The flowability and mechanical properties are increasingly crucial in the filling process of deep metal mines with mining depths exceeding 1000 m. The rheological properties of filling slurry in the pipeline were analyzed through rheological tests, L-tube self-flow tests, and semi-industrial loop tests. The results revealed that with an increase in the cement-to-tailings mass ratio (c/t ratio) and mass concentration, the slurry exhibited a higher flow resistance and decreased stowing gradient. During slurry transportation, the pressure loss in the straight pipe was positively correlated with the slurry flow rate, c/t ratio, and mass concentration. A uniaxial compressive strength (UCS) test was conducted to analyze the mechanical properties of the cemented paste backfill containing BMC (CCPB) in both standard and deep-underground curing environments. The UCS of the CCPB showed an increasing trend with the rise in curing age, mass concentration, and the c/t ratio. The comprehensive analysis concluded that when the c/t ratio is 1:4, and the mass concentration is approximately 74%, and parameters such as the slump, bleeding rate, and flowability of the filling slurry meet the criteria for conveying and goaf filling, resulting in a high-strength filling body.

The stability of composite material that is composed of roof rock, cemented paste backfill (CPB), and floor rock has an important impact on safe mining within metal mines. In order to explore the mechanical properties, acoustic emission (AE), energy dissipation, and damage evolution of roof–CPB–floor (RCF) layered composite materials, uniaxial compression (loading rate 0.02 mm/min) AE tests on RCF materials with different CPB height ratios were performed. The test results show that: (1) the uniaxial compressive strength (UCS) and elastic modulus (E_R) of the RCF material were lower than those of the roof or floor rock and higher than that of the CPB. With the increase in the CPB’s height ratio from 0.2 to 0.7, the UCS and the E_R decreased from 18.42 MPa to 10.08 MPa and 3.15 GPa to 1.79 GPa, respectively, and the peak strain first decreased from 0.695 to 0.510 and then increased from 0.510 to 0.595. The UCS increased as a polynomial function with the increase in the E_R. (2) The AE ring count first increased slowly, then increased rapidly, and finally maintained a high-speed increase. The AE cumulative ring count at the peak point decreased with the increase in the CPB height ratio. The energy dissipation showed that the elastic energy U_E accumulated slowly at first, then the dissipated energy U_D increased, and finally the U_E decreased and the U_D increased almost linearly. The U_T, U_E, U_D, U_E–U_T ratio and U_D–U_T ratio showed a decreasing trend, and the U_E–U_D ratio showed an increasing trend at the peak point with the increase in the CPB height ratio. (3) Two damage constitutive models were established based on the AE ring count and energy principle. The damage evolution process of RCF materials can be divided into three stages: the slow damage accumulation stage, stable damage growth stage, and rapid damage accumulation stage.

In this study, the stage subsequent to filling mining is selected as the background, and the cemented tailings backfill serves as the research object. Given the effects of the layer effect, top load, lateral pressure coefficient, and so forth, a safety factor calculation model of cemented tailings backfill in large depth–width ratio stopes is developed in accordance with the Mohr–Coulomb failure criterion, which is compared with the models proposed by other scholars. Lastly, the characteristics of the effect exerted by a wide variety of factors are discussed. As indicated by the results, (1) there are three scenarios in the position of the sliding surface, located in the first layer, passing through two layers and passing through three layers, and mainly the first two. Compared with other models, the rationality and reliability of the model in this study are verified. Different models have different research backgrounds and different focuses, and certain differences exist in results. (2) The safety factor of cemented tailings backfills is reduced with the increase of the top load, the lateral pressure coefficient, and the bulk density, while it is increased with the increase of cohesion, internal friction angle, and bonding force ratio. Furthermore, a linear functional relationship exists between them. The safety factor has the maximum sensitivity to cohesion and the minimum sensitivity to top load. (3) Using Statistical Package for the Social Sciences (SPSS) software for regression analysis, a simplified multiple linear regression equation between the safety factor and the respective factor is built. The regression results achieve an error of 10%. As revealed by the result of this study, the simplified regression equation can be applied to the stability evaluation of the on-site cemented tailings backfill.

The curing temperature is one of the key factors determining the strength of cement paste backfill (CPB). This study investigates the effects of low curing temperatures (5, 10, 15, and 20 °C) on the hydration performance and hydration products of CPB and analyzes their impact on the macroscopic mechanical properties. The experimental results show that when the curing temperature of CPB is low, the reaction activity of cement clinkers such as C₂S and C₃S decreases, and the number of cement particles participating in the hydration reaction resulting in a reduced quantity of hydration products in CPB. At the same time, low-temperature inhibits the polymerization and connection of silicate chains, and short silicate chains remain stable under low temperature conditions, resulting in a decrease in the polymerization degree of CPB. As the curing temperature increases, CPB gradually transitions to brittle behavior, and the cohesion of CPB shows a linear increase trend, while the internal friction angle shows an exponential increase trend. When the curing temperature is low, there are often one or several cracks around the tailing particles, and these weak bonding surfaces lead to a decrease in the strength of CPB. The results of this study will contribute to a better understanding of the hydration behavior of CPB in low curing temperatures.

To investigate the impact of underground multiple stress disturbances on the long-term stability of cemented tailings backfill (CTB), this study conducted experiments under different disturbance levels (20–80% of static strength) and frequencies (1–4 times). By comprehensively utilizing mechanical testing, wave velocity monitoring, digital image correlation (DIC), and scanning electron microscopy (SEM), the “heterogeneous” evolution mechanism of macro-micro damage was revealed. The results indicate that disturbance level and frequency exert distinctly different driving effects on the deterioration of CTB, rather than a simple linear superposition. Specifically, low-frequency disturbance produces a compaction strengthening effect, microscopically promoting the generation of Ca(OH)₂ and ettringite (increased Ca/Si ratio). In contrast, the combination of high disturbance and high frequency induces free water extrusion and inhibits hydration, leading to an advanced damage threshold based on energy evolution and the accelerated coalescence of microcracks, which favors the formation of C-S-H gel (decreased Ca/Si ratio). Within this heterogeneous mechanism, the disturbance level acts as the dominant controlling factor. This study clarifies the nonlinear mechanical and chemical evolution paths under composite disturbances, providing theoretical support for the dynamic stability control of backfill in deep multi-step mining.

To address the inefficiency and data loss issues inherent in manual measurement, this study developed a full-time data extraction model for ultra-fine tailing slurry flocculation using Yolov8n. The performance of five flocculants—cationic polyacrylamide (YPAM), non-ionic polyacrylamide (FPAM), polyaluminum chloride (PAC), polymeric ferric sulfate (PFS), and a commercially used flocculant (KY)—was evaluated based on type, dosage, and pH. The model’s reliability was validated through slurry grayscale and clarification height analysis. Results indicate that the model enables automated data collection under varying lighting and viewing angles. YPAM was identified as the optimal flocculant across different pH conditions, improving the selection efficiency by 83% compared to manual methods.