## 3 Results
### Rheological Properties and Possible Implications for Debris Flow Modeling  
The rheological parameters are essential for examining debris flow propagation and designing measures for future catastrophic events. For many cases in debris flow simulation, the value of the yield stress is fixed during the flow as a first approximation to understand post-failure characteristics. In this case, the determination of yield stress is crucial. Engineers could obtain the shear strength from field vane tests under in situ conditions and fall cone tests in the laboratory as a priority, which would be more reliable for debris flow initiation. For fine-grained sediments, the yield stress obtained from the material, which is assumed to behave as a Bingham fluid, is very close to the undrained shear strength determined by fall cone tests. For a given sand-rich material, the Bingham yield stress and undrained shear strength were compared for a given solid volume concentration ranging from 50% to 65%. Figure 6 presents a comparison of the shear strength measured from the Bingham yield stress in flow curve tests, the static yield stress in time-dependent tests, and the undrained shear strength in fall cone tests. A simple relationship can be expressed as C\({}_{\text{vs}}\) = 74-S\({}_{\text{u}}\)\({}^{0.1}\) (kPa). For C\({}_{\text{vs}}\) = 50%, the Bingham yield stress and undrained shear strength range between 0.02 and 0.06 kPa (mean value of 40 Pa);  
Figure 5: Static and dynamic rheological properties of sand-rich mine tailings: (**a**) Peak, residual shear stress, and the Bingham yield stresses; (**b**) final viscosity and the Bingham viscosity.  
however, the static yield stress is approximately 0.6-0.9 kPa (mean value of 700 Pa). The difference is more than 10-fold. More interestingly, as described above, the sediments are much more resistant to flow when the shear rate is increased. These results suggest that more research is needed to understand the mechanism related to the high mobilization of debris flows, e.g., entrainment, hydroplaning, yield stress reduction, and wetting processes in debris flow motion. It is necessary to revisit the research work ([24] see Figure 8 in the paper) on failure and post-failure characteristics of mine deposit areas and to estimate the debris flow mobility for such areas. Using the same geometry for the initial slope and volume with different yield stresses, the debris flow propagation can be simply compared. For a given yield stress of 50 Pa, the runout distance is approximately 700 m, but for a stress of 700 Pa, the distance is approximately 100 m. The difference is more than 7-fold. The debris flow velocity is more sensitive to the variation in yield stress. The difference is more than 10-fold. This result means that the debris flow impact can be determined by determining the yield stress. In this context, more precise computational techniques based on rheological studies are required to avoid overdesigning for future disasters and to establish reasonable measures.  
It is very difficult to describe debris flow with one fixed rheological model, because it is expected that the flow behaviors of real debris flow are too complex. In particular, the influence of material parameters (such as the particle size distribution, change in water content, porosity, roughness, edge and wall slip effects) in estimating the flow mobility should be scrutinized in future work. Even with a very simplified hypothesis in which many parameters, such as the particle size distribution, water content, porosity, roughness, solid concentration, and topographic characteristics are simplified with ordinary constants, the research findings presented in this study can be simply applied to debris flow mitigation in mine tailing. In addition, micro-structural evolution of the particles in terms of landslide mobilization has a substantial contribution in the destructuration-restruc