堰塞坝背水面坡度对溃决过程影响机理大尺度试验

堰塞坝溃决物理概化试验是当前研究堰塞坝溃决机理较为可行的方法，但在现有堰塞坝溃决试验中，由于试验坝体尺寸较小、试验上游库容不足，导致试验的溃决过程与实际堰塞坝溃决存在较大差异。为尽量克服库容的不足所带来的影响，本文采用了最大库容达380m3的大尺度堰塞坝溃决试验系统。本文以无粘性、宽级配砂砾料堰塞坝为对象开展了多组室内大尺度溃决试验来揭示堰塞坝溃决机理，并通过设置不同背水面坝坡来研究其对溃决过程的影响。通过试验发现堰塞坝溃决过程可以分为沿程冲刷、溯源冲刷、快速发展和溃口稳定四个阶段。在溃决过程中发现陡坎侵蚀和溃口两侧土体失稳坍塌是溃口快速发展的主要机理。不同背水面坡度下的沿程冲刷阶段冲蚀特征基本相似，而溯源冲刷阶段及快速发展阶段溃决过程差异显著，较大的背水面坡度使溯源冲刷阶段跌坎水流更容易得到发展，进而影响溃口处的垂向冲深及侧向发展，导致快速发展阶段更易形成垂向落差较大的陡坎洪水冲蚀。从溃决历时来看，坡度的增加使溃口发展更快、峰值流量出现时间更早，进而导致溃决历时缩短。坝顶溃口宽度及峰值流量也会随着坡度的增加而增加。在本试验还较好地重现了天然堰塞坝下游河道两岸的淤积现象，并根据堰塞坝溃决过程中的水流特点、泥沙运动及溃决完成后下游河道的地貌，初步分析了淤积区的形成机理。

Large-scale Experiment on Impact of Downstream Slope on Breaching Mechanisms of Landslide Dams

Laboratory experiments are one of useful approaches for investigate landslide dam breaching. However, due to the small size of the dam and limited storage volume of the landslide lake , the dam breach process in the existing experiment differs much from that of the natural landslide dam breach. A large-scale landslide dam breaching experiment system was built with the lake volume up to 380 m3. Series of large-scale tests were conducted to investigate influence of the downstream slope of the landslide dam comprising of non-cohesive wide-graded sand-gravel material. It was found that the breaching process of landslide dam can be divided into four stages: longitudinal erosion, back-ward erosion, rapid development and stabilization stage. The characteristics of erosion in different stages were quite different.During the breach process, it is found that the erosion of steep slope and the collapse of soil on both sides of the outburst are the main mechanisms of the rapid development of the outburst. Along the erosion stage under different longitudinal erosion is similar characteristics, and the back flushing and rapid development phase flows process significant difference, the larger dorsal surface slope makes it easier for back flushing stage and water drop was developed, which affect the dyke in deep of vertical and lateral development, lead to rapid development phase are more likely to form a vertical gap bigger scarp flood erosion. The erosion process varied greatly under different downstream slope conditions: With a higher downstream slope of the landslide dam, the breach duration was shorter, head-cut erosion formed easier, the breach expanded faster and the peak of outburst flood appeared earlier and with a larger value. Moreover, the bed topography at the downstream channel after the flood and its formation mechanism of the deposition area on both sides of the downstream channel of the dam were primarily analyzed.