Macro-meso fatigue failure of bimrocks with various block content subjected to multistage fatigue triaxial loads

Abstract

The non-linear mechanical behaviors of bimrock under static loading conditions have been widely studied currently. To data, however, the fatigue responses of bimrock with various rock block percentage (RBP) under multi-level cyclic loads were not well understood. The cyclic triaxial tests combined with post-test computed tomography scanning were employed to investigate the damage-cracking and volumetric dilatancy characteristics of a slope bimrock. The results reveal that multiple block-matric damage and volumetric dilatancy were strongly impacted by the block content. Bimrock strength and stiffness increase but volumetric deformation decreases with increasing block content. The occurrence of critical instability for bimrock with RBP is earlier than those with high RBP by the proposed volumetric strain rate. In addition, damage is larger for bimrock with low RBP and damage growth rate decreases accordingly. A two-stage damage evolution model was proposed to describe the damage propagation and the mode fits the testing data well. Moreover, the mesoscopic interface damage-cracking and volumetric dilatancy were visualized from CT images, two indices of interface damage ratio (IDR) and failed volumetric rock proportion (FVBP) reveal that the matrix expansion and interface cracking play a dominant role in volumetric dilatancy for bimrock with low block content. However, the block interlocking and occlusion contribute a lot to volumetric expansion of bimrock with high RBP, and their instability was limited at the confined condition.Through a series of macro-meso fatigue failure analysis, the effect of block proportion on bimrock under triaxial fatigue failure have been presented first. This study is in favor of predication the long-term stability of the bimrock slope under complex disturbed stress.