急陡沟道泥石流起动特征模型试验研究——以汶川县福堂沟为例

An experimental study of starting characteristics of steep-channel debris flow:a case study of the Futang gully in the Wenchuan County

急陡沟道泥石流是汶川震区发现的一类特殊泥石流,调查发现其具有物源量大、侵蚀强烈,冲出规模大等特点,是震区地质灾害治理的难点。本文以汶川县典型急陡沟道泥石流福堂沟为原型,分析了其发育条件和特征,并通过模型试验等手段,还原并分析了急陡沟道泥石流起动及形成的过程,以及相应的土体内部参数变化特征。试验显示在20°、25°、30°的坡度和480mL/s、410mL/s、360mL/s的径流量的试验条件下,泥石流分别以不同的方式起动(沟床侵蚀型、滑坡流态化起动型、消防管起动型),同时结合实验过程中土体内部孔隙水压力及体积含水率变化特征的研究,详细还原了相应的泥石流起动全过程。试验数据的分析结果显示,在不同的起动方式下,土体内部的数据变化表现出不同的特征:其中,不同试验条件下的泥石流起动孔隙水压力呈现出规律性差异,即水槽坡度、径流量越大,泥石流所需的起动力越小;此外,坡度越大,土体所需的饱水时间越长,而在相同坡度下,流速越大,预饱水时间越短;研究还发现,泥石流的爆发时间与沟床坡度呈反比,并且径流量越大,泥石流持续时间也越长。基于实验结果,通过相似理论计算得到的泥石流起动流速,与实际情况一致,表明本的研究结论可为汶川震区急陡沟道泥石流的研究提供参考。

The steep-channel debris flow is special type of debris flow in the Wenchuan earthquake zone characterized by a large quantity of source material,intense and large scale erosion thereby increasing the difficulty of geological disaster management in the earthquake area.This study analyzes the development conditions and characteristics of the steep-channel debris flow in the Futang gully and experimentally reproduces them to analyze the starting characteristics of steep-channel debris flow.The results show that under the test conditions of the slope of 20°,25°,30°and the runoff of 480 mL/s,410 mL/s and 360 mL/s,the debris flow begins in different ways(trench bed erosion type,landslide fluidization starting type,fire pipe starting type).Simultaneously,by combining the study of the variation characteristics of pore water pressure and volume moisture content in the soil during the experiment,the whole process of debris flow onset was reviewed in detail.The analysis of the test data show that the soil properties vary under different starting modes:①the starting pore water pressure of debris flow under different test conditions shows a systematic difference,i.e.the larger the slope and runoff from the source,smaller the driving force required by the debris flow;②larger the slope,longer the water saturation time required by the soil.At the same slope,greater the flow rate,shorter is the pre-water saturation time;③the outbreak time of debris flow is inversely proportional to the slope of gully bed,and larger the runoff,longer the duration of debris flow.Based on the experimental results,the starting velocity of debris flow calculated by the similarity theory is consistent with the field situation demonstrating that the conclusions of this study can provide a framework for the study of the rapid and steep channel debris flow in the Wenchuan earthquake area.