人工降雨条件下冲沟型泥石流起动试验研究

下垫面以位于贡嘎山东坡的熊家沟为模型,开展了不同降雨强度条件下冲沟型泥石流起动的模拟试验,初步研究了冲沟型泥石流的形成机理和演化特征.试验研究表明:(1)在强降雨条件下,水体入渗速度、不同深度土体含水量变化与降雨强度呈反比例关系,降雨强度越大,越不利于水体入渗,而有利于坡面汇流、冲沟径流和下切侵蚀; (2)在强降雨和径流条件下,土体破坏方式、破坏程度以及泥石流形成机理表现出差异性.相对较小雨强降雨条件下,土体破坏方式以滑坡为主,泥石流形成模式表现为滑坡液化与转化起动,雨强较大降雨条件下,土体破坏方式以侵蚀垮塌为主,泥石流形成模式为洪流席卷垮塌体和沟床揭底; (3)起动试验中泥石流阵性特征明显.在强降雨条件下,雨强与泥石流的规模、黏度之间没有正相关性,雨强越大,泥石流黏度越小,试验中多出现的是高含砂洪流,而相对较小雨强作用下由土体液化转化形成的泥石流黏度较大.试验现象和结果与熊家沟泥石流起动、发生过程具有较高的一致性.

FIELD EXPERIMENTS FOR GROOVE-TYPE DEBRIS FLOW INITIATION WITH ARTIFICIAL RAINFALL

Debris flows can occur abruptly and rapidly in mountainous areas. It is difficult to observe their occurrence process. Therefore, field experiment becomes an important method to study debris flow initiation mechanism in recent years. This paper takes Xiongjia gully as an example and uses artificial rainfall experiment to study initiation of groove-type debris flow. Experimental results indicate some relations among rainfall intensity and gully erosion, slope stability and failure mode, debris flow initiation mechanism and characteristics. Conclusions are drawn as follows:(1)Under strong precipitation, infiltration rate and soil water content at different depths are inversely proportional with rainfall intensity. Intense rainfall favors overland flow, gully runoff and erosion, but is not conducive to water infiltration. (2)Slope failure modes and debris flow initiation mechanism are various under different rainfall and runoff conditions. Under the condition with rainfall intensity of 55mmh-1, the slope failure mode presents soil liquefaction and landslide. Accordingly, debris flow initiation mechanism belongs to landslide conversion. However, under the condition of intense rainfall and runoff, gully beds are easily to be eroded and slopes are prone to collapse. Then, debris flows occurred with initiation mechanism of entrainment. (3)In terms of debris flow characteristics, debris flow occurrence process consists of several intermittent flows. In addition, debris flow magnitude and flow viscosity are not consistent with rainfall intensity. On the contrary, under condition of intense rainfall of 65mmh-1 and 75mmh-1,debris flows tend to be watery. But with rainfall condition of 55mmh-1, the flow viscosity is higher. The experimental results are well consistent with the natural debris flow occurrence at Xioangjia gully.