考虑漂木作用的泥石流堰塞体稳定性分析实验研究

The material and structure characteristic of barrier dams is a most important key factors that affects the stability and break mechanism. Driftwood, as an organic debris in landslide dams, is much different with sand and gravel. However, there is lack of research on the influence of driftwood to the stability of barrier dams. This project mainly focuses on the dams caused by debris flow with driftwood. The following contents are included in the study: Firstly, the structure characteristic of debris flow dams with driftwood will be theoretically analyzed from the perspective of separation mechanism of soil-stone-driftwood pile in the forming of damming body. Field observation samples and formation simulating model test results will be used to verify the theoretical dam structure models. Based on the results, hydraulic model tests on the overtopping break of the debris flow dams with driftwood will be carried out. The process of overtopping and peak discharge will be measured and compared with non-driftwood debris flow dams. Thus how the influence of driftwood parameters such as the quantity and the distribution to overtopping break will be discussed. Meanwhile, the permeability of the debris flow dams with driftwood will also be studied according to flume infiltration devices. Permeability coefficients of different cases will be measured and analyzed. A discriminate formula for the seepage failure of debris flow dams with driftwood will be proposed based on the experimental data. Finally, a method of stability assessment for debris flow dams with driftwood will be provided by considering the effects of driftwood to overtopping and permeability as well as the results of stability evaluation indexes such as the blockage index Ib, impoundment index Ii and dimensionless block index DBI. With these studies, the effects of driftwood to the stability of debris flow dams will be clearer, and thus it can provide a basis whether it should consider the effects of driftwood or not when assess the stability of debris flow dams.

堰塞体物质组成与结构特征是影响堰塞体的稳定性及破坏模式的重要内在因素之一。漂木作为一种常见于堰塞体中异于土、石颗粒的碎屑物，其对堰塞体稳定性的影响还鲜有研究。本项目拟通过考虑泥石流携带漂木形成堰塞体过程中对漂木与泥沙的分选机制，分析包含漂木的泥石流堰塞体结构组成特征，并据此提出结构特征参数体系，对于理论分析结果根据野外考察样本与模拟实验样本进行验证与补充。在此基础上，开展堰塞体的漫顶溢流破坏水槽模拟实验，探讨典型堰塞体结构下漫顶溢流溃决特征，分析漂木量、漂木分布方式等因素对漫顶溢流溃决过程的影响；用特制的渗透水槽开展堰塞体渗透性实验，分析不同结构特征下的堰塞体渗透性及可能发生渗透破坏的条件。最后，以稳定性统计指标分析为基础，综合考虑漂木对漫顶溢流侵蚀破坏与渗透性的影响，提出考虑漂木作用的泥石流堰塞体稳定性评估方法。通过该项研究，为堰塞体的稳定性评估考虑漂木的影响提供理论和数据支持。

堰塞体物质组成与结构特征是影响堰塞体的稳定性及破坏模式的重要内在因素之一。漂木作为一种常见于堰塞体中异于土、石颗粒的碎屑物，其对堰塞体稳定性的影响还鲜有研究。本项目通过实地调查、试验模拟、理论分析等方法，分析了包含漂木的堰塞体结构特征，开展堰塞体的漫顶溢流溃决破坏模拟试验。研究结果表明，堰塞体中包含漂木的现象普遍存在，漂木在堰塞体中的分布可用二元结构模型来描述，主要分为上下二元结构和前后二元结构。其中，上下二元结构多发生在泥石流自然堆积过程中，漂木多停留在泥石流堆积体表面；前后二元结构多发生在沟道中有障碍物阻挡的情况下，根据漂木堵塞率和堵塞形态又可以分为关键漂木拦挡型和大量漂木咬合型堵塞体。堰塞体中的漂木会对堰塞体的稳定性起负面作用，无论漂木分布方式、分布数量和漂木长度如何。堰塞体中存在漂木，堰塞体溃决过程会缩短，溃决峰值流量显著增加，侵蚀速率显著增大。其中，溃决峰值流量系数随着漂木长度的增大和漂木量的增大呈先增大后减小的抛物线型，最大可达无漂木堰塞体的两倍。在试验条件下漂木长度与坝体长度的比值达到0.67时，漂木体积与泥沙堆积体积的比值为0.002时，溃决峰值流量系数达到最大。除了漂木组分的影响外，土石组分在堰塞体中的分布特征对堰塞体的溃决也存在影响。根据坡体特征与滑坡堰塞体物质分布特征之间的关系，得出了不同坡体特征下堰塞体的物质分布类型，主要包括均匀混合型、上粗下细型和叠瓦堆积型。构造相应特征的堰塞体，发现在坝体材料整体颗粒级配相同而坝体内部物质组成分布不同的情况下，堰塞坝的溃决过程基本相同，即均可分为渗流侵蚀阶段、溯源侵蚀阶段、溃口迅速发展阶段及粗化平衡四个阶段，但不同阶段呈现明显的差异性特征。研究结果为堰塞体的稳定性影响因素及评价方法提供了新的依据。

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