Rheological properties and resistance evolution of cemented unclassified tailings-waste rock paste backfill

Coarse aggregate paste filling is the core direction of today’s mine development. The coarse aggregate filling can effectively reduce the discharge of the solid mine waste, which is conducive to the realization of safe, clean, and efficient mining of the deposit and can also reduce the production costs of infill mining and promote the coordinated development of green mining. To study the pipeline conveying characteristics of the tailing‒waste rock paste, the rheological properties were tested by a rheometer under different tailing‒waste rock ratios and solid content conditions. A resistance equation integrating the compactness, water‒cement ratio, and volume concentration was constructed. This was then brought into the Comsol software for simulations and compared with the actual measurement results of the ring pipe. Errors measured by the numerical model are verified to be all within 7%, indicating that the model reasonably calculated the resistance characteristics of the tailing-waste rock paste. Variation characteristics of the pipeline conveying resistance under different solid contents, tailing‒waste rock ratios, and initial velocity conditions were also simulated. Experimental results show that the plastic viscosity and yield stress increase with the solid content and tailing‒waste rock ratio. Due to the friction effect between the particles, the resistance loss tends to increase and then decrease with the tailing‒waste rock ratio. The increase in the solid content leads to a decrease in the water content of the paste, which consequently results in difficulty in the flow of coarse aggregate slurry and a rapid increase in the resistance loss. The initial flow rate increases, the particle motion becomes unstable, the friction increases, and the growth rate of the drag loss increases greatly after the “inflection point” of 2.2 m·s⁻¹. It is recommended that the mine should be filled with a tailing‒waste rock ratio of 5∶5 and an initial flow rate of 2.2 m·s⁻¹. The results have certain reference significance for the design of a coarse aggregate paste pipeline conveying system, which helps the development of coarse aggregate paste conveying technology and also has a positive effect on reducing the pipeline conveying resistance and extending the conveying distance.