Study on Triaxial Progressive Failure and Energy Evolution Mechanism of Carbonaceous Layered Slate

Carbonaceous layered slate is a common metamorphic rock encountered in deep-buried tunnel construction in the southwest China,often leading to significant deformation and failure of tunnel surrounding rocks.Understanding the deformation and failure mechanisms of carbonaceous layered slate is crucial for maintaining the stability of surrounding rocks during tunnel construction and operation.To investigate the triaxial progressive failure and energy evolution mechanisms of carbonaceous layered slate,this study first conducted mineral composition analysis,microstructural scanning electron microscopy,and conventional triaxial compression tests on rock samples.Then,the mechanical response,microcrack propagation process,and energy evolution mechanisms of carbonaceous layered slate under different confining pressures were analyzed using Particle Flow Code (PFC) simulations,revealing the failure mechanism and energy dissipation characteristics.The results show that carbonaceous layered slate mainly consists of quartz and clay minerals and exhibits a distinct foliated structure.As the confining pressure increases,the peak strength and plastic deformation capacity of the slate significantly improve,indicating a suppression effect of high confining pressure on microcrack propagation.The accumulation of microcracks follows an “S”-shaped curve,with shear cracks primarily developing along the foliated planes and concentrating at 60° and 120° directions.With increasing confining pressure,the boundary energy and dissipated energy of the slate significantly increase,while the degree of particle frictional sliding intensifies,leading to a substantial increase in energy dissipation.This study provides valuable theoretical insights for addressing the issue of large deformation in surrounding rocks during tunnel engineering construction in similar rock formations.