木石堰塞坝的溃决特征和机理试验研究

EXPERIMENTAL STUDY ON BREACHING CHARACTERISTICS AND MECHANISM OF LANDSLIDE DAMS WITH WOOD

堰塞坝是由滑坡、崩塌等动力过程形成的堵塞沟道的天然坝体,其结构松散、材料分布不均,极易发生溃决,给下游群众的生命财产安全带来极大危险。在植被良好地区发生的滑坡往往携带大量的漂木,含有漂木的堰塞坝溃决特征研究还很匮乏。通过模型试验,探讨了3种含有漂木的堰塞坝(木石堰塞坝)溃决特征,即漂木横向分布的堰塞坝(DWC)、漂木纵向分布的堰塞坝(DWL)和漂木随机分布的堰塞坝(DWR)分析了漂木不同分布方式、不同长度、不同规模等因素对堰塞坝溃决参数的影响。结果如下:(1)相较砂石坝而言,木石坝溃口形成阶段历时更长而溃口发展阶段历时更短,木石坝的溃决峰值流量是砂石坝的1.5~1.7倍,峰值流量放大系数达6.7~8.2。(2)木石坝溃决过程中产生显著的深潭侵蚀现象,溃口纵剖面线呈现明显的陡坎,深潭侵蚀程度与漂木的分布方式、漂木量、漂木长度有关。漂木横向分布条件下深潭侵蚀时间最长、侵蚀坑最大;且漂木越长、漂木量越大,深潭侵蚀持续时间越长,溃口下切速率越大。(3)漂木对堰塞坝溃决产生作用的机理主要表现为溃口下切时的深潭侵蚀作用、对溃口侧面的支撑作用(漂木纵向分布时)和对坝体的锚固作用(漂木横向分布时)。研究成果表明,漂木对堰塞坝溃决特征影响显著,在堰塞坝稳定性分析及风险评估中不可忽视。

Landslide dams are natural dams blocking river channels formed by landslides,collapses,and so on.Landslide dams are prone to breaking due to their loose structure and heterogeneous material distribution,which poses a great danger to the lives and property of downstream populations.Landslides that occur in well-vegetated areas often carry huge amounts of wood.Studies on the stability and breach characteristics of landslide dams with wood(DW)are relatively few.According to model tests,we discussed the breaching characteristics of three types of DW dams:landslide dams with wood transversely distributed(DWC),longitudinally distributed(DWL),and randomly distributed(DWR).The influences of the distribution style,length,and volume of wood on the failure of landslide dams were analyzed.The results are as follows:(1)The duration of the breach formation stage of the DW dams is generally longer than that of landslide dams without wood,while the duration of the breach development stage is shorter.The outflow peak discharges of the DW dams are 1.5-1.7 times larger than those of landslide dams without wood.The amplification coefficients of the outflow peak discharge of DW dams range from 6.7 to 8.2.(2)There is significant deep-pool erosion phenomenon in the breaching process of DW dams,and obvious erosion pits occur in the longitudinal profile of the breach.The degree of deep-pool erosion is related to the distribution,length,and volume of wood,among which the wood distribution exerts the most significant influence on the breach characteristics.The deep-pool erosion lasts the longest and the erosion pit is the largest under DWC conditions.The erosion pit moves vertically downward for DWL,while it moves both vertically downward and headward for DWC.The larger the volume and the longer the wood log,the longer the deep-pool erosion lasts and the greater the undercutting rate.(3)The mechanisms by which wood affects dam break lie in the deep-pool erosion in the breach undercutting process,the supporting effect on the bank side(when wood is longitudinally distributed),and the anchoring effect on the dam body(when wood is transversely distributed).The research results demonstrate that wood in landslide dams has an obvious influence on breach characteristics,which cannot be ignored in the stability analysis and risk assessment of landslide dams.