Multi-scale crack propagation and damage acceleration during uniaxial compression of marble

The macroscale fracture of rocks is a progressive process consisting of the initiation, propagation, and coales-cence of numerous microcracks. In general, problems regarding the microscopic and mesoscale characteristics of the crack propagation evolution process of the intact specimen and prefabricated crack specimen, the intrinsic physical control factors of the critical acceleration of the near-failure damage, and the rock damage prediction analysis are difficult to solve. This study investigated the micro-and meso-damage evolution characteristics based on the scanning electron microscopy (SEM) tests of marble specimens under compression. The propagation and evolution characteristics of microcracks at different locations in marble specimen under load were analyzed based on the SEM image. In addition, the microcrack and mesocrack propagation qualitative analyses of the marble specimen under different loadings were performed. Using a multi-scale damage mechanics model and a newly constructed geometric model that reflected the crack propagation evolution, the macroscopic strain function of the geometric parameters of the damage and crack under loading was derived. The factors influencing the acceleration of crack development were revealed, along with the basis of the relationship between the evolution of damage and fracture parameters and external loads over different scales. The SEM timely crack propagation experimental results of the intact and pre-formed crack samples verified and illustrated the correlation. Although the different samples presented different damage expansion characteristics and varying warning levels before instability, common features were observed at the critical locations. This study aimed to generate a warning for possible larger fractures under different engineering conditions to establish a fundamental research foundation for the safety and stability of engineering projects.