Experimental study on failure mechanism of debris flow dam
Authors: Ruan Hechun , Chen Huayong , Li Xiao , Yu Yunhan 
Published: March 2022

&lt;p&gt;As a common type of barrier dam, debris flow dam is widely distributed in alpine valley areas with abundant rainfall and active tectonic movement. In this paper, the failure mechanism of debris flow dam is studied based on flume tests. The results show that the failure mode of debris flow dam is basically overtopping failure ; the obvious retrogressive scarp can be formed in the process of debris flow dam failure. According to the longitudinal evolution characteristics of the debris flow dam failure, the breach process can be divided into three stages: the formation of a retrogressive scarp (stage &amp;#8544;), the erosion of the retrogressive scarp (stage &amp;#8545;), and its decline stage (stage &amp;#8546;). The peak discharge appears in stage II. Furthermore, a model that can describe the longitudinal evolution process of debris flow dam breach is proposed : &lt;em&gt;E=k v &lt;/em&gt;sin(0.85&lt;em&gt;+&amp;#952;&lt;/em&gt;)&lt;sup&gt;3&lt;/sup&gt;, where &lt;em&gt;E&lt;/em&gt; is the erosion rate, &lt;em&gt;v&lt;/em&gt; and &lt;em&gt;&amp;#952;&lt;/em&gt; are the flow velocity and the longitudinal slope of the breach respectively, and &lt;em&gt;k&lt;/em&gt; is the erosion rate coefficient. The larger the value of the erosion rate coefficient&lt;em&gt; k&lt;/em&gt; is, the faster the erosion rate &lt;em&gt;E&lt;/em&gt; is. The minimum correlation coefficient &lt;em&gt;R&lt;/em&gt;&lt;sup&gt;2&lt;/sup&gt; between the calculated and the measured erosion rates is 0.73. The relationship among erosion rate coefficient &lt;em&gt;k&lt;/em&gt;, grain-size distribution parameters &lt;em&gt;&amp;#956;&lt;/em&gt;, and &lt;em&gt;D&lt;/em&gt;&lt;sub&gt;c&lt;/sub&gt; is also proposed, and the correlation coefficient &lt;em&gt;R&lt;/em&gt;&lt;sup&gt;2&lt;/sup&gt; reaches 0.965. In addition, the lateral expansion process of the breach is accompanied by intermittent collapse process. The most intense collapse process occurrs in stage II, and the collapse scale and intermittent time can be described by Poisson distribution. Finally, the key influencing factors are selected for dimensionless analysis, and the empirical formula for peak dischage of debris flow dam failure is obtained: &lt;em&gt;Q&lt;/em&gt;=0.0038(&lt;em&gt;gH&lt;/em&gt;&lt;sup&gt;5&lt;/sup&gt;)&lt;sup&gt;0.5&lt;/sup&gt;(&lt;em&gt;V&lt;/em&gt;/&lt;em&gt;H&lt;/em&gt;&lt;sup&gt;3&lt;/sup&gt;)&lt;sup&gt;0.914&lt;/sup&gt;(&lt;em&gt;H&lt;/em&gt;/&lt;em&gt;D&lt;/em&gt;&lt;sub&gt;90&lt;/sub&gt;)&lt;sup&gt;0.199&lt;/sup&gt;(&lt;em&gt;P&lt;/em&gt;&lt;sub&gt;0.075&lt;/sub&gt;)&lt;sup&gt;-0.176&lt;/sup&gt;(&lt;em&gt;C&lt;sub&gt;u&lt;/sub&gt;&lt;/em&gt;)&lt;sup&gt;-0.117&lt;/sup&gt;, where &lt;em&gt;Q&lt;/em&gt; is the peak discharge ; &lt;em&gt;g&lt;/em&gt; is gravity acceleration ; &lt;em&gt;H&lt;/em&gt; is the dam height ; &lt;em&gt;V&lt;/em&gt; is the lake volume ; &lt;em&gt;d&lt;/em&gt;&lt;sub&gt;90&lt;/sub&gt; is the upper limit particle size ; &lt;em&gt;P&lt;/em&gt;&lt;sub&gt;0.075&lt;/sub&gt; is fine particle content ; &lt;em&gt;C&lt;sub&gt;u&lt;/sub&gt;&lt;/em&gt; is inhomogeneous coefficient. However, the formula needs to be further verified by practical cases. The results provide an important theoretical basis for the prediction of debris flow dam-break floods, which can facilitate evidence-based decision-making in disaster prevention and mitigation.&lt;/p&gt;