Study of localized deformation in geopolymer cemented coal gangue-fly ash backfill based on the digital speckle correlation method

Uniaxial compression testing was combined with the digital speckle correlation method (DSCM) to explore the deformation field evolution characteristics and the Poisson’s ratio and energy release responses of a geopolymer cemented coal gangue-fly ash backfill (GCGFB) sample under uniaxial compression. The results showed that in the initial stage of loading, the deformation of the GCGFB sample was small and evenly distributed, and no localized deformation zone formed in the sample. As the loading progressed, a localized deformed zone gradually appeared, and the formation rate gradually accelerated. The maximum shear strain value at the start of localized deformation was 0.06. In the post-peak loading process, the localized deformed zone gradually expanded, and the degree of unevenness of the localized deformation was much greater than that before the peak; the maximum shear strain value at this time was 0.22. During the localization of the deformation to the peak intensity stage, the growth rate of the Poisson’s ratio of the GCGFB sample was markedly increased, and the growth rate after the peak was notably slowed and exhibited unstable fluctuations. When the stress reached the peak, the Poisson’s ratio was 0.24. The peak strain of the GCGFB sample was large, and the failure characteristics of the GCGFB sample showed multiple shear deformation zones, which is indicative of a typical cylindrical splitting failure. The deformation energy density of the GCGFB sample exhibited a slow decline after the peak, and the rate of decline gradually decreased. The deformation energy density drop time of the GCGFB sample was 96 s, which is much longer than that of high-strength rock.