Macro-meso fatigue fracture and instability of rock-backfill composite structure under increasing-amplitude cyclic loading

• Published in: Construction & building materials Vol. 416; p. 135187
• Main Authors: Long, Dayu, Wang, Yu, Li, Changhong, Wu, Yunfeng
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 16-02-2024
• Subjects: CT scanning; Cyclic loading; Failure mode; Fracture evolution; Rock-backfill composite structure; Cyclic loading; Failure mode; CT scanning; Rock-backfill composite structure; Fracture evolution
• ISSN: 0950-0618; 1879-0526
• DOI: 10.1016/j.conbuildmat.2024.135187

The rock-backfill composite structure (RBCS) material in mine stopes is often subjected to stress disturbance. In order to reveal the fracture and instability mechanism of the RBCS exposed to disturbed stresses, a series of multi-stage cyclic loading tests were conducted on RBCS specimens with various cement-tailing ratios (c/t). The results indicate that deformation characteristics, stiffness degradation, damage propagation and failure mode of the RBCS were greatly influenced by the c/t. The volume dilatancy increases as well as the secant modulus (Es) increases and then decreases with decreasing c/t, i.e., from 1:4 to 1:12. For a sample with c/t of 1:4 and 1:8, the damage displays two-phase increasing pattern. However, for a sample with c/t of 1:10 and 1:12, inverted S-shaped damage accumulation pattern is found. As the c/t decreased, failure mode of RBCS specimens transformed from mixed tensile-shear failure to dominant tensile failure. Post-test CT imaging reveals obvious fracture evolution pattern that was characterized by shear fracture within the backfill, a circular tensile fracture along the rock-backfill interface, and tensile-shear fracture within the surrounding rock. It is noteworthy that complicated crack network is prone to forming for RBCS specimens with the c/t of 1:4 and 1:8. It is found that the use of "flexible CTB" with relatively low c/t is beneficial to improve the overall stability of the mine stopes.
•The influence of the c/t on fracture and instability of the RBCS samples was investigated.•Early warning of RBCS instability was realized by using the volumetric strain rate.•The deformation characteristics, stiffness degradation, damage evolution and fracture mode were influenced by the c/t.•Post-test CT images highlight the fracture of rock-backfill interface and the final instability pattern.