Macro- and micromechanical characteristics and energy evolution law of micro/nano carbon fibre grouting samples

Abstract

This study comprehensively explores the macro- and micromechanical attributes and energy evolution dynamics of micro/nano carbon fiber (CF) specimens. The investigation centers on a graded sand gravel grouting specimen, aiming to determine the optimal CF content through uniaxial compression tests conducted on samples containing 0.0 %, 0.5 %, 1.0 %, and 1.5 % CF. Utilizing CT and PFC2D simulation analyses, we establish the interrelation between micro- and macromechanics. The findings reveal similar failure modes across CF samples with varying contents, predominantly marked by shear failure in the principal crack of the inclined section, accompanied by proximal secondary cracks. The post-peak stress–strain curves exhibit notable divergences. Specifically, with increasing CF content, the total strain energy, elastic strain energy, and dissipated energy of the CF samples initially decline, subsequently rise, and then diminish once more. Furthermore, the 1.0%CF sample demonstrates heightened dissipated energy, uniaxial compressive strength, and elastic modulus in contrast to the 0%CF sample, showcasing superior macroscopic mechanical properties and enhanced toughness. A staged microcrack evolution unfolds, delineating defect initiation, pore evolution, crack development, and crack penetration stages. The non-uniform distribution of CF and sand gravel profoundly influences the propagation trajectory of minute cracks. Additionally, the failure modes and energy evolution trends from both models closely mirror experimental outcomes. The reinforcing characteristics and crack-resistant attributes of CF usher the transition from brittle failure (0%CF) to ductile failure (1.0%CF). PFC simulations highlight hysteresis in the model's damage and failure, underscoring CF's role in restraining grouting sample failure and shifting it from brittle (0%CF) to ductile (1.0%CF) failure, thus accentuating CF's pivotal role in impeding crack propagation. These findings furnish invaluable theoretical insights for bolstering grouting reinforcement in fractured rock masses.