# Experimental Investigation into the Number of Phases in Debris Flows
## 6 Discussion
### Transported Objects by Debris Flows  
In light of the above discussion, debris flows are the flows of the fluids composed of water and sediment, similar to Bingham fluids. Clasts (solids) of any size in the continuous grain-size spectrum of the sediment comprising a debris flow, up to large boulders, are components of the flow (i.e., the fluid).  
Debris-flow sediments are characteristically very poorly to extremely poorly sorted [9; 103; 104], i.e., well graded [12; 96; 21], which means that everything in debris flows is acting as the \"fluid\" [27]. In other words, the coarsest grains in debris flows (whose diameters are expressed here by \(D_{\text{max}}\)) can be as large as tens of centimeters, or even meter-sized, as long as no significant size discontinuities occur between them and other granular components finer than them [77].  
Occurring as a fluid, one-phase debris flows can propagate alone and also function as a transporting medium by carrying larger clasts of \(>>\)\(D_{\text{max}}\). These unusually large (outsized) clasts (boulders or blocks [20; 69; 105]) are objects transported by debris flows rather than components of the flows (Figure 1 in [PERSON] and [PERSON] (1976) [77]; Photo 1 in [PERSON] et al. (1983) [59]; Figure 8.17 in [PERSON] and [PERSON] (1984) [20]; Figure 10 in [PERSON] et al. (2000) [106]; Figure 11).  
As discussed above, the results of the investigations of the relative motion of fluid (water) and solids and bulk behavior suggest that debris flows are much more similar to continuous, homogeneous, isotropic, and monophasic (CHIMP) flows than two-phase hyperconcentrated flows.  
It is well known that rock masses are largely discontinuous, anisotropic, inhomogeneous, and non-elastic [36; 42; 107; 108; 109], but may be considered to be continuous, homogeneous, isotropic, and linearly elastic [110; 111], which greatly simplifies complex rock mass behavior. In contrast, real debris flows themselves are close to CHIMP, and the  
Figure 11: The Dongyuege (DYG) debris-flow deposit and unusually large blocks transported by the flow, showing the constituent sediment of one-phase debris flows acting as transporting medium and outsized blocks serving as transported objects by the flows. (**a**,**\({}^{\prime}\)**) A cross-section of the well-preserved remnant temporary dam (27\({}^{\circ}\)38\({}^{\prime}\)21.53\({}^{\prime\prime}\) N, 98\({}^{\circ}\)44\({}^{\prime}\)4.71\({}^{\prime\prime}\) E) 0.5 km upstream of the fan apex, which was excavated during the sampling campaign on 6–12 November 2019. An outsized boulder with a maximum dimension of approximately 2 m (object transported by the flow) is submerged in the debris-flow diametcion composed of clasts with diameters of approximately \(<\)50 cm (the debris-flow deposit). The view is toward the left bank of the DYG Creek. The man is for scale. Photo by [PERSON]. (**b**,**\({}^{\prime}\)**) The DYG alluvial fan, nine months after the occurrence of the catastrophic debris-flow event. A temporary road was constructed through the debris-flow deposit to look for the people buried by the deposit. The labeled outsized boulders with diameters of up to 9 m from the upstream channel are transported objects contrasted with debris-flow sediments acting as transporting medium. The view is toward the mouth of DYG Creek. The man on the road is for scale. Photo by [PERSON].  
two-phase hypothesis (approach) largely complicates debris flow problems. Most importantly, this could lead to confusion between peculiar (fascinating or surprising) debris-flow phenomena [4; 20; 112] and the relatively more common hyperconcentrated flow processes in mountain catchments. This directly affects the understanding, identification, assessment, and design of mitigation measures of debris flows.