## 1 Introduction  
Debris flow is a solid-liquid-gas mixture that occurs in mountainous areas, and its properties lie between those of water-laden flows and those of landslides, being it usually characterized by sudden outbreaks, fierceness, and strong destructive power [1; 2; 3; 4; 5]. Its catastrophic nature poses a significant threat to infrastructure, economic development, and lives and properties of people in mountainous regions, making it one of the main natural disasters in these areas [6]. Debris flow differs from water-laden flows and landslides; yet, it exhibits certain characteristics of both landslides and water-laden flows, due to its wide range of grain size distribution [7]. The wide grain size distribution causes significant internal resistance, influencing the transport characteristics of debris flow [8; 9; 10]. The rheological characteristics of debris flow, reflecting its structural properties and movement laws, affect the calculation of dynamic parameters, such as impact force and flow velocity, and are correlated with the erosion-deposition features and delineation of hazardous zones. Therefore, the rheological properties of debris flow remain an essential basis for researchers exploring its internal movement mechanisms [11; 12; 13].  
The influence factors of debris flows are very complex; they can basically be categorized into background factors and triggering factors. The background factors mainly refer to the mechanical characteristics of geo-materials, topography and landscape, and soil vegetation, while the triggering factors include hydrological and rainfall conditions and human activities. Numerous scholars so far have extensively researched the rheological characteristics and influence factors of debris flow, aiming to unveil its internal mechanisms. [PERSON] [14] and [PERSON] [15] employed granular flow theory to explain the shear mechanisms of debris flow. [PERSON] et al. [16] utilized large-scale rotating plate rheometers to conduct on-site tests on the viscous debris flow of Jiangjiagou, revealing phenomena like stress overshoot and shear thinning under low shear rates. [PERSON] et al. [17] analyzed the shear deformation of debris flow slurries with different maximum particle sizes, obtaining the variation rules of rheological parameters. The results indicated that mixing coarse particles with fine ones can enhance the yield stress of debris flow slurries, mitigating the occurrence of shear thinning. [PERSON] and [PERSON] [18] observed the transformation of suspensions from initially shear-thinning fluids to progressively shear-thickening fluids by adding sands of varying concentrations and particle sizes (<0.425 mm) into clay and silt suspensions. Based on the relationship between the rheological parameters and the grading parameters of debris flow, [PERSON] reversed-calculated its rheological characteristics, inferred the rheological curve, and established a dynamic equation, uncovering the particle effects of debris flow rheological characteristics [19].  
In summary, the existing studies indicate that the solid content and composition of debris flow slurries are the main factors affecting their rheological relationships. This paper, therefore, employs the state-of-the-art [PERSON] intelligent high-speed rheometer to explore the relationship between shear rate and shear stress of debris flow slurries at different solid volume concentrations and discusses the evolution of rheological parameters with changes in solid volume concentration, aiming to provide practical reference for a deeper understanding of debris flow movement laws and for effective disaster prevention and control.