Fluidity and Settlement Characteristics of Fresh Ultrafine Cemented Tailings Backfill under High Temperature Conditions

Mine depth increasing leads to the continuous rise of stope temperature. Under high temperature conditions, the fluidity of fresh ultrafine cemented tailings (UCTB) changes due to its influence, bringing potential safety hazards to pipeline transportation. In this study, UCTB rheological tests were carried out to analyze the effects of slurry temperature, mass concentration, and cement-sand ratio on UCTB rheological behavior. By using the numerical simulation method coupled with the particle tracking technology model, the pipe flow characteristics of UCTB were studied. Combined with the engineering background, the flow settlement mechanism of UCTB and the optimization of the number of filling inlets were clarified. Results showed that slurry temperature had an inverse relationship with UCTB plastic viscosity and yield stress and had a lower influence on rheological parameters than mass concentration. With the increase of slurry temperature, the flow nuclear velocity of UCTB increased, but the area of the flow nuclear area decreased, and the pipeline transport resistance loss decreased by about 12.3%. This indicated that increasing the slurry temperature was beneficial to improving the transportation efficiency of UCTB and reducing the wear degree of the pipeline. The UCTB flow in the stope was distributed as a parabola after settling. The sedimentation rate of UCTB particles and the content of coarse particles was the highest in the vertical position of the filling inlet. Extending from the inlet to both sides of the stope, the fine particle content increased and the settlement velocity decreased. Based on the mine parameters, when the stope length was 50 m–60 m, two filling inlets could improve the filling quality, and when the stope length was 70 m, three filling inlets could make the distribution of UCTB particles more uniform.