Experiments on Debris Flow Migration in the Process of Overlapping Deposition
A debris flow fan is a typical debris flow sedimentary facies,which generally suffered from overlapping and accumulating by multiple debris flow torrents,and has randomness in spatial and temporal distribution,with anisotropic features such as mainstream migration and oscillating sedimentation,all of which brings difficulties in rational planning and utilization of piedmont beach-land created by debris flow sedimentation.In this paper,a debris flow fan located at the Duiwoliangzi gully,Lianghebao village,Pingwu county,Sichuan province,China was surveyed and exemplified to reveal the formation of debris flow fan created by overlapping and accumulating of multiple debris flow torrents;a series of flume experiments equipped with 3D scanning devices and a set of pressure sensors was conducted to measure the phrasal changes of fluid regime in the process of creating a debris flow fan by artificial multiple debris flow release.The genesis of mainstream migration in the fan and resulting debris accumulation shift was examined.(1)Mainstream migration in debris flow fan was controlled mainly by the density of debris flow fluid.The higher density of the fluid,the more possible it was to an overall mainstream deviation;the lower the density,the easier it to form debris body wedging into old underlying fan.(2)The migration occured not quite along lower relief of the fan,but depended mainly on the properties of a following wave of flows.(3)An empirical formula for estimating of deviation angle and distance was proposed in terms of flow density,velocity and fan morphology.The research provides a theoretical basis for understanding the formation,disaster range and evolutionary trend of debris flow fans.
debris flow fanmulti-phase depositionflow transitiondeviation from mainstream
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