依据物质组成分布特征的堰塞坝溃决特征

Breach characteristics of barrier dams according to the distribution characteristics of material composition

通过模型试验,考虑堰塞坝内部物质分布特征的不同,探讨均匀混合型堰塞坝(UM)、上粗下细型堰塞坝(TCBF)、叠瓦堆积粗叠细型(PCPF)堰塞坝和叠瓦堆积细叠粗型(PFPC)堰塞坝的溃决特征。结果表明:在坝体材料整体颗粒级配相同的情况下,具有不同内部物质分布特征的堰塞坝溃决过程基本可分为渗流侵蚀阶段、溯源侵蚀阶段、溃口发展阶段及粗化平衡4个阶段,但不同坝体在不同阶段呈现明显的差异性。PCPF型堰塞坝渗流侵蚀历时最短,TCBF型堰塞坝渗流侵蚀阶段最长,后者是前者的2.5倍。UM型和TCBF型堰塞坝的溃决过程早于PFPC和PCPF型堰塞坝,UM型堰塞坝溃口下切速率最小,下切过程较匀速;PFPC型堰塞坝在溯源侵蚀阶段形成的侵蚀槽窄而深,在溃口发展初期下切速率最大,可观察到频繁的岸壁崩塌-堵塞溃口-溃决现象;PCPF型堰塞坝在溯源侵蚀阶段形成的侵蚀槽宽而浅,溃口发展阶段后期下切速率最大,下游坡面局部区域易产生滑移。不同堰塞坝条件下溃决洪峰流量放大系数也不同,大小顺序为PCPF<TCBF<UM<PFPC。研究成果表明堰塞坝内部物质组成分布特征对堰塞坝的溃决时间、溃决过程、溃决流量等都有不同程度的影响,在稳定性分析时需要考虑。

[Background]Barrier dams,formed by natural forces and accumulated loosely,are highly susceptible to breaching,posing a serious threat to life and property safety.At present,researchers pay more attention to the impact of the overall material composition of landslide barrier dam on the dam breaching and stability,and do not consider the internal distribution characteristics of the materials.Is there any influence of the distribution of material composition on the breaching and stability of landslide barrier dams?[Methods]According to previous studies,four types of landslide barrier dams were established considering the different distribution characteristics of the material,which are uniformly mixed type(UM),top-coarse and bottom-fine type(TCBF),pre-coarse and post-fine dam(PCPF)as well as pre-fine and post-coarse type(PFPC).Through model tests,the whole breaching process was recorded,and the characteristics of the breaching development and the outflow discharge were analyzed.[Results]1)Different barrier dams shared similar four breaking process,that is,seepage erosion stage,retrograde erosion stage,breach development stage and coarsening equilibrium stage,but obvious characteristics in different stages have been observed for different barrier dams.2)The duration of the seepage erosion stage of the PCPF-type dam is the shortest while the UCBF-type dam is the longest,and the latter is 2.5 times of the former.3)The overtopping failure process of UM-type dam and TCBF-type dam are earlier than that of PCPF-type dam and PFPC-type dam.The erosion rate of the UM-type dam is the smallest,and the breach development process is relatively uniform.The erosion groove of the PFPC-type dam was narrow and deep developed in the retrograde erosionstage,and local collapses of the slope bank occurred most frequently during the breach development stage,causing the highest erosion rate during the first 10 s of the breach development stage and leading to frequent collapse-clogging-breaking phenomenon.A wide and shallow erosion groove developed during the retrograde erosion stage in the PCPF-type dam.The erosion rate is the largest during the later breach development stage,and the local area of the downstream slope is prone to sliding.4)The amplification coefficients of the outburst-flow peak discharge also vary among different landslide barrier dams,sharing an order of PCPF<TCBF<UM<PFPC,reaching a value of 4.24,4.83,5.03 and 5.38 respectively.[Conclusions]The results demonstrate that the distribution characteristics of the material composition inside a landslide barrier dam have different effects on the breach time,breach process and breach flow discharge of the dam,which should be considered in the stability analysis of landslide barrier dam.