Study On The Grain-size Distribution For Initiation And Catastrophe Mechanism Of Slag-type Debris Flow

In some cliffy landforms and loose terranes of hill and mountainous areas,as a result of large-scale concentrated mining of mineral resources,a large number of mining residues are accumulated in ditches.It not only increases the longitudinal slope,but also provides sufficient sufficient source for the generation of debris flow,this leads to frequent occurrence of slag-type debris flow disaster and inestimable loss.There are many factors affecting the initiation of debris flow,such as grain-size distribution,bed slope,critical water content,etc.Because of the complex lithology of the mine and the different grain-size distribution,the characteristics of debris flow formation and movement are quite different,and the catastrophe mechanism is also different.Therefore,through studying the grain-size distribution effect of initiation mechanism of slag-type debris flow and it's catastrophe mechanism,can not only promote the theoretical development of debris flow initiation,but also has important significance for the early warning and prevention of debris flow in mining areas.In this dissertation,Tongyu slag-type debris flow in Tongguan Gold Mining Area of Shaanxi province is taken as the research object.Based on data collection,analysis and field investigation,the basic characteristics of slag-type debris flow in this area are summarized.Through laboratory tests,the physical and mechanical properties of slag in debris flow source area are analyzed.Based on the Particle Flow Code software,initiation process of four numerical models of slag-type debris flows with different grain-size distribution under rainstorm saturation conditions is simulated,analysis of the effect of grain-size distribution on the initiation of slag-type debris flow and it's catastrophe mechanism.The main research results are as follows:(1)90%of the debris flow material sources in the study area come from slag,most of which belong to unplanned random stacking,dumping along the slope around the mine,and the accumulated slag seriously blocked the channel.Through calculation,it can be concluded that the average unit weight of debris flow fluids in each branch gully is 1.502~1.697 t/m~3,the average velocity of cross section is 6.13~7.18 m/s,the peak discharge value of rainstorm flood is 0.81~5.64 m~3/s,the peak flow of debris flow is 1.32~11.62m~3/s,the total flow volume of a debris flow is 239.16~2113.31m~3,the total amount of solid material washed out by a debris flow is 115.55~1234.66 m~3.(2)The laboratory tests results of physical and mechanical properties of slag in debris flow provenance area show that the variation of permeability and shear strength with grain-size distribution:When the content of fine particles in slag is high,the permeability coefficient decreases with the increase of sludge content.When the content of fine particles is low,the permeability coefficient increases with the increase of curvature coefficient and equivalent particle size.The shear strength of slag decreases with the increase of fine particle content.(3)The results of numerical simulation show that:Slag-type debris flow often presents the characteristics of stratification and fragmentation when it starts.And start at the foot of the slope ahead of other positions.The formation process of debris flow can be divided into two stages:secondary accumulation of slag and flow siltation.There is a grain-size distribution which is most favorable for the initiation of slag debris flow,when the content of fine particles is too high or too low,it is not conducive to the initiation of debris flow.Although debris flow with low content of fine particles is difficult to start,it has a high speed after starting,and it completes the process in a shorter time.(4)The failure mode of debris flow with high fine particle content at start-up is mainly roof-cutting caused by seepage,the form of motion is extrusion sliding.The main failure mode of debris flow with low fine particle content at start-up is internal erosion caused by scouring,the form of movement is falling and topping.