Flow characteristics of moist-mixed materials for shotcrete: From experiment to CFD-DEM simulation

Abstract

Moist-mixed materials for shotcrete is an effective way to solve the volume control of shotcrete equipment in small and medium cross-section tunnels. The material of moist-mixed materials for shotcrete is characterized by cross-scale particle composition, and the problems of difficult dust control and short conveying distance remain unsolved. The pneumatic conveying simulation of the moist-mixed materials for shotcrete is studied using the CFD-DEM method. At the same time, a pipeline test system is designed, and the effectiveness of the CFD-DEM coupling model is verified by comparing the pressure drop and flow pattern with the field experiment. The model is used to study the pressure drop characteristics under different tilt angles, lifting angles, bend diameter ratio, and bend angle, involving three aspects: pressure drop in acceleration section (PDAS), unit pressure drop in stable section (PDSS), and energy loss caused by the elbow (ELE). The pressure drop model of pneumatic conveying of moist-mixed materials for shotcrete is established, and the relationship between the PDAS, PDSS, and ELE is obtained. The relationship between the Froude number and solid-gas ratio is clarified, and the calculation formula of maximum feed rate or minimum air flow rate is deduced. The velocity and spatial position distribution of particles at different tilt and lifting angles are revealed, and the elbow's main wear areas and wear rates at different bend angles and bend diameter ratios are obtained. The fundamental research has realized the unification of experiments and numerical simulation. The pressure drop law brought can guide further research on long-distance pneumatic conveying of moist-mixed materials for shotcrete.