Constraint Mechanism Of High-frequency,Small-medium-Sized And Low Carrying Capacity Of Xiao River Debris Flow

The debris flow has become one of the most serious natural disasters in the world.For example,in Xiao River,Yunnan,which has always been known as the "Nature Museum",and debris flows occur frequently.These frequent debris flows have caused the formation of Xiao River barrier lakes and roads to the region.Bridges and other transportation facilities and farm houses and people caused serious damage and huge economic losses.Due to its typical exposed rocks,complex geological tectonic activities,special geomorphic forms,and complex mutual feedback with natural geographical conditions,Xiao River has frequent debris flows and complete types.It is an important material,so it has been highly concerned by scholars at home and abroad and has become one of the most favored sites for debris flow researchers.However,the current research results on the Xiao River debris flow are mainly concentrated on a single factor or boundary conditions such as its formation,migration and deposition.There are few cross-scale studies on the system of its formation.Therefore,in this paper,through the macro-factors such as the natural geographical conditions,landforms,typical special rocks exposed in Xiao River,the overall distribution direction of the earth's in-situ stress in China,and the complex geological structure in the study area,the density and rheological characteristics of the reconstructed debris flow in the laboratory were tested.The system's cross-scale research method has a scientific understanding of the Xiao River debris flow.The constraint mechanism of physical characteristics such as high frequency,small and medium size,and low carrying capacity of Xiao River debris flow is clarified.The research results can further enhance people's understanding of the mechanism of Xiao River debris flow,and provide theoretical guidance for the early warning and prevention of similar debris flows,which has important theoretical and practical significance.Based on the main research content of this article,the following main conclusions are drawn:(1)The study area is affected by the southwest summer monsoon climate.Its rainfall is mainly concentrated in May to October each year and accounts for about 80% of the annual rainfall.At the same time,extreme weather has a significant impact on the study area.Therefore,the natural geographical conditions of the study area made Xiao River provide conditions for the occurrence of debris flow in terms of rainfall,temperature,and humidity.(2)The strata exposed in Xiao River are relatively complete.The earliest is Cambrian and the latest is Quaternary.Typical representative rocks are slate,phyllite,shale,dolomite,sandstone,and mudstone.Among them,slabs Rock,phyllite and shale are brittle rocks,of which slate accounts for more than 80%.XRD analysis shows that the main rock-forming minerals are illite,plagioclase,quartz,and chlorite,all of which are clay minerals and have the physical characteristics of swelling with water.At the same time,the rocks exposed in the study area have the characteristics of softening and accelerating differentiation in contact with water,combined with the climatic conditions of dry and wet alternation and concentrated rainfall in the study area.It shows that the results of the above climate impact factors have a close feedback with the softening and further differentiation of rocks.Therefore,it is proved that the exposed rocks in the study area provide rich source materials for the occurrence and migration of debris flow and the close relationship between them.(3)The direction of the principal stress axis trace of in-situ stress in our country is 106 ° east longitude as the boundary line,and the center of the Qinghai-Tibet Plateau appears to be radiating to the surrounding and distributed to the right from the center.The study area is located on the southeastern edge of the Qinghai-Tibet Plateau and is continuously affected by tectonic activity during the historical period.The Xiao River fault zone that controls the entire study area exhibits the law of left-hand movement.Through field investigations,the occurrence of rock strata in the local area is greatly changed and the characteristics of regional occurrence are obvious,such as approximately horizontal and vertical distribution in the study area.This also shows that the complex geological tectonic activities that are still active at the current stage in the historical period have become the controlling factors for rock fragmentation,slope stability,and accelerated further evolution of landforms in the study area.Thus close relationship between the complex tectonic movements in the study area and physical characteristics of debris flow is obvious.(4)The Xiao River is controlled by the Jinsha River erosion datum,so the down-cutting effect of the Xiao River has been continuing,that is,the influence on the geomorphological evolution of the Xiao River will continue.At the same time,Xiao River was affected and controlled by complicated tectonic movements that are still active,forming the two sides of Xiao River with a maximum altitude of about 3800 m and a minimum of about 1400 m.The difference in altitude between the highest and lowest altitudes is 2400 m,which indicates that the altitude difference in the Xiao River results in the formation of a larger slope body in the River Basin.This landform feature provides sufficient conditions for the transformation of gravity potential energy,so the landform morphology in the study area has a significant causal relationship with the debris flow that occurs.(5)Taking the debris flow of the Nujiang Dong Yue Ge in the typical alpine long-distance non-glacial Nujiang River as a reference object to characterize the physical characteristics of the Xiao River debris flow.By comparing the maximum upper limit particle size of each reconstructed debris flow in Xiao River and Nujiang Dongyue with a diameter of 2 mm,the minimum density of Xiao River debris flow is 1.610 kg / cm3,the maximum is 1.950 kg / cm3,and the minimum debris flow in Nujiang is 1.702 kg / cm3,the maximum is 2.045 kg / cm3.It shows that the Xiao River debris flow has the characteristics of low density.Discuss and analyze the difference in peak pore water pressure under the constraints again: the averages are 0.755 and 0.813,respectively.Through discussion and analysis of the regularity and difference from yield stresses of Xiao River and Nu River Dongyue reconstruction debris flows,the average yield stresses of Xiao River and Nujiang Dongyue debris flows are 30.665 Pa and 68.422 Pa,respectively,which illustrates that the rheological characteristics of Xiao River debris flow.The average value is lower than the reconstructed debris flow of the Nu River.It shows that the Xiao River debris flow has the important physical characteristic of low carrying capacity.