Model Testing and Rheology of a Fine Grain Rich Debris Flow
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Debris flows are a hazardous type of landslide, primarily caused by intense precipitation in steep mountainous terrain. Water, soil and debris mix to form a slurry that advances rapidly downslope, growing in size as it entrains more and more mass. They occur all over the world and are prevalent in canyons and steep gullies. They are considered to be one of the most dangerous landslide types, due poor predictability, a rapid onset, high mobility and high destructive powers. To investigate the flow behaviour of fine grain rich debris flow, rheological experiments and physical modeling has been conducted.The rheology has primarily been investigated using viscometer testing. Six viscometer tests were conducted. It was shown that fine grain rich soil material behaved as a shear thinning material exhibiting a yield strength and could be modeled using Herschel-Bulkley rheology. 22 flume model tests were conducted using the same, fine grain rich material as for the viscometer tests. Velocities, flow heights and impact forces were measured and analysed. Two different soils were used, where the primary difference was the size of the clay fraction. Tests were conducted using different solid concentrations and quickness values. Coefficients for two simple hydraulic models (static and dynamic) were calculated from the results. The results indicate that the effect of variations in quickness value or solid concentration decreases as the flow volume is increased.The effect variations in quickness value appears to be complex. An extremum for the middle quickness value was observed in the velocity, flow height and impact force results. This implies that at least two effects are acting against each other when the quickness value is increased.