Research On Intermediate Particles And Yield Stress Of Debris Flow By Experiments

Siltation of debris flow to buildings and engineering facilities is one of the main hazards of debris flow disaster,silting not only seriously threatens the safety of human life and property,but also restricts the development of social economy.Siltation thickness of debris flow is one of the most important parameters of debris flow,and it is also an important parameter for debris flow disaster assessment and prevention.Therefore,studying the silting thickness of debris flow is not only helpful for us to better grasp the characteristics of debris flow movement,but also helpful for us to carry out effective debris flow disaster control.The deposition thickness is obtained mainly through field investigation and parameter calculation.In parameter calculation,the yield stress of debris flow is closely related to the maximum deposition thickness of debris flow.At present,researches on influencing factors of debris flow yield stress can be divided into three categories:Firstly,only volume concentration of debris flow solids is involved.Secondly,the volume concentration of clay and debris flow solids is considered simultaneously.Third,the effect of bulk density and coarse particle size and shape should be considered.The current studies on influencing factors have their own advantages and disadvantages,but they all have some shortcomings,that is,the influence of the properties of intermediate particles?particle size between 0.005mm and 0.25mm?on the yield stress of debris flow is not considered.Aiming at the shortcomings of the existing research,based on the mechanism of action of coarse particles on the yield stress of debris flow,in this paper,medium particle size and intermediate particle gradation are introduced,through the indoor debris flow circulation trough experiment control variables,explored the influence of intermediate particle size and gradation on the yield stress of debris flow,and qualitatively analyzed the influence of intermediate particle shape on the yield stress of debris flow,the modified and improved numerical model was obtained and verified by combining field survey data and previous experimental data.The conclusions of this paper are as follows:?1?As an important part of the debris flow slurry,the particle has a greater influence on yield stress of debris flow,the influence is mainly reflected in the grain size distribution,particle size,shape and other properties.In this paper,the relationship between intermediate particle size,particle size and yield stress is quantitatively analyzed by making up debris flow slurry with different intermediate particle characteristics and carrying out laboratory flume experiment of controlling variables.?2?Control of intermediate particle size(d₅₀)and shape?sphericity??are the same,by analyzing the experimental data,the farther away the particle gradation parameter—curvature coefficient Cc is from 1,grading the better,that is the particle size is not uniform,and the smaller the yield stress of debris flow;When the particle gradation parameter—curvature coefficient Cc is closer to 1,the worse the gradation is,that is,the particle size in the middle is uniform,the particle composition is single,and the yield stress of debris flow increases.?3?At the same time,it is found that the more uneven the particle combination was,the better the gradation was,the greater the difference between the measured value of the intermediate particle experiment and the coarse particle research curve was,while the more uniform the particle combination was,the worse the gradation was,the closer the measured value of the intermediate particle experiment was to the coarse particle research curve.?4?Control the intermediate particle size distribution?curvature coefficient Cc?and shape?sphericity??are the same,by analyzing the experimental data,when the solid volume concentration of debris flow is less than 0.47,the particle size of almost no effect on yield stress of debris flow;When the solid volume concentration of debris flow is greater than or equal to 0.47,the medium particle size is negatively correlated with the yield stress of debris flow,that is,the smaller the intermediate particle size is,the greater the yield stress is,and the larger the intermediate particle size is,the smaller the yield stress is.?5?The debris flow deposits in three different lithology areas of granite,slate and sandstone are sampled,and particles in the sample of the further subdivided into three kinds of particle size range?0.25mm⁰.10mm?0.10mm⁰.05mm?0.05mm⁰.005mm?,observed under different multiple microscopes,it is concluded that:in the same lithology,the size of the particle size of different will not cause differences in shape,granite and slate area of particles mainly shows polygonal,sandstone region of spherical particles mainly in class;In debris flow samples from three different lithological regions,The parameter of intermediate particulate shape—sphericity roughly follows the rule of?_sandstone>?_slate>?_granite.?6?Based on the study of coarse particles,the volume concentration correction coefficientáwas obtained after the grading and particle size of intermediate particles were modified,the specific expression was:á=1.14n(8.....,where:n is a material constant;Cc is the curvature coefficient of intermediate particles;S is the surface area of the intermediate particulate material of the average unit?mm²?;?is the intermediate spherical particles;The correction coefficient of volume concentration has intermediate particle properties on the influence of the yield stress of debris flow into consideration.?7?After obtaining the correction coefficientáfor the volume concentration of the intermediate particles,the formula for calculating the equivalent volume concentration in the original yield stress calculation model was improved by combining with the correction coefficient a for the volume concentration of the coarse particles obtained by Chen's study,the specific expression was:C=((3(6+?4á?,Where,C is the equivalent volume concentration;C₀ is the initial volume concentration;X is the percentage content ratio of coarse particles to solid parts except fine particles in debris flow;Y is the percentage content ratio of intermediate particles to solid parts except fine particles in debris flow;a is the volume concentration correction coefficient obtained by studying the relationship between coarse particles and yield stress;áis the volume concentration correction coefficient obtained by studying the relationship between intermediate particles and yield stress.In this paper,the model was verified by the experimental data of Marr JG and Coussot,the measured data of Huoshao gully and the field survey data of debris flow gully.The verification results also confirmed that the new model is more scientific and reliable than the coarse particle model after considering the influence of intermediate particle properties.