Advances in research on the evolution of trans-scale discontinuous structures during the creeps of strongly disturbed coals

[Objective and Methods] Disasters associated with surrounding rocks in roadways, such as time-dependent deformation failure and creep-induced rock bursts, severely threaten deep mines in China. These disasters, coupled with the impacts of deep mining and structural changes, render it urgent to explore the evolutionary patterns of trans-scale discontinuous structures during the creeps of strongly disturbed coals. This study systematically reviews the scale effects of coals' mechanical properties, the discontinuous structures and multi-physics field effects of coals, and the long-term stability, creep evolutionary patterns, and mechanical models of coals. It highlights the close correlation between discontinuous structures (including their fractures and minerals) and physical and mechanical properties during the deformation and failure of different scales (mesoscopic, macroscopic, and engineering scales) and sizes (within the range of representative elementary volume (REV)) of coals. [Results and Conclusions] The results indicate that the trans-scale discontinuous structures of coals cause the nonuniformly distributed stress field, which results in mechanical anisotropy, scale effects, and size effects. Consequently, disharmonic macroscopic rupture will occur. The key to understanding the intrinsic disaster mechanisms of coals is the transparentized analysis and deduction of the evolutionary patterns of both trans-scale discontinuous structures and the multi-physics field during the deformation and rupture of coals. It is clear that existing creep experiments and models enjoy advantages in revealing the surface deformations and failure of coals. However, they fail to predict the deformations and discontinuous structures within coals. Hence, the authors of this study developed an approach that combines full-size computed tomography (CT) scanning and digital reconstruction, digital volume correlation (DVC), and trans-scale synthetic rock mass and grain-based modeling (SRM-GBM). This study explores the leading-edge issues related to the creeps of disturbed coals, introducing the new point of view that the creeps of coals are induced by internal deformation and damage caused by their discontinuous structures and stress. Accordingly, it proposes that discontinuous structures and stress serve as the dominant factors governing the disharmonic creeps of coals. Finally, this study developed new methods for fine-scale modeling and transparentized analysis for exploring the evolution of both trans-scale discontinuous structures and the multi-physics field during the creeps of strongly disturbed coals. The results of this study will lay the theoretical foundation for the occurrence mechanisms, early warning, and prevention and control of relevant mine disasters. © Editorial Office of Coal Geology & Exploration. OA under CC BY-NC-ND.