# Experimental Study on Horizontal Pipeline Transportation Characteristics of Coarse Particle
## 5 Conclusions  
This paper takes the pipeline hydraulic conveying of dredged material in the field of dredging construction as the research and application background, adopts the method of experimental research, designs and builds the experimental platform of horizontal pipeline hydraulic conveying of coarse particles on its own, and analyzes the effects of the particle diameter and material volume concentration on the velocity distribution of the coarse particle group flow pattern and the particle bed by combining the experimental images, data, and the observed macroscopic phenomena. The main conclusions are as follows:  
1. In horizontal circular pipe flow, the velocity distribution of each flow type has an overall symmetrical distribution, with the highest velocity in the central region, while the velocity of coarse particles in the upper and lower regions of the pipeline gradually decreases with an increasing distance from the centerline of the pipeline. There is a significant difference in the followability of particles with water flow, and particles near the centerline of the pipeline are more susceptible to the acceleration of water flow. The 0.9 mm diameter particles are more likely to complete the transition of the coarse particle group flow pattern. 2. The granular bed exhibits three main motion states: static sedimentation, displacement, and suspension under different operating conditions, with the static sedimentation layer accounting for a larger proportion in the low-speed region; The particles in the moving layer are tightly arranged and pushed forward as a whole through rolling or horizontal movement. The suspended moving layer mainly appears under high flow velocity conditions, and the particle distribution inside the pipe is relatively uniform. In addition, an increase in the material volume concentration and an increase in particle size will both cause the expansion of static sedimentary layers and delay the transition of flow patterns during translational motion. Therefore, when transferring dredged material via pipeline hydraulic conveyance, the concentration of dredged material should not be too high in order to avoid the emergence of an excessively thick sediment layer. 3. The range of particle starting speed variation is relatively small and always below 0.5 m/s. It is greatly affected by the average mixing speed, and the critical sedimentation speed is sensitive to changes in particle diameter and material volume concentration, showing a certain linear correlation as a whole. The transition of the coarse particle group flow pattern from the sedimentation bed type to translational motion is closely related to the particle diameter and material volume concentration. Coarse particle groups with a low material volume concentration and small particle diameter are more likely to complete the flow pattern transition. Therefore, when transferring dredged material via pipeline hydraulic conveyance, the water flow rate can be increased to achieve a reduction in the concentration of dredged material, thus avoiding blockage of the pipeline. 4. The range of the material particle size and the range of the maximum flow rate are limited in this study, and future research can further expand the range of the material particle size and the range of the maximum flow rate, as well as increase the number of experimental groups, so as to more comprehensively analyze the influence of relevant factors on the particle motion state. In view of the complexity of the pipeline arrangement in the actual dredging construction, future research can focus on exploring the mechanism of the influence of various factors on the movement and resistance characteristics of coarse particles in the pipeline under complex pipeline conditions. In addition, the influence of other factors such as pipe material and pipe geometry on the flow pattern and hydraulic gradient of the coarse particle population can also be studied in depth.