Insight into the fracture mechanical properties of the interfacial transition zone of cemented coal gangue backfill under different stress angles by mesoscopic digital image correlation

The interfacial transition zone (ITZ) exists between the coal gangue aggregate and the cement-fly ash matrix in the cemented coal gangue backfill (CCGB). The ITZ is considered to be the weakest part of the mechanical properties of the CCGB, and its fracture is a precursor of the overall failure of the CCGB during the load-bearing process. In this study, small-sized cubic specimens with different stress angles (0 degrees, 45 degrees, and 60 degrees) were prepared using regularized modeling, and the effects of stress angle on the fracture mechanical properties of ITZ were investigated using mesoscopic digital image correlation (DIC) from laboratory tests and numerical simulations, respectively. The damage criterion of ITZ fracture was established based on fracture toughness, and the prevention and control measures of ITZ fracture were proposed. The results showed that the fracture mechanical properties of ITZ deteriorate and then recover as the stress angle increases. At a stress angle of 45 degrees, the initial fracture of the ITZ occurs first. The numerical results showed that the stress concentration areas are located at the top corners of the aggregate and adjacent ITZs on the side with the larger inclination angle, and the force chain is most widely distributed at a stress angle of 45 degrees. The ITZ is relatively more susceptible to failure under mode II fracture.