# Pressure Study on Pipe Transportation Associated with Cement Coal Gangue Fly-Ash Backfill Slurry
The solid content of the fresh CGFB slurry is 78.05% by weight (with water accounting for the remaining 21.95%) and is composed of Portland cement (10%), fly ash (20%), coal gauge (48%) and additive (0.05%) [5]. The main ingredient of the additive is hydroxyprop methylcellulose. Table 1 list the compositions of the coal gauge particle sizes used in the CGFB slurry configuration and Figure 1 provides the fly-ash and cement particle size distribution. The CGFB slurry was observed to exhibit non-Newtonian behavior [6]. A Bingham plastic model was found to be adequate for describing the slurry rheology at moderate shear rates [7; 8]. The pilot plant loop test with a horizontal pipe was conducted during the CGFB pipeline transportation, in which the average loss of frictional resistance per unit length was observed as 3.80 kPa/m, while the average loss of local resistance was 4.11 kPa/m [9; 10]. The maximum value which appeared in the monitor was 4.40 kPa/m and 4.78 kPa/m for the straight pipe transportation and the bend, respectively [9; 10; 11]. Under this level of transmission resistance, the CGFB slurry can be transported for a longer distance (over 3000 m) with a larger scale flow that satisfies the coal mine backfilling requirements [11]. In the slurry pipe conveying process, the friction between the slurry and the pipe wall, the interaction loss associated with the colloidal among the fine solid particles and the collision due to the slurry flow diffusion were concluded to be three aspects that compose the transmission resistance of high-concentration slurry [12]. In addition, the CGFB slurry pipe delivery length largely depends on the resistance loss that is produced during the process of the underground pipe transportation. Thus, understanding the slurry flow characteristics, predicting the slurry pressure loss and determining the reasonable transportation velocity is essential to ensure the safety of the CGFB slurry pipe transportation and reduce the risk of pipe blockage due to the high solid concentration. The value of the high-concentration slurry flow resistance loss in the pipeline is most influenced by the slurry rheological characteristics and hydraulic conveying velocity [13]. The slurry yield stress and relative viscosity contributes to the slurry initial rheology but the conveying velocity's impact on the resistance is not very clear. In the pipeline transportation process, an obvious difference is observed for the velocity distribution of the slurry flow along the slurry's movement forward because of the limitation of the pipe wall and the influence of the slurry's own rheological properties. The offset in the flow conveying velocity can cause the diffusion of the slurry. In addition, a large fraction of the drag stems from velocity fluctuations and globally 10% of all energy is used to overcome turbulent drag in one way or another [14]. Thus, the effect of the pressure drops and velocity distribution profiles needs to be studied thoroughly within the CGFB pipe transportation. According to this, this article has developed a study of the pipe transportation characteristics in the horizontal direction that is forced on the CGFB slurry with a solid concentration of 76.05% by weight. Computational fluid dynamics (CFD) have been used to predict the flow characteristics for a long time and the effects show great agreement with the experimental tests. The literature review shows that the pressure drop characteristics in the slurry pipeline have been successfully predicted universally using commercial CFD tools. [PERSON] et al. [15] studied the flow in a vertical pipeline for slurry flows with coarser particles. [PERSON] and [PERSON] [16] investigated sand-water slurry flows in the entrance region of a horizontal pipeline using CFD with the ASM model. [PERSON] et al [17] performed modeling of slurry pipeline flow shaving fine particles at higher solid concentrations using CFD.