山洪中漂木在拦砂坝前堵塞堆积实验

Experiment on the Clogging and Deposition of Woody Debris Flowing with Torrents in Front of Debris Dams

山洪和泥石流中夹带的漂木在拦砂坝开口处易造成严重堵塞,使坝体对后续流体的分选效果减弱或失效,甚至进一步威胁坝体安全,因此探讨漂木在拦砂坝前的堵塞堆积规律和影响因素对于工程结构设计具有重要意义。考虑漂木长度L、溢流口开口宽度b、漂木量Vw及流体流量V等因素对漂木形成堵塞的影响,通过实验研究了山洪中漂木在拦砂坝前堵塞堆积规律。实验发现漂木在拦砂坝溢流口的堵塞堆积形态主要有三种:溢流口搭桥型,交错咬合型,坝前停积型。漂木堵塞率在L/b<1时基本保持不变,在1<L/b<3时,随着L/b增大先增大后减小,在L/b=2左右达到最大;漂木拦截率在L/b<2呈线性增大,在2<L/b<3保持基本稳定。漂木大量堵塞在溢流口或滞留在库容区中后部都能形成较高的漂木拦截率。漂木体积含量Vw/V在L/b<1时对漂木堵塞率和拦截率基本无影响,在1<L/b<3时,对漂木堵塞率和拦截率的影响呈增大趋势,随着L/b的增大,增大趋势越明显,在L/b=2时基本呈线性增长。

Debris flow or torrents with woody debris could weaken the disaster mitigation function or threaten the safety of debris dams for woody debris may clog densely in the spillway. Hence, it is important to study the clogging and deposition regularity of woody debris in front of debris dams for mitigation structure design. According to hy- draulic experiments, we considered the impact of woody debris length （L）, spillway width （b） , woody debris volume （ Vw ） and fluid volume（V） to the woody debris clogging and deposition. The experiment results show that there are three main types of clogging pattern in the spillway. The first one is several logs trapped transversely by the spillway and then trapping following woody debris. The second one is numerous woody debris arrive simultaneously at the spillway interlocked with each other. The third one is short woody debris deposit in Front of the dam adjacent to the spillway. The woody debris clogging rate is lower than 10% and has little change with L/b when L,（b 〈 1 ,while in- crease firstly and decrease with L/b when 1 〈 L/b 〈 3, reaching the peak at L/b = 2. The woody debris trapping rate presents a linear increase with L/b when L/b ≤ 2, and keeps steady when 2 〈 L/b 〈 3. Either debris clog in the spillway or deposit in front of dam can cause high trapping rate. The relative volume of woody debris（VJV） has little impact on the clogging rate and trapping rate when L/b〈 1, while contributes to the increase of trapping rate and trapping rate when 1 〈 Lib 〈 3 in general. The bigger L/b,the higher increase presents,with a linear increase at L/b = 2.