# Experimental Investigation into the Number of Phases in Debris Flows
## 3 Tested Clastic Materials  
For each of the two debris-flow deposits, three clastic materials with maximum grain diameters (\(d_{\rm max}\)) of 2, 10, and 30 mm were prepared by sieving the large bulk samples up to 100 mm in diameter stored in the laboratory (which were collected during the sampling campaigns carried out at the DYG in November 2015 and November 2019 and JJG in March 2017, respectively ([PERSON] et al. (2024) [45])). The grain-size distributions of six materials, determined using wet sieving coupled with laser granulometry (for \(<\)0.025 mm fraction) (using a laser particle-size analyzer, Beckman Coulter(r)LS 13320) (Beckman Coulter, Brea, CA, USA), are shown in Figure 1.  
\(C_{\rm u}\) and \(C_{\rm c}\) show that both tested materials are very poorly to extremely poorly sorted and are typical of debris-flow deposits [2; 9; 20; 33; 69; 70; 71]. The distinction in particle size distribution (characterized by \(C_{\rm u}\) and \(C_{\rm c}\)) between the DYG and JJG clasts of the same \(d_{\rm max}\) is also obvious; the former shows a more continuous gradation than the latter.  
Furthermore, the materials from the two sites differed significantly in terms of debris geometry. The eight size fractions (ranging from 30 mm to 0.05 mm) of the DYG debris consisted mainly of equidimensional clasts (Figure 2a-h) derived from granite, schist, genesis, and monocrystalline quartz. Platy/flaky clasts of muscovite and biotite that could be identified using megascopic methods (Figure 2d-f) or through a scanning electron microscopy (SEM) (Figure 2h) were frequently observed in relatively fine-grained particles. Perhaps due to the limitations of the adopted separation method, the \(<\)0.005 mm fraction of the DYG deposit was limited almost entirely to platy/flaky detrital mica, with occasional equidimensional grains (Figure 2i).  
Figure 1: Grain-size curves of six clastic materials up to 30 mm in diameter (\(d_{\text{max}}\)), separated from the DYG and JJG debris-flow deposits. \(d_{\text{10}}\) and \(d_{\text{50}}\) are effective grain size and average grain size, respectively. \(\text{C}_{\text{u}}\) and \(\text{C}_{\text{c}}\) are coefficient of uniformity and coefficient of curvature, respectively [21]. \(\rho_{\text{s}}\) is solid density (grain density) (g/cm\({}^{3}\)), which is determined using the methods described in GB/T 50123-2019 [72].  
Figure 2: Distinct shapes of the tested DYG ((**a**–**i**), equidimensional) and JG ((**a**\({}^{\prime}\)**–**i**\({}^{\prime}\)), platy/flaky) debris (eight size fractions of >0.05 mm), and their platy/flaky fines (<0.005 mm fraction). Ec, equidimensional clasts. \(\text{P}_{\text{c}}\), platy clasts (mica). Dq, detrital quartz.  
In contrast, the platy/flaky clasts dominated the JJG debris. The 30-0.05 mm fraction of the JJG debris was composed almost exclusively of platy/flaky or lenticular clasts of slate (Figure 2a\({}^{\prime}\)-h\({}^{\prime}\)), and equidimensional grains (quartz) were infrequently observed (Figure 2e\({}^{\prime}\),\({}^{\prime}\)). The platy/flaky detrital mineral (illite) comprises nearly the entire \(<\)0.005 mm fraction of this material (Figure 2i\({}^{\prime}\)).  
The striking contrast between the grain geometries of the DYG and JJG debris can be ascribed to the aforementioned differences in the bedrock lithologies underlying the two basins.  
In short, the DYG debris is dominated by equidimensional clasts and has continuous gradation, whereas the JJG debris consists of platy/flaky clasts with less continuous gradation.  
In summary, the DYG and JJG flows represent two common debris-flow types: sandy and muddy [4; 29], respectively. Their debris is dominated by equidimensional and platy/flaky clasts, which typify the two end-members of the geometry of clasts [21] that compose debris flows. The experimental results obtained for these two deposits are representative of other debris flows.