Experimental Study on Dynamic Characteristics of Cemented Tailings Backfill Under Different Tailings Gradation

The stability of cemented tailings backfill (CTB) is influenced by mining disturbance. As a property of CTB, tailings gradation (TG) is one of the factors that change its mechanical properties. Taking tailings gradation, impact amplitude, and curing age as variables, this paper focuses on the characteristics of the influence of curing age on the failure deformation, strength evolution, failure mode, and microstructure of CTB. The results show that with the average particle size of the tailings from coarse to fine, the peak stress and elastic modulus of CTB first decrease and then increase. The increase in curing age and impact amplitude can improve the elastic deformation capacity of CTB. During the post-peak phase, the stress–strain curve undergoes sequential morphological transitions, evolving from the initial “stress drop” characteristics through “post-peak plasticity” manifestations before ultimately demonstrating “post-peak ductility” behavior. This progression corresponds to CTB’s material transformation pathway, commencing as a rigid substance that first transitions into a plastic-brittle composite, subsequently develops plastic properties, and finally attains ductile material characteristics. The TG changes from T1 to T4, and the failure mode of CTB gradually changes from composite failure and shear failure to tension failure and composite failure. A CTB strength prediction model based on TG is proposed. The R² of the model is 0.997, F = 12,855, and p < 0.001, which has high applicability. As tailings vary from T1/T2 to T4, AFt content progressively decreases, the C-S-H gel transitions from a 3D network to a flocculent structure, and the skeleton shifts from coarse to fine particles, leading to increased porosity but smaller pores.