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Enhanced mobility of polydisperse granular flows in a small flume

Enhanced mobility of polydisperse granular flows in a small flume Background: A series of laboratory tests was conducted to investigate the influence of the interaction between coarse and fine particles on the mobility of granular flows in a small flume. Methods: The angle of the upper slope was fixed at 45°, and the lower slope was inclined at angles of 0°, 5°, 10°, and 15° in different cases. Three monodisperse materials (gravel, coarse sand, and fine sand) were mixed, and the proportion of each material in each test was varied but maintained the same total mass of 3.0 kg. Results: Test results show that the proportion of fine sand strongly influenced the run-out of polydisperse materials. With increasing proportion of fine sand, the run-outs of granular flows increased until its peak. However, the run-outs decreased with further more fine sand. Discussion: The reason might be that a thin layer of fine sand acted as rollers for the rolling of the gravel, leading to the reduction of effective friction resistance during the movement; when excessive amount of fine sand was involved, these rollers were thrown into disarray so that the particles were either blocked or forced into sliding. Conclusion: This implies that an appropriate proportion of fine particles were partly responsible for the long run-out of rock avalanches. Keywords: Polydisperse granular flow; Run-out; Deposit morphology; Flume test Background The physical behavior of dense granular flows has Granular flows are widespread in nature as rockslides, attracted considerable attention from laboratory experiment volcanic block-and-ash pyroclastic flows, and dry rock and numerical modeling points of view. The dynamics of and debris avalanches. An important feature of these the collapses of axisymmetric and two-dimensional granular flows is their extremely high mobility (up to tens of kilo- columns onto a horizontal surface and the subsequent meters), which is capable of moving freely from their granular propagation have been investigated experimentally sources. Many researchers (e.g. Davies et al. 2012; Heim, (e.g. Balmforth and Kerswell, 2005; Lajeunesse et al., 2005; 1932; Hsü, 1975; Scheidegger, 1973) reported that the Lube et al., 2005). The test results challenged the traditional mobility of these flows is dependent on their volume, view that the run-out depends only on the volume of the indicating that large events travel farther than smaller materials involved, and emphasized the importance of the ones. However, the long run-out granular flows moved initial aspect ratio of the column instead. Other researchers far beyond the distance that could have been expected presented some numerical simulations to reproduce natural when considering the size effect alone (Erismann and mass flows over complex terrains (e.g. Denlinger and Abele, 2001). The fundamental understanding of the Iverson, 2004; Iverson and Denlinger, 2001; Pudasaini propagation mechanisms of granular flows is important, and Hutter, 2003) and experimental flows (e.g. Pudasaini in particular when geomorphological circumstances and et al., 2008; Yang et al., 2014). Parameters used in the mechanical properties of involved materials are varied numerical simulations are usually obtained by back ana- according to different specific events. lyses of occurred events or by calibration, as a result of the extreme complexity of such phenomena and the still * Correspondence: szmiyqq@163.com incomplete knowledge of the governing laws controlling Chinese Academy of Sciences, Institute of Mountain Hazards and Environment, Chengdu 610041, China the behavior of these materials (Crosta et al., 2009). Full list of author information is available at the end of the article © 2015 Yang et al.; licensee BioMed Central. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. Yang et al. Geoenvironmental Disasters (2015) 2:12 Page 2 of 9 Experiment plays a significant role in contributing a that of larger ones. They concluded that the mobility is better understanding of propagation mechanisms and modified when the mixture of different-sized particles was factors influencing velocity and deposit characteristics used, especially with 30% fine particles in mass proportion. (Yang et al., 2011). A majority of previous experiments Phillips et al. (2006) presented laboratory measurements have focused on the case of monodisperse materials of flows of binary mixtures of fine and coarse granular ma- down inclined roughened slope (e.g. Davies et al. 1999; terials, and showed that the interaction between them can Manzella and Labiouse, 2013; Pouliquen, 1999). How- result in significantly increased mobility. They used heur- ever, particles rarely have a regular shape or a uniform istic models to illustrate that some mechanisms are likely size distribution (Gray and Ancey, 2011). Research ac- to occur in granular flows containing a wide range of grain counting for interactions among constitute particles with sizes. Degaetano et al. (2013) investigated experimentally different grain sizes and shapes on the mobility of granu- the run-out resulting from the collapse of a granular col- lar flows is still out of reach. Some researchers have umn containing two particle species that differ in size reported that experimental granular flows containing a only. They found a clear dependence of run-out on both range of particle sizes can exhibit macro-scale properties initial mixture arrangement and proportion. that differ from flows containing a single particle size In this work, the run-out and deposition height of poly- (Goujon et al., 2007; Moro et al., 2010; Phillips et al., 2006; disperse materials moving over a rough inclined flume Roche et al.,2006). The variety of mechanical properties were investigated by conducting a series of laboratory can lead to a diversity and complication of behavior due experiments, and the effect of the interactions between to the interaction of polydisperse components. Actually, polydisperse components on the mobility of the granular natural flows generally contain particles of a fairly wide flows was examined. These granular flows contained a range of sizes; in some cases, the size range of particles range of particle sizes from 0.1 mm to 10 mm, which was can vary from tens of micrometers up to the order of a a rather narrow range compared to those materials meter (Roche et al., 2006). Fragmentation is a prominent involved in geophysical granular flows. Determining the process in the emplacement of field rock avalanches, and chief interactions with a wide size distribution is difficult, can cause materials extensively fractured/shattered (e.g. and the choice of the particle sizes in this study aided the Blasio and Crosta, 2014; Crosta et al., 2007; Davies and understanding of complex particle interactions between McSaveney, 2009). Therefore considering a wide range of coarse and fine particles in real events. particle gradation is important for proper understanding of natural granular flow. Experiments and methods Roche et al. (2006) performed experiments on a column Experimental set-up of fluidized particles that were released into an enclosed The two-part flume used in the tests consisted of two channel, and the behavior of fine particles is distinct from slopes with the upper and lower slope (Figure 1). Each Figure 1 Experimental set-up. Yang et al. Geoenvironmental Disasters (2015) 2:12 Page 3 of 9 slope was 1.5 m in length. The two slopes were con- nected by hinges that permit inclination adjustments. The angle of the upper slope was fixed at 45°, and the lower slope was inclined at angles of 0°, 5°, 10°, and 15°. The width of the flume was 0.18 m, which was sufficiently small for the flows to be one-dimensional; it was also sufficiently large for negligible side wall effects. A gate, perpendicular to the upper slope, can be lifted manually (but rapidly). Employed materials Polydisperse materials were composed of three monodis- perse materials in varying proportions but always main- tained the same total mass of 3.0 kg. The bulk density of the three monodisperse materials was about 2.6 g/cm , and thus the total volume of the polydisperse materials used in each test remained nearly the same. The three monodisperse materials (Figure 2) were: a) Gravel: coarse particles; the grain size is 4.75 ~ 9.5 mm; b) Coarse sand: fine particles; grain size is 0.42 ~ 2.0 mm; c) Fine sand: Toyoura sand, which is a very fine material. The grain size is 0.1 ~ 0.3 mm. Data acquisition Each test was filmed by a video camera. The run-out and deposition height were measured manually after each test. The deposit was divided into two parts based on the accumulation of particles (Figure 3). The first part, i.e. the main part of the deposit, represented the coherent main mass of the deposit. The second part, which was only a single layer, was discontinuous from the first part and easy to distinguish. The measurements (run-out, deposition height, weight) were conducted by taking into account only the main part of the deposit. Individual particles moved beyond the flume (the rest) were not considered in this study. In the literature, the Figure 2 Granular materials used: a) Gravel; b) Coarse sand; run-out is commonly defined as the total horizontal c) Fine sand. travel distance from the top of the breakaway scar to the distal end of the deposit, or the horizontal distance travelled by the center of moving mass. In this work, The main part of the deposit The second part of the deposit Figure 3 The measurement of the deposit. Yang et al. Geoenvironmental Disasters (2015) 2:12 Page 4 of 9 the run-out was the length of the main part of the deposit accumulated on the lower slope. This choice On the 0° slope facilitated homogeneous results that were easy to compare. The deposition height of the main part, perpendicular to the lower slope, was measured at 10 cm interval along the Fine sand midstream path of the lower slope. Coarse sand 88 cases were studied. The inclination of the lower Gravel slope (0°, 5°, 10°, and 15°) and the proportion of each material (gravel, coarse sand, and fine sand) were varied. Each case was repeated at least three times to evaluate the repeatability and assess the validity of the corre- sponding measurements. After the test, each part (i.e. the main part of the deposit, the second part of the de- posit, and the rest) of the deposit was weighed respect- 0 102030405060 ively, and their total mass was added. The loss of Run-out [cm] particles was estimated to be less than 1 g. Figure 5 Deposit morphologies of the main part of the deposit for the three monodisperse materials on the 0° slope. Experimental results Monodisperse material The run-outs of the monodisperse materials increased coarser the particles, the more particles accumulated on the with the inclination of the lower slope (Figure 4). It is easy second part of the deposit (Figure 9). This means that coarse to understand that the materials had a higher mobility on particles were easier to travel a long distance. The mass of the steeper slopes. However, it is surprising that the run-outs fine sand accumulated on the second part of the deposit was of the three monodisperse materials were almost identical 1.0 g regardless of the inclination of the lower slope. With the on the slope with the same inclination. Coarse materials increasing angle of the lower slope, more coarse sand and would move farther than fine materials due to less energy gravel moved far and deposited on the second part, especially consumption caused by intergranular friction. for the gravel. This implies that coarse particles were prone to The morphology of the main part of the deposit for the travel farther than fine particles on the steep slope. threemonodispersematerials on theslope of 0°,5°, 10°, and 15° are shown in Figure 5, 6, 7 and 8, respectively. The de- A polydisperse material with the same mass of gravel, posit morphology of the three monodisperse materials coarse sand, and fine sand was similar on the slope with the same inclination. A polydisperse material was used, which consisted of The mass of each material (i.e. gravel, coarse sand, and fine 1.0 kg gravel (M = 1.0 kg), 1.0 kg coarse sand (M = g c sand) into the second part of the deposit was weighed. The 1.0 kg), and 1.0 kg fine sand (M = 1.0 kg). The run-out of this polydisperse material is shown in Figure 10, combined Gravel Coarse sand On the 5° slope Fine sand Fine sand Coarse sand Gravel 05 10 15 Angle of the lower slope [˚] 0 102030405060 Run-out [cm] Figure 4 Run-out of the main part of the deposit for the three monodisperse materials on the slopes with different inclinations. Figure 6 Deposit morphologies of the main part of the deposit The error bars show standard error of the average run-out for each test. for the three monodisperse materials on the 5° slope. Run-out [cm] Deposition height [mm] Deposition height [mm] Yang et al. Geoenvironmental Disasters (2015) 2:12 Page 5 of 9 80 300 On the 10° slope Fine sand Coarse sand Fine sand Gravel Coarse sand Gravel 05 10 15 010 20 30 40 50 60 Run-out [cm] Angle of the lower slope [˚] Figure 9 Mass of the materials accumulated on the second part Figure 7 Deposit morphologies of the main part of the deposit of the deposit. for the three monodisperse materials on the 10° slope. with those of the three monodisperse materials. The mo- Polydisperse materials with various fractions of fine sand bility of the polydisperse material was significantly In order to further confirm the effect of the interactions higher than the monodisperse materials. This implies between particles on enhancing the mobility of granular that the interactions between coarse and fine particles flows, polydisperse materials with various fractions of were helpful to enhance the mobility of granular flows. fine sand were released. In each series, the mass of the Figure 11 shows the deposit morphology of this poly- gravel was maintained (1.0 kg, 1.4 kg, or 1.8 kg), and the disperse material (M =M =M = 1.0 kg) on the 0°, 5°, rest consisted of coarse sand and fine sand at different g c f 10°, and 15° slope, respectively. Comparing with the mixing proportions. Fine sand mass fraction F was monodisperse materials, the deposit shape of this poly- defined as the proportion of fine sand in total mass. For disperse material was low and long. example, when the mass of the gravel was 1.0 kg, the Each case was repeated three times with this polydis- mass of the fine sand was 0, 0.4 kg, 0.8 kg, 1.2 kg, perse material (M =M =M = 1.0 kg), and the second 1.6 kg, and 2.0 kg, respectively. Thus, F ranged from 0 g c f f part of the deposit were weighted for each time (Figure 12). (no fine sand) to 0.67 (all fine sand) when the mass of Less than 100 g of the materials accumulated on the the gravel was 1.0 kg. second part of the deposit, and a majority of particles travelled a long distance. Gravel Coarse sand Fine sand On the 15° slope Composite Fine sand 60 Coarse sand Gravel 20 20 0 5 10 15 Angle of the lower slope [˚] Figure 10 Run-out of the main part of the deposit for the 0 102030405060 polydisperse material (M =M =M = 1.0 kg) on different slopes, g c f Run-out [cm] comparing with the run-outs for the three monodisperse Figure 8 Deposit morphologies of the main part of the deposit materials. The error bars show standard error of the average run-out for the three monodisperse materials on the 15° slope. for each test. Deposition height [mm] Deposition height [mm] Mass of the second part of the Run-out [cm] deposit [g] Yang et al. Geoenvironmental Disasters (2015) 2:12 Page 6 of 9 was involved. These rollers threw into disarray so that the particles might be either blocked or forced into sliding. 0° Furthermore, from the point of view of energy, the energy 5° was consumed significantly due to interegranular friction 10° when excessive amount of fine sand was involved that the 15° gravel was embedded in a matrix of fine sand. When F was small (0 < F ≤0.2), the flows with 1.8 kg f f gravel (blue line, Figure 13) exhibited the highest mobil- ity. This implies that the polydisperse material contain- ing more coarse particles might travel farther than that with less coarse particles at small F . The main cause may be that the gravel typically had a high porosity, and the interactions between particles would be reduced by 020 40 60 80 100 120 substituting a coarse particle for the same mass of fine Run-out [cm] particles. Frictional loss was proportional to the surface area of particles available for the interactions, and thus Figure 11 Deposit morphology of the main part of the deposit for the polydisperse material (M =M =M = 1.0 kg) on the less energy was consumed by intergranular friction when g c f different slopes. the mass of the gravel increased. The flow with 1.8 kg gravel at F = 0.13 (1.8 kg gravel, Figure 13 shows the run-outs of flows on the 15° slope, 0.8 kg coarse sand, and 0.4 kg fine sand) travelled the which were consisting of coarse and fine particles: gravel longest run-out of 109 cm; the maximum run-out of as coarse particle, and coarse and fine sand as fine 102 cm was observed for the flow with 1.4 kg gravel at particle. The mobility was enhanced due to the interac- F = 0.27 (1.4 kg gravel, 0.8 kg coarse sand, and 0.8 kg tions between particles on the 15° slope, except in the fine sand), and the peak in run-out was 98.3 cm for the case with 1.0 kg gravel and 2.0 kg fine sand where the flow with 1.0 kg grave at F = 0.27 (1.0 kg gravel, 1.2 kg run-out of this polydisperse material was significantly coarse sand, and 0.8 kg fine sand). For the polydisperse smaller than that of the three monodisperse materials. materials with different mass of gravel, the flows exhib- The trend of run-outs for the polydisperse materials in ited the highest mobility at different F . The interaction the three series was similar. The run-outs increased with of particles with different sizes and shapes became more F until reaching a peak, and then decreased with further complicated when internal structure of granular flows increasing F . This suggests that a certain amount of fine was varied. The precise details of interactions among sand advanced the mobility of granular flows, and exces- constituent particles are still poorly understood. sive amount of fine sand obstructed their propagation. The flows containing 1.8 kg gravel show a peak in The reason might be that a thin layer of fine sand acted run-out over a range of F between 0.1 and 0.2. The peak as rollers for the rolling of the gravel, leading to the re- in run-out extended over a greater range of F between duction of effective friction resistance during the move- 0.1 and 0.3 for the flows containing 1.4 kg gravel, and of ment; the interactions between particles became more F between 0.1 and 0.4 for the flows containing 1.0 kg complicated than they just acted as a single-row roller to gravel. The peak was sharper in the experiments with lubricate the gravel when excessive amount of fine sand 1.8 kg gravel. This suggests that the mobility was more 3.0% 2.6%2.6% first time second time third time 2.5% 1.9% 2.0% 1.8% 1.6% 1.5% 1.5% 1.5% 1.5% 1.2% 1.1% 1.0% 1.0% 0.8% 0.5% 0.0% 0 5 10 15 Angle of the lower slope [˚] Figure 12 Mass of the second part of the deposit for the polydisperse material (M =M =M = 1.0 kg) over three runs on g c f different slopes. Deposition height [mm] Mass percentage of the second part of the deposit [g] Yang et al. Geoenvironmental Disasters (2015) 2:12 Page 7 of 9 120 120 Mg=1.0 kg Mg=1.0 kg 100 Mg=1.4 kg 100 Mg=1.4 kg Mg=1.8 kg Mg=1.8 kg On the 5° slope On the 15° slope 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Fine sand mass fraction Fine sand mass fraction Figure 15 Run-outs of the main part of the deposit for the Figure 13 Run-outs of the main part of the deposit for the polydisperse materials with various fractions of fine sand on polydisperse materials with various fractions of fine sand on the 5° slope. The error bars show standard error of the average the 15° slope. The error bars show standard error of the average run-out for each test. run-out for each test. sensitive to the proportion of fine sand when more coarse and fine particles on enhancing the mobility of gravel was involved. polydisperse materials was not fully developed on the The run-outs of flows on the slope of 10°, 5°, and 0° gentle slopes, i.e. the rolling motion did not readily are shown in Figures 14, 15, and 16, respectively. The occur on the gentle slopes. On the 5° and 0° slope, the polydisperse materials also travelled farther than the run-outs were almost identical at large F (0.3 ~ 0.67) three monodisperse materials on these slopes. The regardless of the mass of gravel. This was because the trends of run-outs were similar to that on the 15° slope. gravel embedded in a matrix of fine sand and was diffi- However, the run-outs on the gentle slopes were shorter cult to move on these gentle slopes. than that on the 15° slope. This indicates that the in- Figure 17 shows the deposit morphology of the main clination of the lower slope significantly influenced the part of the deposit accumulated on the lower slope with mobility of polydisperse materials. The difference in different inclinations. The three flows, consisted of vari- run-out was not significant for a range of F on these ous constitute particles, were selected for comparison. gentle slopes, comparing with that on the 15° slope. Each of the three flows (M = 1.0 kg, M = 1.2 kg, M = g c f This implies that the effect of the interactions between 0.8 kg; M = 1.4 kg, M = 0.8 kg, M = 0.8 kg; M = 1.8 kg, g c f g 120 120 Mg=1.0 kg Mg=1.0 kg 100 100 Mg=1.4 kg Mg=1.4 kg Mg=1.8 kg Mg=1.8 kg 80 80 60 60 40 40 On the 0° slope On the 10° slope 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Fine sand mass fraction Fine sand mass fraction Figure 14 Run-outs of the main part of the deposit for the Figure 16 Run-outs of the main part of the deposit for the polydisperse materials with various fractions of fine sand on polydisperse materials with various fractions of fine sand on the 10° slope. The error bars show standard error of the average the 0° slope. The error bars show standard error of the average run-out for each test. run-out for each test. Run-out [cm] Run-out [cm] Run-out [cm] Run-out [cm] Yang et al. Geoenvironmental Disasters (2015) 2:12 Page 8 of 9 morphology of granular flows was also influenced strongly by the inclination of the lower slope. The deposit profile a) Mg=1.8 kg; Mc=0.8 kg; Mf=0.4 kg was much flatter and longer on the steep slopes (15° and 10°) than that on the gentle slopes (5° and 0°). This 15˚ phenomenon implies that there was a critical inclination 25 10˚ of the lower slope between 5° and 10° at which particle 5˚ motion in flows changed in this work. When the slope was steeper than the critical inclination, the particles 0˚ were prone to rolling. Otherwise, the particles exhibited sliding motion. For all polydisperse materials used in the experiments, the deposits exhibited some common features as follows. First, coarse particles segregated to the surface of fine 0 20406080 100 120 particles. This phenomenon is also observed frequently Run-out [cm] in field investigations. Second, the region of maximum concentration of particles was farther from the flow origin on the steeper slope, that is, more materials were b) Mg=1.4 kg; Mc=0.8 kg; Mf=0.8 kg transported a long distance. A broad range of granular materials accumulated from the position 20 cm to 15˚ 90 cm on the 15° and 10° slopes. On the gentle slopes, 10˚ however, the deposits concentrated a narrow range from the position 0 cm to the position 40 cm. The materials 20 5˚ were prone to contribute to add the deposition height 0˚ rather than the run-out on the gentle slope. Finally, the deposit morphologies were almost similar on the same slope for the three flows with different polydisperse components. This implies that the mobility of granular flows was more sensitive to the inclination of the lower 0 20 40 60 80 100 120 slope than granular component. Run-out [cm] Method The flows described in this study varied the proportion c) Mg=1.0 kg; Mc=1.2 kg; Mf=0.8 kg 35 of constitute particles but maintained the same total mass to examine the effect of interactions between parti- 15˚ cles on the mobility of granular flows. 10˚ Results 5˚ Test results indicate that the run-outs of the flows with 0˚ a wide range of grain sizes were larger than the flows only containing mono-sized particles. The proportion of fine sand strongly influenced the run-out of the polydis- perse materials. The fine sand was transported with the gravel, and 0 20406080 100 120 naturally segregated to the base of the flow under grav- ity. The rolling of fine sand acted as a lubricant for the Run-out [cm] gravel by the interactions with each other, and thus the Figure 17 Deposit morphology of the main part of the deposit friction resistance reduced during the movement. With accumulated on the lower slope with different inclinations: a) M = 1.8 kg; M = 0.8 kg; M = 0.4 kg; b) M = 1.4 kg; M = g c f g c increasing F , a greater proportion of gravel was com- 0.8 kg; M = 0.8 kg; c) M = 1.0 kg; M = 1.2 kg; M = 0.8 kg. f g c f pletely supported by the fine sand, and the run-out reached its peak. This indicates that rolling motion was M = 0.8 kg, M = 0.4 kg) typically exhibited the longest very important in flow propagation, and increasing c f run-out in the series on the 15° slope. The deposit proportion of rolling to sliding in particle motion re- morphologies on the steep and gentle slopes significantly duced energy consumption. However, the run-out de- departed from each other. This indicates that the deposit creased with further increasing F . This was because Deposition height [mm] Deposition height [mm] Deposition height [mm] Yang et al. Geoenvironmental Disasters (2015) 2:12 Page 9 of 9 intergranular friction dominated which was the primary of Mountain Hazards and Environment, Chengdu 610041, China. Department of Environmental Engineering Science, Gunma University, Kiryu source of energy loss, and thus limited the propagation 376-8515, Japan. of granular flows. The deposit characteristics on the steep and gentle Received: 11 October 2014 Accepted: 25 February 2015 slopes significantly departed from each other. The deposit profile was much flatter and longer on the steep slopes References (15° and 10°) than that on the gentle slopes (5° and 0°). Balmforth NJ, Kerswell RR (2005) Granular collapse in two dimensions. J Fluid Mech 538:399–428 The region of maximum concentration of particles was Blasio FVD, Crosta G (2014). Simple physical model for the fragmentation of rock farther from the flow origin on the steeper slope, i.e., avalanches. 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Phillips JC, Hogg AJ, Kerswell RR, Thomas NH (2006) Enhanced mobility of granular mixtures of fine and coarse particles. Earth Planet Sci Lett 246:466–480 Competing interests Pouliquen O (1999) Scaling laws in granular flows down rough inclined planes. The authors declare that they have no competing interests. Phys Fluids 11(3):542 Pudasaini SP, Hutter K (2003) Rapid shear flows of dry granular masses down Authors’ contributions curved and twisted channels. J Fluid Mech 495:193–208 FC and KU laid out the experiment scheme and provided discussions about Pudasaini SP, Wang YQ, Sheng LT, Hsiau SS, Hutter K, Katzenbach R (2008) the test results; QY and ZS conducted the small flume tests; QY and ZS Avalanching granular flows down curved and twisted channels: Theoretical drafted the manuscript; all authors read and approved the final manuscript. and experimental results. Phys Fluids 20:073302 Roche O, Gilbertson MA, Phillips JC, Sparks RSJ (2006) The influence of particle Acknowledgement size on the flow of initially fluidized powders. Power Technology 166:167–174 This work is supported by National Natural Science Foundation of China Scheidegger AE (1973) On the prediction of the reach and velocity of (project No. 41402244), the Fundamental Research Funds for the Central catastrophic landslides. Rock Mech 5:231–236 Universities (project No. A0920502051413-13), and Scientific Research Yang QQ, Cai F, Ugai K, Yamada M, Su ZM, Ahmed A, Huang RQ, Xu Q (2011) Foundation for Returned Scholars, Ministry of Education of China. This Some factors affecting mass-front velocity of rapid dry granular flows in a research is also partly supported by the Chinese State Key Basic Research large flume. Eng Geol 122:249–260 Program (project 2013CB733201). Much gratefulness is extended to the two Yang QQ, Cai F, Su ZM, Ugai K, Xu LY, Huang RQ, Xu Q (2014) Numerical anonymous reviewers and the editors, and their comments strongly contributed Simulation of Granular Flows in a Large Flume Using Discontinuous in improving the quality of this manuscript. Deformation Analysis. Rock Mech Rock Engng 47(6):2299–2306 Author details Faculty of Geosciences and Environmental Engineering, Southwest Jiaotong University, Chengdu 610031, China. Chinese Academy of Sciences, Institute http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Geoenvironmental Disasters Springer Journals

Enhanced mobility of polydisperse granular flows in a small flume

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Environment; Environment, general; Earth Sciences, general; Geography (general); Geoecology/Natural Processes; Natural Hazards; Environmental Science and Engineering
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2197-8670
DOI
10.1186/s40677-015-0019-4
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Abstract

Background: A series of laboratory tests was conducted to investigate the influence of the interaction between coarse and fine particles on the mobility of granular flows in a small flume. Methods: The angle of the upper slope was fixed at 45°, and the lower slope was inclined at angles of 0°, 5°, 10°, and 15° in different cases. Three monodisperse materials (gravel, coarse sand, and fine sand) were mixed, and the proportion of each material in each test was varied but maintained the same total mass of 3.0 kg. Results: Test results show that the proportion of fine sand strongly influenced the run-out of polydisperse materials. With increasing proportion of fine sand, the run-outs of granular flows increased until its peak. However, the run-outs decreased with further more fine sand. Discussion: The reason might be that a thin layer of fine sand acted as rollers for the rolling of the gravel, leading to the reduction of effective friction resistance during the movement; when excessive amount of fine sand was involved, these rollers were thrown into disarray so that the particles were either blocked or forced into sliding. Conclusion: This implies that an appropriate proportion of fine particles were partly responsible for the long run-out of rock avalanches. Keywords: Polydisperse granular flow; Run-out; Deposit morphology; Flume test Background The physical behavior of dense granular flows has Granular flows are widespread in nature as rockslides, attracted considerable attention from laboratory experiment volcanic block-and-ash pyroclastic flows, and dry rock and numerical modeling points of view. The dynamics of and debris avalanches. An important feature of these the collapses of axisymmetric and two-dimensional granular flows is their extremely high mobility (up to tens of kilo- columns onto a horizontal surface and the subsequent meters), which is capable of moving freely from their granular propagation have been investigated experimentally sources. Many researchers (e.g. Davies et al. 2012; Heim, (e.g. Balmforth and Kerswell, 2005; Lajeunesse et al., 2005; 1932; Hsü, 1975; Scheidegger, 1973) reported that the Lube et al., 2005). The test results challenged the traditional mobility of these flows is dependent on their volume, view that the run-out depends only on the volume of the indicating that large events travel farther than smaller materials involved, and emphasized the importance of the ones. However, the long run-out granular flows moved initial aspect ratio of the column instead. Other researchers far beyond the distance that could have been expected presented some numerical simulations to reproduce natural when considering the size effect alone (Erismann and mass flows over complex terrains (e.g. Denlinger and Abele, 2001). The fundamental understanding of the Iverson, 2004; Iverson and Denlinger, 2001; Pudasaini propagation mechanisms of granular flows is important, and Hutter, 2003) and experimental flows (e.g. Pudasaini in particular when geomorphological circumstances and et al., 2008; Yang et al., 2014). Parameters used in the mechanical properties of involved materials are varied numerical simulations are usually obtained by back ana- according to different specific events. lyses of occurred events or by calibration, as a result of the extreme complexity of such phenomena and the still * Correspondence: szmiyqq@163.com incomplete knowledge of the governing laws controlling Chinese Academy of Sciences, Institute of Mountain Hazards and Environment, Chengdu 610041, China the behavior of these materials (Crosta et al., 2009). Full list of author information is available at the end of the article © 2015 Yang et al.; licensee BioMed Central. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly credited. Yang et al. Geoenvironmental Disasters (2015) 2:12 Page 2 of 9 Experiment plays a significant role in contributing a that of larger ones. They concluded that the mobility is better understanding of propagation mechanisms and modified when the mixture of different-sized particles was factors influencing velocity and deposit characteristics used, especially with 30% fine particles in mass proportion. (Yang et al., 2011). A majority of previous experiments Phillips et al. (2006) presented laboratory measurements have focused on the case of monodisperse materials of flows of binary mixtures of fine and coarse granular ma- down inclined roughened slope (e.g. Davies et al. 1999; terials, and showed that the interaction between them can Manzella and Labiouse, 2013; Pouliquen, 1999). How- result in significantly increased mobility. They used heur- ever, particles rarely have a regular shape or a uniform istic models to illustrate that some mechanisms are likely size distribution (Gray and Ancey, 2011). Research ac- to occur in granular flows containing a wide range of grain counting for interactions among constitute particles with sizes. Degaetano et al. (2013) investigated experimentally different grain sizes and shapes on the mobility of granu- the run-out resulting from the collapse of a granular col- lar flows is still out of reach. Some researchers have umn containing two particle species that differ in size reported that experimental granular flows containing a only. They found a clear dependence of run-out on both range of particle sizes can exhibit macro-scale properties initial mixture arrangement and proportion. that differ from flows containing a single particle size In this work, the run-out and deposition height of poly- (Goujon et al., 2007; Moro et al., 2010; Phillips et al., 2006; disperse materials moving over a rough inclined flume Roche et al.,2006). The variety of mechanical properties were investigated by conducting a series of laboratory can lead to a diversity and complication of behavior due experiments, and the effect of the interactions between to the interaction of polydisperse components. Actually, polydisperse components on the mobility of the granular natural flows generally contain particles of a fairly wide flows was examined. These granular flows contained a range of sizes; in some cases, the size range of particles range of particle sizes from 0.1 mm to 10 mm, which was can vary from tens of micrometers up to the order of a a rather narrow range compared to those materials meter (Roche et al., 2006). Fragmentation is a prominent involved in geophysical granular flows. Determining the process in the emplacement of field rock avalanches, and chief interactions with a wide size distribution is difficult, can cause materials extensively fractured/shattered (e.g. and the choice of the particle sizes in this study aided the Blasio and Crosta, 2014; Crosta et al., 2007; Davies and understanding of complex particle interactions between McSaveney, 2009). Therefore considering a wide range of coarse and fine particles in real events. particle gradation is important for proper understanding of natural granular flow. Experiments and methods Roche et al. (2006) performed experiments on a column Experimental set-up of fluidized particles that were released into an enclosed The two-part flume used in the tests consisted of two channel, and the behavior of fine particles is distinct from slopes with the upper and lower slope (Figure 1). Each Figure 1 Experimental set-up. Yang et al. Geoenvironmental Disasters (2015) 2:12 Page 3 of 9 slope was 1.5 m in length. The two slopes were con- nected by hinges that permit inclination adjustments. The angle of the upper slope was fixed at 45°, and the lower slope was inclined at angles of 0°, 5°, 10°, and 15°. The width of the flume was 0.18 m, which was sufficiently small for the flows to be one-dimensional; it was also sufficiently large for negligible side wall effects. A gate, perpendicular to the upper slope, can be lifted manually (but rapidly). Employed materials Polydisperse materials were composed of three monodis- perse materials in varying proportions but always main- tained the same total mass of 3.0 kg. The bulk density of the three monodisperse materials was about 2.6 g/cm , and thus the total volume of the polydisperse materials used in each test remained nearly the same. The three monodisperse materials (Figure 2) were: a) Gravel: coarse particles; the grain size is 4.75 ~ 9.5 mm; b) Coarse sand: fine particles; grain size is 0.42 ~ 2.0 mm; c) Fine sand: Toyoura sand, which is a very fine material. The grain size is 0.1 ~ 0.3 mm. Data acquisition Each test was filmed by a video camera. The run-out and deposition height were measured manually after each test. The deposit was divided into two parts based on the accumulation of particles (Figure 3). The first part, i.e. the main part of the deposit, represented the coherent main mass of the deposit. The second part, which was only a single layer, was discontinuous from the first part and easy to distinguish. The measurements (run-out, deposition height, weight) were conducted by taking into account only the main part of the deposit. Individual particles moved beyond the flume (the rest) were not considered in this study. In the literature, the Figure 2 Granular materials used: a) Gravel; b) Coarse sand; run-out is commonly defined as the total horizontal c) Fine sand. travel distance from the top of the breakaway scar to the distal end of the deposit, or the horizontal distance travelled by the center of moving mass. In this work, The main part of the deposit The second part of the deposit Figure 3 The measurement of the deposit. Yang et al. Geoenvironmental Disasters (2015) 2:12 Page 4 of 9 the run-out was the length of the main part of the deposit accumulated on the lower slope. This choice On the 0° slope facilitated homogeneous results that were easy to compare. The deposition height of the main part, perpendicular to the lower slope, was measured at 10 cm interval along the Fine sand midstream path of the lower slope. Coarse sand 88 cases were studied. The inclination of the lower Gravel slope (0°, 5°, 10°, and 15°) and the proportion of each material (gravel, coarse sand, and fine sand) were varied. Each case was repeated at least three times to evaluate the repeatability and assess the validity of the corre- sponding measurements. After the test, each part (i.e. the main part of the deposit, the second part of the de- posit, and the rest) of the deposit was weighed respect- 0 102030405060 ively, and their total mass was added. The loss of Run-out [cm] particles was estimated to be less than 1 g. Figure 5 Deposit morphologies of the main part of the deposit for the three monodisperse materials on the 0° slope. Experimental results Monodisperse material The run-outs of the monodisperse materials increased coarser the particles, the more particles accumulated on the with the inclination of the lower slope (Figure 4). It is easy second part of the deposit (Figure 9). This means that coarse to understand that the materials had a higher mobility on particles were easier to travel a long distance. The mass of the steeper slopes. However, it is surprising that the run-outs fine sand accumulated on the second part of the deposit was of the three monodisperse materials were almost identical 1.0 g regardless of the inclination of the lower slope. With the on the slope with the same inclination. Coarse materials increasing angle of the lower slope, more coarse sand and would move farther than fine materials due to less energy gravel moved far and deposited on the second part, especially consumption caused by intergranular friction. for the gravel. This implies that coarse particles were prone to The morphology of the main part of the deposit for the travel farther than fine particles on the steep slope. threemonodispersematerials on theslope of 0°,5°, 10°, and 15° are shown in Figure 5, 6, 7 and 8, respectively. The de- A polydisperse material with the same mass of gravel, posit morphology of the three monodisperse materials coarse sand, and fine sand was similar on the slope with the same inclination. A polydisperse material was used, which consisted of The mass of each material (i.e. gravel, coarse sand, and fine 1.0 kg gravel (M = 1.0 kg), 1.0 kg coarse sand (M = g c sand) into the second part of the deposit was weighed. The 1.0 kg), and 1.0 kg fine sand (M = 1.0 kg). The run-out of this polydisperse material is shown in Figure 10, combined Gravel Coarse sand On the 5° slope Fine sand Fine sand Coarse sand Gravel 05 10 15 Angle of the lower slope [˚] 0 102030405060 Run-out [cm] Figure 4 Run-out of the main part of the deposit for the three monodisperse materials on the slopes with different inclinations. Figure 6 Deposit morphologies of the main part of the deposit The error bars show standard error of the average run-out for each test. for the three monodisperse materials on the 5° slope. Run-out [cm] Deposition height [mm] Deposition height [mm] Yang et al. Geoenvironmental Disasters (2015) 2:12 Page 5 of 9 80 300 On the 10° slope Fine sand Coarse sand Fine sand Gravel Coarse sand Gravel 05 10 15 010 20 30 40 50 60 Run-out [cm] Angle of the lower slope [˚] Figure 9 Mass of the materials accumulated on the second part Figure 7 Deposit morphologies of the main part of the deposit of the deposit. for the three monodisperse materials on the 10° slope. with those of the three monodisperse materials. The mo- Polydisperse materials with various fractions of fine sand bility of the polydisperse material was significantly In order to further confirm the effect of the interactions higher than the monodisperse materials. This implies between particles on enhancing the mobility of granular that the interactions between coarse and fine particles flows, polydisperse materials with various fractions of were helpful to enhance the mobility of granular flows. fine sand were released. In each series, the mass of the Figure 11 shows the deposit morphology of this poly- gravel was maintained (1.0 kg, 1.4 kg, or 1.8 kg), and the disperse material (M =M =M = 1.0 kg) on the 0°, 5°, rest consisted of coarse sand and fine sand at different g c f 10°, and 15° slope, respectively. Comparing with the mixing proportions. Fine sand mass fraction F was monodisperse materials, the deposit shape of this poly- defined as the proportion of fine sand in total mass. For disperse material was low and long. example, when the mass of the gravel was 1.0 kg, the Each case was repeated three times with this polydis- mass of the fine sand was 0, 0.4 kg, 0.8 kg, 1.2 kg, perse material (M =M =M = 1.0 kg), and the second 1.6 kg, and 2.0 kg, respectively. Thus, F ranged from 0 g c f f part of the deposit were weighted for each time (Figure 12). (no fine sand) to 0.67 (all fine sand) when the mass of Less than 100 g of the materials accumulated on the the gravel was 1.0 kg. second part of the deposit, and a majority of particles travelled a long distance. Gravel Coarse sand Fine sand On the 15° slope Composite Fine sand 60 Coarse sand Gravel 20 20 0 5 10 15 Angle of the lower slope [˚] Figure 10 Run-out of the main part of the deposit for the 0 102030405060 polydisperse material (M =M =M = 1.0 kg) on different slopes, g c f Run-out [cm] comparing with the run-outs for the three monodisperse Figure 8 Deposit morphologies of the main part of the deposit materials. The error bars show standard error of the average run-out for the three monodisperse materials on the 15° slope. for each test. Deposition height [mm] Deposition height [mm] Mass of the second part of the Run-out [cm] deposit [g] Yang et al. Geoenvironmental Disasters (2015) 2:12 Page 6 of 9 was involved. These rollers threw into disarray so that the particles might be either blocked or forced into sliding. 0° Furthermore, from the point of view of energy, the energy 5° was consumed significantly due to interegranular friction 10° when excessive amount of fine sand was involved that the 15° gravel was embedded in a matrix of fine sand. When F was small (0 < F ≤0.2), the flows with 1.8 kg f f gravel (blue line, Figure 13) exhibited the highest mobil- ity. This implies that the polydisperse material contain- ing more coarse particles might travel farther than that with less coarse particles at small F . The main cause may be that the gravel typically had a high porosity, and the interactions between particles would be reduced by 020 40 60 80 100 120 substituting a coarse particle for the same mass of fine Run-out [cm] particles. Frictional loss was proportional to the surface area of particles available for the interactions, and thus Figure 11 Deposit morphology of the main part of the deposit for the polydisperse material (M =M =M = 1.0 kg) on the less energy was consumed by intergranular friction when g c f different slopes. the mass of the gravel increased. The flow with 1.8 kg gravel at F = 0.13 (1.8 kg gravel, Figure 13 shows the run-outs of flows on the 15° slope, 0.8 kg coarse sand, and 0.4 kg fine sand) travelled the which were consisting of coarse and fine particles: gravel longest run-out of 109 cm; the maximum run-out of as coarse particle, and coarse and fine sand as fine 102 cm was observed for the flow with 1.4 kg gravel at particle. The mobility was enhanced due to the interac- F = 0.27 (1.4 kg gravel, 0.8 kg coarse sand, and 0.8 kg tions between particles on the 15° slope, except in the fine sand), and the peak in run-out was 98.3 cm for the case with 1.0 kg gravel and 2.0 kg fine sand where the flow with 1.0 kg grave at F = 0.27 (1.0 kg gravel, 1.2 kg run-out of this polydisperse material was significantly coarse sand, and 0.8 kg fine sand). For the polydisperse smaller than that of the three monodisperse materials. materials with different mass of gravel, the flows exhib- The trend of run-outs for the polydisperse materials in ited the highest mobility at different F . The interaction the three series was similar. The run-outs increased with of particles with different sizes and shapes became more F until reaching a peak, and then decreased with further complicated when internal structure of granular flows increasing F . This suggests that a certain amount of fine was varied. The precise details of interactions among sand advanced the mobility of granular flows, and exces- constituent particles are still poorly understood. sive amount of fine sand obstructed their propagation. The flows containing 1.8 kg gravel show a peak in The reason might be that a thin layer of fine sand acted run-out over a range of F between 0.1 and 0.2. The peak as rollers for the rolling of the gravel, leading to the re- in run-out extended over a greater range of F between duction of effective friction resistance during the move- 0.1 and 0.3 for the flows containing 1.4 kg gravel, and of ment; the interactions between particles became more F between 0.1 and 0.4 for the flows containing 1.0 kg complicated than they just acted as a single-row roller to gravel. The peak was sharper in the experiments with lubricate the gravel when excessive amount of fine sand 1.8 kg gravel. This suggests that the mobility was more 3.0% 2.6%2.6% first time second time third time 2.5% 1.9% 2.0% 1.8% 1.6% 1.5% 1.5% 1.5% 1.5% 1.2% 1.1% 1.0% 1.0% 0.8% 0.5% 0.0% 0 5 10 15 Angle of the lower slope [˚] Figure 12 Mass of the second part of the deposit for the polydisperse material (M =M =M = 1.0 kg) over three runs on g c f different slopes. Deposition height [mm] Mass percentage of the second part of the deposit [g] Yang et al. Geoenvironmental Disasters (2015) 2:12 Page 7 of 9 120 120 Mg=1.0 kg Mg=1.0 kg 100 Mg=1.4 kg 100 Mg=1.4 kg Mg=1.8 kg Mg=1.8 kg On the 5° slope On the 15° slope 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Fine sand mass fraction Fine sand mass fraction Figure 15 Run-outs of the main part of the deposit for the Figure 13 Run-outs of the main part of the deposit for the polydisperse materials with various fractions of fine sand on polydisperse materials with various fractions of fine sand on the 5° slope. The error bars show standard error of the average the 15° slope. The error bars show standard error of the average run-out for each test. run-out for each test. sensitive to the proportion of fine sand when more coarse and fine particles on enhancing the mobility of gravel was involved. polydisperse materials was not fully developed on the The run-outs of flows on the slope of 10°, 5°, and 0° gentle slopes, i.e. the rolling motion did not readily are shown in Figures 14, 15, and 16, respectively. The occur on the gentle slopes. On the 5° and 0° slope, the polydisperse materials also travelled farther than the run-outs were almost identical at large F (0.3 ~ 0.67) three monodisperse materials on these slopes. The regardless of the mass of gravel. This was because the trends of run-outs were similar to that on the 15° slope. gravel embedded in a matrix of fine sand and was diffi- However, the run-outs on the gentle slopes were shorter cult to move on these gentle slopes. than that on the 15° slope. This indicates that the in- Figure 17 shows the deposit morphology of the main clination of the lower slope significantly influenced the part of the deposit accumulated on the lower slope with mobility of polydisperse materials. The difference in different inclinations. The three flows, consisted of vari- run-out was not significant for a range of F on these ous constitute particles, were selected for comparison. gentle slopes, comparing with that on the 15° slope. Each of the three flows (M = 1.0 kg, M = 1.2 kg, M = g c f This implies that the effect of the interactions between 0.8 kg; M = 1.4 kg, M = 0.8 kg, M = 0.8 kg; M = 1.8 kg, g c f g 120 120 Mg=1.0 kg Mg=1.0 kg 100 100 Mg=1.4 kg Mg=1.4 kg Mg=1.8 kg Mg=1.8 kg 80 80 60 60 40 40 On the 0° slope On the 10° slope 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 Fine sand mass fraction Fine sand mass fraction Figure 14 Run-outs of the main part of the deposit for the Figure 16 Run-outs of the main part of the deposit for the polydisperse materials with various fractions of fine sand on polydisperse materials with various fractions of fine sand on the 10° slope. The error bars show standard error of the average the 0° slope. The error bars show standard error of the average run-out for each test. run-out for each test. Run-out [cm] Run-out [cm] Run-out [cm] Run-out [cm] Yang et al. Geoenvironmental Disasters (2015) 2:12 Page 8 of 9 morphology of granular flows was also influenced strongly by the inclination of the lower slope. The deposit profile a) Mg=1.8 kg; Mc=0.8 kg; Mf=0.4 kg was much flatter and longer on the steep slopes (15° and 10°) than that on the gentle slopes (5° and 0°). This 15˚ phenomenon implies that there was a critical inclination 25 10˚ of the lower slope between 5° and 10° at which particle 5˚ motion in flows changed in this work. When the slope was steeper than the critical inclination, the particles 0˚ were prone to rolling. Otherwise, the particles exhibited sliding motion. For all polydisperse materials used in the experiments, the deposits exhibited some common features as follows. First, coarse particles segregated to the surface of fine 0 20406080 100 120 particles. This phenomenon is also observed frequently Run-out [cm] in field investigations. Second, the region of maximum concentration of particles was farther from the flow origin on the steeper slope, that is, more materials were b) Mg=1.4 kg; Mc=0.8 kg; Mf=0.8 kg transported a long distance. A broad range of granular materials accumulated from the position 20 cm to 15˚ 90 cm on the 15° and 10° slopes. On the gentle slopes, 10˚ however, the deposits concentrated a narrow range from the position 0 cm to the position 40 cm. The materials 20 5˚ were prone to contribute to add the deposition height 0˚ rather than the run-out on the gentle slope. Finally, the deposit morphologies were almost similar on the same slope for the three flows with different polydisperse components. This implies that the mobility of granular flows was more sensitive to the inclination of the lower 0 20 40 60 80 100 120 slope than granular component. Run-out [cm] Method The flows described in this study varied the proportion c) Mg=1.0 kg; Mc=1.2 kg; Mf=0.8 kg 35 of constitute particles but maintained the same total mass to examine the effect of interactions between parti- 15˚ cles on the mobility of granular flows. 10˚ Results 5˚ Test results indicate that the run-outs of the flows with 0˚ a wide range of grain sizes were larger than the flows only containing mono-sized particles. The proportion of fine sand strongly influenced the run-out of the polydis- perse materials. The fine sand was transported with the gravel, and 0 20406080 100 120 naturally segregated to the base of the flow under grav- ity. The rolling of fine sand acted as a lubricant for the Run-out [cm] gravel by the interactions with each other, and thus the Figure 17 Deposit morphology of the main part of the deposit friction resistance reduced during the movement. With accumulated on the lower slope with different inclinations: a) M = 1.8 kg; M = 0.8 kg; M = 0.4 kg; b) M = 1.4 kg; M = g c f g c increasing F , a greater proportion of gravel was com- 0.8 kg; M = 0.8 kg; c) M = 1.0 kg; M = 1.2 kg; M = 0.8 kg. f g c f pletely supported by the fine sand, and the run-out reached its peak. This indicates that rolling motion was M = 0.8 kg, M = 0.4 kg) typically exhibited the longest very important in flow propagation, and increasing c f run-out in the series on the 15° slope. The deposit proportion of rolling to sliding in particle motion re- morphologies on the steep and gentle slopes significantly duced energy consumption. However, the run-out de- departed from each other. This indicates that the deposit creased with further increasing F . This was because Deposition height [mm] Deposition height [mm] Deposition height [mm] Yang et al. Geoenvironmental Disasters (2015) 2:12 Page 9 of 9 intergranular friction dominated which was the primary of Mountain Hazards and Environment, Chengdu 610041, China. Department of Environmental Engineering Science, Gunma University, Kiryu source of energy loss, and thus limited the propagation 376-8515, Japan. of granular flows. The deposit characteristics on the steep and gentle Received: 11 October 2014 Accepted: 25 February 2015 slopes significantly departed from each other. The deposit profile was much flatter and longer on the steep slopes References (15° and 10°) than that on the gentle slopes (5° and 0°). Balmforth NJ, Kerswell RR (2005) Granular collapse in two dimensions. J Fluid Mech 538:399–428 The region of maximum concentration of particles was Blasio FVD, Crosta G (2014). Simple physical model for the fragmentation of rock farther from the flow origin on the steeper slope, i.e., avalanches. 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Phillips JC, Hogg AJ, Kerswell RR, Thomas NH (2006) Enhanced mobility of granular mixtures of fine and coarse particles. Earth Planet Sci Lett 246:466–480 Competing interests Pouliquen O (1999) Scaling laws in granular flows down rough inclined planes. The authors declare that they have no competing interests. Phys Fluids 11(3):542 Pudasaini SP, Hutter K (2003) Rapid shear flows of dry granular masses down Authors’ contributions curved and twisted channels. J Fluid Mech 495:193–208 FC and KU laid out the experiment scheme and provided discussions about Pudasaini SP, Wang YQ, Sheng LT, Hsiau SS, Hutter K, Katzenbach R (2008) the test results; QY and ZS conducted the small flume tests; QY and ZS Avalanching granular flows down curved and twisted channels: Theoretical drafted the manuscript; all authors read and approved the final manuscript. and experimental results. Phys Fluids 20:073302 Roche O, Gilbertson MA, Phillips JC, Sparks RSJ (2006) The influence of particle Acknowledgement size on the flow of initially fluidized powders. Power Technology 166:167–174 This work is supported by National Natural Science Foundation of China Scheidegger AE (1973) On the prediction of the reach and velocity of (project No. 41402244), the Fundamental Research Funds for the Central catastrophic landslides. Rock Mech 5:231–236 Universities (project No. A0920502051413-13), and Scientific Research Yang QQ, Cai F, Ugai K, Yamada M, Su ZM, Ahmed A, Huang RQ, Xu Q (2011) Foundation for Returned Scholars, Ministry of Education of China. This Some factors affecting mass-front velocity of rapid dry granular flows in a research is also partly supported by the Chinese State Key Basic Research large flume. Eng Geol 122:249–260 Program (project 2013CB733201). Much gratefulness is extended to the two Yang QQ, Cai F, Su ZM, Ugai K, Xu LY, Huang RQ, Xu Q (2014) Numerical anonymous reviewers and the editors, and their comments strongly contributed Simulation of Granular Flows in a Large Flume Using Discontinuous in improving the quality of this manuscript. Deformation Analysis. Rock Mech Rock Engng 47(6):2299–2306 Author details Faculty of Geosciences and Environmental Engineering, Southwest Jiaotong University, Chengdu 610031, China. Chinese Academy of Sciences, Institute

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Geoenvironmental Disasters – Springer Journals

Published: Apr 25, 2015

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