Study On High-speed And Long-distance Landslide Debris Flow Migration Process In Karst Mountainous Area

High-speed long-distance avalanche-clastic flow refers to a long-distance movement process similar to fluid state in the form of fast debris flow after large-scale rock mass instability on a high and steep slope.In this paper,based on the on-site investigation and analysis of the long-distance landslide-clastic flow disaster point of Guanling Dazhai highway in Anshun City,Guizhou Province,using the slope chute physical model test as the research means,different height,different particle size ratio of landslide-clastic flow are studied,and the rules of particle velocity and migration distance of clastic flow with different height and different particle size ratio are obtained.The numerical model of 1:1 with the physical model of slope chute is established by PFC,and the simulated distance is consistent with the actual moving distance.The PFC three-dimensional discrete element numerical simulation analysis of Guanling Dazhai landslide is carried out to study the law of high-speed long-distance landslide-clastic flow movement in karst mountain area.The main research results are as follows:(1)through the debris flow chute test,under the condition of the same height,slope angle,quality and sliding surface material,according to the same particle size ratio(7:3),the migration distance of landslides uniformly mixed with different particle sizes is basically the same,and the migration range is also roughly the same.The results show that any combination of particles with the same particle size ratio has no effect on the movement distance in the process of gliding motion.The accumulation of stop movement accords with the phenomenon of anti-sequence accumulation,which indicates that the debris flow has the function of separation in the process of movement,and there is energy consumption in the process of separation.Under the condition of particle mixing,the migration distance of debris flow is the smallest.(2)under the condition of the same height,through the comparative analysis of the decline of single particle size and mixed particle size,the sliding body with single particle size of the same mass moves farther than the sliding body with mixed particle size ratio.The results show that the existence of small particles will hinder the movement of the whole,and a single particle size is beneficial to maintain the motion inertia and reduce the friction energy consumption.The farthest movement distance of single particle size is calculated by the formula,and the farthest migration distance of single particle size obtained by the experiment is basically consistent with the theoretical value calculated by the formula.(3)when selecting three different heights of 2m,1.5m and 1m,under the condition of fixed slope angle of 30 °,the mixed particle size and single particle size of the same mass decrease,and the velocity curve trend diagram is roughly the same.Through the comparative analysis of three kinds of height decline speed,it is found that it takes the least time for each group to reach the maximum speed at 1 m,and all reach the maximum speed at about 1.5 s,indicating that the time to reach the maximum speed is greatly affected by height.Height is the main factor affecting the maximum migration speed.(4)A numerical model is established for the physical model test of the slope chute.The ratio of the model to the prototype is 1 to 1,and the selected spherical particles are 100mm?200mm and 200 mm to 300 mm.According to the same particle size ratio as in the actual model test,that is,the ratio of large particles to small particles is 7 to 3,the final motion distance is consistent by adjusting the friction coefficient between the acceleration zone and the accumulation zone,and the motion model is simulated which is consistent with the motion distance of the actual clastic flow particles.It is of certain significance to study the scope of disaster.(5)PFC3D can well invert the whole process of movement and diffusion of long-distance landslide-clastic flow from start-up to accumulation in Guanling highway.The whole movement lasted about 200 seconds,and reached Yongwo Village Group about 20 seconds after starting.it strongly collided with the hilltop of Yongwo Village formation,and the speed reached the maximum value of 51.82 m pound s.After the impact,the speed began to decrease rapidly,and decreased slowly at about 160 s,to about 200 s,the speed was 0.Through the analysis of the simulation results,it is found that the PFC3 D particle flow program can better simulate the three-dimensional accumulation shape and influence range under the condition of selecting reasonable parameters,which can provide a reference for delineating the safe avoidance range.