The thixotropic characteristics of rheological parameters of waste stone-tailings cemented paste backfill and the time effect of pipeline resistance

Abstract

The cemented paste backfill (CPB) involves the optimal combination of one or more solid materials with water to prepare a paste-like slurry with certain stability, fluidity, and plasticity. The paste flows as a piston flow under external force (pumping pressure) or gravity through pipelines into the underground goaf to complete backfilling operations. In order to improve the performance of the CPB, coarse aggregate is added to the CPB to form a coarse aggregate cemented paste backfill (C-CPB). The C-CPB belonged to non-Newtonian fluids and exhibited thixotropic behavior as its rheological parameters determined its flow characteristics. During the initial stage of pipeline transportation, the rheological parameters of the paste material were influenced by its thixotropic behavior and exhibited a certain degree of time dependence. The present study employed the stress relaxation method for thixotropy test to ascertain the rheological parameters of the C-CPB with respect to shear time. The results indicated that the yield stress decreased with increasing shear time with a negative exponential growth trend. A mathematical function describing the variation of yield stress with time for the paste material was established, and an estimation method for thixotropic equilibrium time of the yield stress was proposed. A Gaussian distribution function describing the variation of plastic viscosity with shear time was developed, and the thixotropic stabilization time of plastic viscosity was estimated. On this basis, a pipeline transportation resistance model considering the time-dependent rheological parameters of the C-CPB was established. Subsequently, a formula for calculating the boundary layer thickness during the initial stage of pipeline transportation was derived. The establishment of the model enables a better understanding of the resistance characteristics of the paste during the initial stage of pipeline transportation, as well as the process and patterns of boundary layer formation, which is of great significance.