Investigation into the Strength Properties of Layered Cemented Backfill under Various Loading Modes

With the normalization of deep mining and the large−scale application of backfill mining methods, underground stopes are often constrained by preparation capacity and backfilling processes, necessitating multi−stage layered pouring. This inevitably leads to the formation of layered interfaces within the backfill, which have become critical weak links affecting the long−term stability of stopes. To investigate the evolution law of mechanical strength of layered cemented backfill and ensure the long−term load−bearing stability of backfill in underground stopes, full tailings cemented backfill with different mass concentrations, numbers of layers, and layered interface dip angles was taken as the research object. Comparative tests of conventional uniaxial compression and incremental cyclic loading compression were carried out, and the influence law of multi−factor coupling on the backfill strength was systematically analyzed. The results show that the existence of layered interfaces significantly weakens the load−bearing capacity of the backfill. The peak strength of the backfill under both conventional compression and cyclic loading compression decreases gradually with the increase of the number of layers, with a maximum reduction of 28.42% for the three−layer specimen compared with the homogeneous specimen. The strength of the two−layer specimens continuously weakens with the increase of the layered interface dip angle, with a maximum reduction exceeding 12% at a dip angle of 10°. The peak strength of the backfill under cyclic loading compression is superior to that under conventional uniaxial compression, with an increase of 7%−21%. This enhancement is attributed to the elastic rebound during unloading, which effectively alleviates internal stress concentration and compacts micro−defects. Furthermore, the higher the mass concentration, the better the strength and anti−deterioration ability of the backfill. The research results reveal the comprehensive influence mechanism of layered interfaces and loading modes on the mechanical properties of backfill, and provide reliable experimental and theoretical support for the optimization of layered backfill processes, scientific mix proportion design, and stope stability evaluation in mines.