Aiming at the backfill with prefabricated fracture under seepage‐stress coupling, the concepts of fracture macrodamage, loaded mesodamage, seepage mesodamage, and total damage of backfill were proposed. Based on the macroscopic statistical damage model, the coupling effect of seepage, stress, and initial fracture was considered comprehensively and the damage model of backfill with prefabricated fracture under seepage‐stress coupling was established. The mechanical properties of backfill with prefabricated fracture under different seepage water pressures and confining pressures were tested and the rationality of the model was verified. The research shows that the mechanical properties of backfill with prefabricated fracture under the seepage‐stress coupling are determined by the seepage water pressure, the load, the initial fracture, and the coupling effect. Fracture and seepage have significant effects on the damage of the backfill. When the seepage water pressure is low, the fracture damage dominates; however, when the seepage water pressure is high, the seepage damage dominates; the total damage under the coupling action is more serious than the single factor. The development laws of the total damage evolution curves under different seepage water pressures and confining pressures are basically the same, and they show the S‐shaped distribution law with the increase of the axial strain. With the increase of confining pressure, the damage effect of fracture and seepage on the backfill is weakened, indicating that the confining pressure has a certain inhibitory effect on the damage evolution of the backfill. The research results can provide a theoretical basis for the study of the stability of backfill with geological defects such as joints and fractures in deep high‐stress and high‐seepage water pressure coal mines.

To study the coupled degradation effects of disturbance damage and dry-wet cycles on backfill, cemented paste backfill (CPB, a mixture of coal gangue, fly ash, cement and water) samples with disturbance damage were prepared by cyclic disturbance loading tests. Subsequently, uniaxial compression tests were performed on CPB samples subjected to both disturbance damage and dry-wet cycles. Combined with the discrete element method, this study systematically explores the mechanical behavior and meso-degradation mechanisms of CPB under the coupled action of dry-wet cycles and disturbance damage. The research shows that: ①The cyclic disturbance loading will cause disturbance damage on CPB samples, and as the number of disturbances increases, the degree of damage gradually increases, and the two are exponentially related. ②There is a dry-wet cycles threshold value (5 times) for CPB samples. Below the dry-wet cycles threshold, the strength of CPB increases gradually with increasing dry-wet cycles. Above this threshold, however, dry-wet degradation occurs, and the elastic modulus degrades more significantly than the peak strength. ③The impact of disturbance damage diminishes with increasing dry-wet cycles. ④Under the coupled effect of disturbance damage and dry-wet cycles, the bind force between particles in CPB samples decreases, the energy absorption and storage capacity decreases, the frictional energy consumption increases, internal pores and microcracks initiate and develop, and the internal structure changes from dense to loose porous. The research results can effectively promote the development and application of backfill mining technology in coal mines.