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.

中文翻译：

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废石尾矿胶结膏体充填体流变参数触变特性及管道阻力时间效应

胶凝膏体回填（CPB）是将一种或多种固体材料与水进行优化组合，制备具有一定稳定性、流动性和可塑性的膏状浆体。膏体在外力（泵压）或重力作用下以活塞流的形式通过管道流入地下采空区，完成回填作业。为了提高CPB的性能，在CPB中添加粗骨料，形成粗骨料胶结浆体回填体(C-CPB)。 C-CPB属于非牛顿流体，表现出触变行为，其流变参数决定了其流动特性。在管道输送初期，膏体材料的流变参数受其触变行为的影响，表现出一定程度的时间依赖性。本研究采用应力松弛法进行触变性测试，以确定 C-CPB 相对于剪切时间的流变参数。结果表明，屈服应力随着剪切时间的增加而减小，且呈负指数增长趋势。建立了描述糊状材料屈服应力随时间变化的数学函数，提出了屈服应力触变平衡时间的估算方法。建立了描述塑性粘度随剪切时间变化的高斯分布函数，并估计了塑性粘度的触变稳定时间。在此基础上，建立了考虑C-CPB随时间变化的流变参数的管道输送阻力模型。随后推导了管道输送初期边界层厚度的计算公式。该模型的建立可以更好地了解管道输送初期膏体的阻力特性以及边界层形成的过程和模式，具有重要意义。