Experimental study on spatial evolution of mode-I and mode-II fracture toughness of cemented paste backfill under external sulphate attack.

External sulphate attack (ESA) interferes with spatial changes in fracture toughness of cemented paste backfill (CPB) and affects its mechanical stability. Large-scale curing column models are developed to investigate the spatial evolution of mode-I and mode-II fracture toughness (i.e. KIC and KIIC) under seepage- and diffusion-induced ESA. It has been found that the seepage-induced ESA leads to spatial changes in KIC and KIIC of CPB at advanced ages and higher extent of degradation of fracture toughness is measured at a deeper position in CPB. Comparatively, KIc can be used as a reliable quantity to estimate KIIc under the diffusion-induced ESA. [ABSTRACT FROM AUTHOR]