| The Karakoram highway is the merely land transportation route leading to the South Asia Subcontinent and the Middle East,its economic,political and strategic position is self-evident.The Gaizi section of Karakoram highway is an requisite part of the Karakoram highway,located in the hinterland of the West Kunlun Mountains,the natural environment is extremely bad,the debris flow disasters along the road,which seriously affect the normal operation of the highway,and the national"The Belt and Road"initiative,the capacity of the road to put debris flow disasters along the highway are urgently needed for effective prevention.At present,the formation mechanism of debris flow is not clear in this area,especially the large gully-type debris flow,it is difficult to put forward reasonable and effective project management plan.Therefore,it is necessary to study the formation mechanism of debris flow along the gully to provide theoretical support for the prediction and major engineering of debris flow.This paper takes the Gaizi section of Karakoram highway as the research object.First of all,through data collection and field investigation,it preliminarily probes into the types,distribution and genesis of debris flow in the Gaizi reach of the highway,and puts forward the characteristics of typical gully debris flow along the highway.Secondly,based on the indoor test,osmotic test and shear test,the structure and physical mechanics characteristics of the soil of moraine soil and debris flow gully are analyzed.Finally,based on the artificial water scour test,the paper emphatically studies the formation mechanism of the glacier gully and rain-gully debris flow,and takes into account the influence of the flow rate,the water concentration and the initial moisture content of the soil on the start of the debris flow,and preliminarily reveals the mobility mechanism of different types of debris flow,the following conclusions are mainly drawn:1.Along the road debris flow has a total development of 98,with the highway and directly affect the road debris flow 53,including rainfall debris flow 26,glacier debris flow 27.Rainfall-triggered debris flow is esay to be formed by rainfall excitation every May-September in Oita to Gaizi village,and June-August glacier mass ablation prone to glacier debris flow in Gaizi village to the Bulungkol section.Based on the analysis of the formation conditions of typical gully debris flow,it is preliminarily revealed that the rainfall-triggered debris flow takes the channel loose material as the source supply,the starting mode is the scour-start type,the glacier debris flow source is mainly moraine soil,and the starting mode is mainly the scour starting type and the blockage type.2.By the experiment of the C_u=41.8～66.09,the non-uniform coefficient is obtained and the curvature coefficient is C_c=0.48～0.54,the coarse particle distribution is uneven,for the poor gradation gravel soil;through the direct shear test of moraine soil,it is found that the cohesion force and internal friction angle decrease with the increase of water content,and the increase of fine grain content increases first and then decreases,and the shear strength index is the highest when the fine grain content 10%～30%,through the infiltration test of the moraine soil,it is found that the permeability coefficient decreases with the increase of fine particle content,and the negative exponential relationship between the two,with the increase in water content is the trend of the first descent,the overall trend is"V"font,the water content is 15%when the permeability of moraine soil is the worst.3.After the gully soil test,obtained its non-uniform coefficient C_u=9.75～35.77,curvature coefficient C_c=1.13～2.58,for graded good gravel soil.Through the direct shear test of the debris flow channel soil,it is found that the cohesion force and internal friction angle are decreasing with the increase of water content,with the increase of fine grain content,the trend of first ascending and descending was decreased.And the permeability coefficient was first rising to the peak after the increase of water content,and the permeability was the best when water content was 15%.4.On the basis of conducting flume experiment,in order to study the initiation mechanism of debris flow in different water yields.The results indicate that migration of fine sand particles inside moraine soil causes the formation of seepage channel under the action of seepage erosion,and the change of internal structure and pore water pressure increase lead to frame collapse in the front edge,and further a small debris flow is triggered.Under the effect of continuous water scouring,the super surface of saturation moraine soil is scraped into a gully by headward erosion,and local channel blockage happens during down cutting and lateral erosion,further a larger scale debris flow occurs due to outburst.It is preliminarily speculated that the starting critical melting water of debris flow is 12-16l/min under the condition of 25°slope,and the triggering process of glacial-meltwater induced debris flows can be divided into four stages,and the initiation mechanism is summarized to infiltrating saturation,seepage erosion,frame collapse and scouring initiation.5.Based on water scouring test,the starter of debris flow in gully soils were studied by selecting 4 groups of slurry concentration,3 soil initial moisture content and 3 flow rate.The results show that under the action of different concentration slurry,Slurry concentration 5%has strong sediment transport capacity,it is easy to start the formation of debris flow,and low concentration mud(clear water)a large number of surface fine particles scouring the formation of water and stone flow,high concentration of mud(10%-15%)limit and constrain particle movement,reduce the possibility of debris flow starting,it is thought that the reason of the difference is that the internal structure and the force of the soil are changed by the slurry adsorbed on the soil body.The initial water content of soil affects the infiltration rate of water flow and the strength of soil,which causes the single particle slippery destruction of the soil under the low initial water content,and the large-scale collapse failure under the high initial water cut rate. |
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