Experimental study on breach broadening process of landslide dam
LIU Dingzhu, CUI Peng, JIANG Dewang
1. Key Laboratory of Mountain Hazards and Earth Surface Processes, Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, 610041, Chengdu, China;
2. University of Chinese Academy of Sciences, 100049, Beijing, China
Abstract：[Background] Dynamic process of water and breach determines breach's profile during dam overtopping process. Dynamic processes in different sections along a breach are influenced by different flow regime. At present, research on breach broadening process is mainly focusing on a certain section and assumed this section could represent the broadening process of a dam. Knowledge of breach broadening in every section is short and the whole broadening process of a breach is a scientific question.[Methods] In order to study the whole breach broadening process in different initial conditions (height and slope), six flume experiments were designed to research. The observed data of 45 sections aimed at understanding erosion process in different sections and the influences of these initial conditions. We measured this process by using measure tools in mm accuracy and it was recorded by setting HD camera upon breach initially. Apart from this, the mechanical parameters such as the rate of water content and the density of dam were rigorously controlled for guaranteeing the same mechanical set.[Results] 1) With the development of overflow, this process could be classified into two stages according to breach's profile. The process before the end of retrogressive erosion stage was named as the Aequilate Stage, and the process after retrogressive stage was named as the Bending Stage. In the first stage, the mechanism of water and sediment is simple but in the second stage the mechanism of water and sediment is complicated. 2) Broadening process could be divided into two modes, one is Linear Mode and another is Mutation Mode, accounting for 13.3% and 86.7% of 45 sections respectively. The Mutation Mode can be further divided into Weak Erosion ProcessⅠand Strong Erosion Process Ⅱ, in which the processⅡoccurs only in the Bending Stage. 3) The scour rate in the upstream and downstream is larger than that in the middle. The distribution of scour rate is like "U". In the first process, dam in larger initial slope causes larger scour rate in the same section. With the development of overflow, the complex flow regime has obvious secondary flow characters leading to the scour rate along the breach like "S" during processⅡ. For both processes, higher dam height leads to greater erosion rate.[Conclusions] Broadening ratio is different in different section and initial conditions influence the broadening ratio along the breach, which is a complicated process. This study didn't propose formulas to calculate erosion ratio along the breach, because 6 experiments couldn't reflect the physic of broadening process. Apart from this, the new understanding of broadening process of landslide dam is beneficial to the further study of mechanism of this process.
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2017, Vol. 15 
