Abstract: To investigate the mechanical properties and failure characteristics of fly ash as a cementitious material, uniaxial compression, acoustic emission (AE) and scanning electron microscopy tests were carried out on the cemented tailings backfill with fly ash replacing cement at 0%, 40% and 100%. Utilizing fractal and cusp catastrophe theory, we analyzed the AE parameters and strain energy parameters obtained during the loading process. We analyzed the variation characteristics of AE fractal dimensions and the early warning intervals associated with strain energy mutations during the cementation failure process for three different fly ash dosages. The results show that the hydration products of the cemented tailings backfill for each fly ash content primarily consist of ettringite and amorphous clustered calcium silicate hydrate. As the fly ash content increases, the quantity of hydration products, compactness, and integrity decrease. The strength of the specimens exhibits a decreasing trend, while the elastic modulus initially decreases and then increases. The mutation regions in strain energy for cemented tailings backfill at each fly ash content occurred prior to the stress peak and exhibited two distinct changes. Local failure intensification in specimens with 0% and 40% fly ash content was concentrated after the stress peak. Prior to overall failure, the fractal dimension exhibited a downward trend, with the warning interval situated in the middle to later stages of the fractal dimension decrease area. Local failure in the 100% fly ash content specimens intensified and concentrated before the stress peak. The fractal dimension exhibited an upward trend prior to overall failure, with the warning interval positioned in the initial and middle sections of the fractal dimension rising zone. The early warning intervals for cements with 0% and 40% fly ash content align more closely with the precursory characteristics of AE compared to those for cemented tailings backfill with 100% fly ash content. These research findings provide a theoretical basis for early warning regarding the failure of cemented tailings backfill.

Key words: fly ash, cemented tailings backfill, mechanical property, acoustic emission, fractal dimension, early warning interval