堰塞坝溃口下切过程试验研究

Experiments Investigation on Longitudinal Breaching of Natural Dam

针对堰塞坝溃口下切过程和不同因素对过程影响的问题,开展室内水槽试验。结果表明:溃口下切过程分3个阶段:Ⅰ为溃口缓慢发展阶段,即水流缓慢溢出溃口阶段,侵蚀速率较小,泥沙输移主要以悬移质运动为主,溃口下切缓慢;Ⅱ为溃口迅速发展阶段,表现为溯源侵蚀强烈,溃口底部变化迅速,推移质运动占主导地位;Ⅲ为稳定河床形成阶段,水流速度和流深减小,水流携沙力减弱,河床形成粗化层,最终达到新的水沙平衡。溃口流量与侵蚀的关系表现为:来水流量的加大增加了相应时刻的溃决流量,增大了侵蚀率,缩短了溃决时间,溃口底部趋于平滑;来水流量的加大提高侵蚀率曲线斜率,使侵蚀率曲线向瘦高型发展;随背水坡坡度的增加,溃决流量增大,侵蚀率增加,坝体残留高度降低。另外,因背水坡坡度增加导致坡面土颗粒稳定性的降低可采用水槽坡度与背水坡坡度之和正切值的3次方这一因子反映。考虑堰塞坝材料性质差异性的溃决过程是下一步研究的重点。

In order to obtain the progress of longitudinal erosion and effects of different factors,6 flume tests were conducted. The results indicated that the longitudinal erosion process included 3 stages. At stage I , the outflow was slow, and the suspended load was transports to downstream mainly during the process. At stage II , the depth of the breach changed rapidly. The bed load was transports fiercely due to backward erosion. At stage Ⅲ,the Velocity and rateof outflow decreases, armor laYer is formed which protects the sediment under the armor layer from eroding. At last, dynamic equilibrium was achieved between the water phase and sediment phase. With inflow rate in- creasing, the breach time decreases and outflow discharge increased, leading to greaterstream power and highererosion rate. And the bot- tom of the breach become smoothly due to large inflow rate. The slope of the erosive characteristics curve become larger with the outflow discharge increasing. The shape of erosive curve changed from multi-peak curve to mono-peak curve with downstream slope increasing. The steepslope of downstream also increased the outflow discharge and erosion rate, and decreased the residual height of the dam. The factor J3 which was equal to the third power of tangent values of the bed slope and downstream slope＇ s summation, could reflect the stability of soil particles in different downstream slopes.