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.