Study On The Long-runout Distance Of Rock Avalanche

Rock avalanches are giant landslides that travel kilometers within minutes.For studying the long runout of rock avalanches,the main factors affecting the long runout distance are determined based on the sites investigation and statistics of typical disaster,firstly.And then equipped with a PVC chute,and a metal chute working under enhanced gravity acceleration controlled by computer,designed by author,series of granular flow and deposit experiments were carried out:chute deposit experiment under different water content conditions,chute deposit experiment under different particle sizes,chute deposit experiment under high centrifugal acceleration conditions.In these studies,observations for mobility of granular flow are realized with abundant of data on long runout distance and deposit characteristics.And the influence of environmental gravity acceleration on movement distance under varying physical characteristic are explored.At last,a calculation model for rock avalanche travel distance was established,based on physical quantities such as volume,height difference,particle size and basal friction coeff-icient.The main conclusions of this paper are as follows:(1)The mobility from well-known rock avalanche in China and abroad,was used to analyze the influence of the volume(V),the width of the middle of the slip zone(Wm),vertical elevation difference between the peak of the landslide and the front edge of the landslide accumulation body(Hmax),Sliding surface inclination of sliding source area(P)and Slope of the middle of slip area(y)on the long runout of rock avalanche,The analysis results show that the vertical elevation difference between the peak of the landslide and the front edge of the landslide accumulation body(Hmax)has the greatest effects on the maximum long runout,and the landslide volume(V)is the factor that has the second largest influence on the maximum long runout,and then the landslide width is the third factor that influences the long-distance motion characteristics,followed by the Slope of the middle of slip area,and the influence of the Sliding surface inclination of sliding source area is the smallest among the analyzed factors.(2)The relationship between the water content of debris and the horizontal displacement obtained by the chute test shows that the horizontal displacement gradually decreases with the increase of the moisture content under the condition that the weight of quartz sand is unchanged;After the water content reaches a certain value,the horizontal displacement of the rock avalanche begins to increase rapidly.There is a moisture content threshold between the reduction and increase of the displacement of the rock avalanche,which is the limit value of the rock avalanche and the debris flow.The moisture content threshold interval is 0.12?0.18,corresponding to a solid mass volume concentration of 0.67?0.75;And the bulk density interval of 2.15 t/m3 to 2.30 t/m3.The liquid bridge plays an important role in the connection state between the rock avalanche particles and affects the macroscopic movement state of the rock avalanche.(3)According to dimensional analysis and model test,a formula for long runout based on the width of the slip zone(B),particle size of the rock avalanche(d)and the ramp angle(a)is constructed:(?)a formula for movement distance based on the width of the slip zone(B),particle size of the rock avalanche(d),the ramp angle(a)and friction coefficient of sliding surface(?)is constructed:(?)Soil rock avalanche are not suitable for this model because there is no maximum particle size(d)parameter.At the same time,this model cannot be used to estimate the movement distance of glacial-rock avalanche.(4)By carrying out simulation experiments of rock avalanche,combined with on-site investigations and aerial photography of UAVs,the distribution of large-diameter blocks in the rock avalanche accumulation was studied,and it is considered that the accumulation area not only has a inverse grading structure in the depth direction but also has a double peak shape in the distribution of large grains in the slip direction.(5)The relationship between long runout and gravitational acceleration of rock avalanche is discussed in three ways,Among them:? Using the formula calculation method,it is found that when the rock avalanche is considered as a whole stream,L and g are linearly proportional;When the rock avalanche is considered as a boundary layer flow,the relationship between L and g is an exponential function and the index is 5/6.?Through statistics,it was found that when the Earth's rock avalanche data is replaced with Martian rock avalanche data,then compares with the Martian rock avalanche data,we obtained ??1.0046,approximate to 1.When the Earth's rock avalanche data is replaced with terrestrial non-pyroclastic flow data,we can get ??0.3373,which is approximately 1/3.?In the geotechnical centrifuge test,the relationship between L and g was found in two phases:Bump up phase and steady change phase.When the centrifugal acceleration exceeds 10g,the movement distance of the rock avalanche is basically stable,and its variation range is only about 5cm.In other words,once the centrifugal acceleration exceeds 10g,the change of the centrifugal acceleration will not change the movement distance of the rock avalanche significantly.