Experimental Study On The Clastic Deposition Forming Debris Flow

Debris flow is one of the typical geological disaster in the mountainous areas, it is very harmful. Debris flow is controlled by three main factors, loose materials, water source and topographic conditions, its starting mechanism which can be divided into bed starting type, dam-break type and other types, one type is due to earthquake or strong rainfall causes the channel produced landslide and collapse to form clastic flow. The clastic produced in the channel and make up of accumulation of loose solid materials, it provides more material source of debris flow, changing the material sources of forming debris flow.Through field investigation found that this kind of debris flow are forming by landslide that happened in gully and collided into clastic, then forming debris flow under rainfall, such as the Niujuan gully, Wenjia gully, Guanling Dazhai gully. These gullies which forming debris flow are due to the large number of sources come from landslide happened in gully. The source conditions has fundamental change by that and make the gully turn into typical debris flow. The characteristics of clastic accumulation which forming debris flow under water resources condition has a significant effect.In this paper, according to analyze the characteristic of landslide-clastic flows, using experimental study to analyze the impact of4basic parameters which clastic flows forming debris flow:clastic surface slope, soil clay content, median grain size and non-uniformity coefficient. Through the simulation experiment of debris flow formation procession, analyzed the relationship of each factor in forming debris flow and discharge per unit width, according to relationship of various factors and discharge per unit width, fitting out a comprehensive formula of forming debris flow and gully digging up flow. Study relationships of the clastic flow characteristics and its formation of debris flow, draws the following conclusions:(1) Landslide clastic flows happened in the basin which occurred landslide and slide into the gully and disintegrate in loose materials where deposits in the gully, the formation of a large number of loose materials becoming debris flow source in the gully, it has fundamental changed the source conditions of debris flow, The huge amounts of clastic flows change the non-debris flow gully into active type of debris flow directly. The characteristics of main influence factors of forming debris flow are the characteristics of clastic flows.(2) Through the analysis of the landslide clastic deposition of, identified four main factors that may affect the formation of debris flow:surface slope of clastic deposition(°), clay content in clastic deposition(%), the median diameter of d50(mm), non-uniform coefficient Cu. Through24effective experiment, analyzes the required unit width discharge of clastic deposition forming debris flow in each single variable factors. Analysis results indicate:The surface slope of clastic deposition designed in experiments has no significant effect to forming debris flow with discharge per unit width; clay content of clastic deposition in not more than5%only affect the detritus erosion of deposition, had no significant effect to the required discharge per unit width of digging up; the impact of the required discharge per unit width in forming debris flow of clastic deposition is mainly the median diameter d50and non-uniformity coefficient Cu.(3) Through8groups of experiments obtained the required discharge per unit width with different median size of clastic deposition in forming debris flow and digging up, fitting required unit width discharge experience formula of the median particle size of d50and the formation of debris flow Q1=A1(d+1.262), the required unit width discharge experience formula of the median particle size of d50and digging up of debris flow Q2=A2(d+0.987)(Q1,Q2are unit width discharge; A1,A2are coefficient; d is relative median diameter).(4) Through8groups of experiments obtained the required discharge per unit width with different non-uniform coefficient of clastic deposition in forming debris flow and digging up, fitting required unit width discharge experience formula of the non-uniform coefficient Cu and the formation of debris flow:Q1=B1Cu0.211, the required unit width discharge experience formula of the non-uniform coefficient Cu and digging up of debris flow:Q2=B2Cu0.237(Q1,Q2are unit width discharge; B1,B2are coefficient; Cu is uniformity coefficient).(5) According to the two single factors and the relationship of forming debris flow required discharge per unit width, fitting out a comprehensive empirical formula in forming debris flow by discharge per unit width relate to the two factors of median particle diameter of d50and non-uniformity coefficient Cu:Q1=C1(Cu0.2d+1), fitting out a comprehensive empirical formula in digging up by discharge per unit width relate to the two factors of median particle diameter of d50and non-uniformity coefficient:Q2=C2(Cu0.2d+1)(Q1,Q2are unit width discharge; Ci,C2are coefficient; Cu is uniformity coefficient; d is relative median diameter).(6) Through the analysis of particle gradation obtained sampling in Niujuan gully and Wenjia gully, using the actual field median diameter d50and non-uniformity coefficient Cu into comprehensive fitting formula to calculate the required discharge per unit width in forming debris flow and digging up, and compared the conclusion with the hydrological calculation value of forming debris flow in Niujuan gully and Wenjia gully, it shows that the fitting formula can reflect the influence to the clastic flows of median particle diameter of d50and non-uniformity coefficient Cu. Although the formul has discrepancy with hydrologic computation, but it has the same trend and has certain applicability and reference.