Energy Characteristics of Columnar Jointed Basalt Size Effect Considering the Occurrence Sequence and Magnitude of Micro-cracks.

The cumulative acoustic emission quantity and energy released when the columnar jointed basalts (CJBs) reach their strength under compression are important theoretical foundations for studying the mechanical characteristics of CJBs and for relevant engineering monitoring and reinforcement. Combining meso-mechanics of damage, statistical strength theory, and continuum mechanics, based on the DIC-improved RFPA digital image processing, the images of CJBs with different model sizes are constructed and transformed into heterogeneous finite-element mesh models to investigate the strength and deformation characteristics, fracture patterns, and energy progression laws of CJBs under uniaxial compression and lateral pressure conditions. The impacts of diverse factors on micro-crack quantity index (MCQI) and micro-crack energy index (MCEI) are analyzed. Furthermore, the main sensitive factors are identified through sensitivity analysis, establishing their fitting models. This study shows that the CJBs with larger joint elastic moduli (or rock constitutive relations tending towards brittleness) release MCEIs earlier. In addition, the CJBs owning larger column diameter may discharge MCEIs earlier, but with lower values, which is attributed to the scenario that under lateral pressure condition, the failure mechanism of large-diameter CJBs is mainly controlled by a small number of damage fracture zones. Moreover, the CJBs with joint constitutive relation tending towards plasticity (or greater rock homogeneity / stronger constrained state of rock mass) liberate MCEIs relatively late. Under lateral pressure condition, large-sized specimens with weaker boundary constraints have higher MCEIs because they are more prone to damage, and their larger size results in more damaged elements. Considering the occurrence sequence and magnitude of micro-cracks in CJBs, the factor sensitivity evaluation models for energy characteristics are constructed. Under lateral pressure condition, the main sensitive factors affecting MCEIs are the constrained state of rock mass, joint mechanical property, and rock heterogeneity. Conversely, the factors such as joint constitutive relation, column diameter, and meso-rock constitutive relation are less sensitive. The main sensitivity factor models for the MCEIs of CJBs can provide theoretical framework for engineering monitoring, reinforcement, operation, and maintenance of CJB engineering projects. Highlights: The larger the model size, the earlier the micro-crack quantity index and micro-crack energy index may appear on the strain axis. Under the lateral pressure condition, although generally a larger model size results in a higher micro-crack energy index, there are the exceptions. The main sensitive factors for the micro-crack quantity index are joint constitutive relation, rock mass constraint state, and column diameter, etc. The main sensitive factors affecting micro-crack energy index are the rock mass constraint state, joint mechanical property, and rock heterogeneity, etc. [ABSTRACT FROM AUTHOR]