# Experimental Study on Horizontal Pipeline Transportation Characteristics of Coarse Particle
## 1 Introduction  
Dredging is a long-established construction technique that involves the excavation of soil and rock from the bottoms of rivers and seas using either manual labor or machinery and transporting the excavated materials to designated areas [1]. Due to the complexconstruction environment and the varying skill levels of construction personnel, high-concentration delivery is often not feasible during the construction process, resulting in relatively high construction costs [2]. Currently, dredging projects commonly utilize methods such as pipeline hydraulic transport, land transportation, and waterway transportation for the movement of dredged materials. Among these, pipeline hydraulic transport is widely used in large-scale dredging operations due to its advantages of high efficiency, low cost, and low energy consumption [3]. Therefore, studying the motion of the solid-liquid two-phase flow of coarse-grained dredged materials in horizontal pipelines is of significant reference value and practical importance for improving the hydraulic transport efficiency of pipelines and promoting applications. Currently, most studies rely primarily on experiments. Early theoretical models were based on macro-experimental summaries of pipeline transport characteristics. [PERSON] [4; 5] used a two-phase flow model, treating fine particles and water as the carrier, while considering large-diameter coarse particles as the transport object. They fully took into account the flow patterns of solid-liquid two-phase flow to derive the resistance loss of the two-phase carrier and the resistance loss of bed-load sediment transport. Several studies from the Saskatchewan Research Council have continuously improved the two-phase flow model and proposed the new model [6; 7]. The model is based on the Coulomb friction assumption, placing the particles causing friction in the lower layer while other particles are uniformly suspended in the pipeline. The model considers various factors, such as the pipe diameter, particle size, flow velocity, etc., and has high computational accuracy. [PERSON] and [PERSON] [8; 9] proposed a complex concentration distribution calculation model [10] that comprehensively considers the effects of the particle size distribution and volume concentration, which can significantly improve prediction accuracy and fit a larger particle size distribution. The most comprehensive model currently available internationally is the Delft head loss and critical velocity framework proposed by [PERSON] [11; 12; 13]. This model framework provides a more detailed description of the flow types of materials transported inside the pipeline and comprehensively considers the types of energy loss and the effects of interfacial forces. The model has a wider range of applicability and can be used for more complex pipeline layouts. [PERSON], [PERSON] [14], and others used high-speed cameras and particle imaging velocimetry technology to conduct a more intuitive analysis of the particle bed layer. They pointed out that the velocity distribution of particles in the cross-section is logarithmic and particles in the center of the cross-section of the pipeline flow are the largest, and those close to the top of the pipe wall flow are the smallest. [PERSON] [15] analyzed the particle motion behavior using methods such as acoustic emission, pressure pulsation, and high-speed imaging, revealing the formation mechanism of the minimum conveying speed, realizing the identification of complex flow patterns and quantitative detection of the solid mass flow rate/concentration across flow patterns, and establishing an intelligent prediction model for the solid mass flow rate in the horizontal pipe pneumatic conveying process. In summary, the research of most scholars and institutions mainly relies on experimental research methods. Early theoretical models were based on macroscopic experimental pipeline transportation characteristics, with an insufficient theoretical basis.