| China is a country with an area of 9.6 million square kilometers.Due to its vast territory,China's geological environmental conditions are very complicated with many hills and mountains.Therefore,this also leads to relatively frequent geological disasters,and the disaster situation is relatively serious.According to statistics from the China Geological Survey,there are more than 200,000 hidden geological hazards across the China.A large number of geological disasters have greatly adversely affected people's lives and property safety and social stability.Therefore,it is of great significance to study the mechanism of geological disasters and use them as a basis to promote disaster prevention and reduction.However,the rock avalanches is extremely sudden,and because of its instantaneousness,suddenness,and concealment,it is not realistic to directly observe the occurrence of the rock avalanches.Therefore,the analysis of the congeries is the breakthrough of the Rock avalanche research,and the analysis of the particle size is an important breakthrough direction of the Rock avalanche research.In this paper,the statistics of the particle size distribution of the congeries has gone through: on-site screening ? artificial statistics on aerial images of congeries ? aerial photography of drones-Drone aerial photography-PCAS recognition.Finally,through the mutual verification and detection of three methods,it was found that the "Drone aerial photography—PCAS particle size identification" is the most convenient and fast statistical method on the basis of ensuring accuracy.In order to verify the " bimodal distribution " and " inverse grading " of the congeries,and to analyze the dynamic characteristics of the rock avalanches,indoor rock avalanches chute tests with different particle size ratios were performed in this study.In addition,due to the impact of internal particle collisions,the long runout of rock avalanche in different particle size gradations are different.The rock avalanche distance corresponding to the gradation can be obtained through the indoor rock avalanche chute test of various gradations.The relationship between the rock avalanche distance and the particle gradation can be obtained through dimensional analysis.After field investigation and indoor particle size statistical analysis of the congeries of Xinmocun landslide,Pusacun collapse,two Baigecun landslide and Shuicheng landslide,combined with the particle size distribution and movement process analysis of the indoor chute test,the following conclusions can be drawn:?1?The particle size distribution of the four rock avalanche congeries were counted by three methods: field screening,artificial visual statistics,and PCAS statistics.The various statistical results are mutually verified,and it is concluded that it is feasible to use PCAS statistical method to identify the particle size of the congeries.?2?It can be seen from the statistical results of the congeries that they have obvious "bimodal distribution" phenomenon and "inverse grading" accumulation phenomenon.?3?Regarding the phenomenon of "inverse grading" of congeries,this article explained it with "Brazil nut effect" and Bagnold experiment.?4?In this paper,through the analysis of the force of the particles,the "bimodal distribution" accumulation phenomenon is deeply analyzed.?5?The "bimodal distribution" phenomenon and "inverse grading" phenomenon of rock avalanche congeries were verified by the debris flow chute test on the 30 ° slope.?6?Through the chute test,the relationship between the distance of movement and the equivalent particle size is obtained through dimensional analysis:L=31.623·?0.002991d'/B?0.1042?tan??0.663?VH?0.25,The formula is verified by statistical examples of landslides,and the accuracy of the formula is good.?7?Combined with the movement process of the rock avalanche recorded by the chute test,the accumulation mechanism of the "bimodal distribution" phenomenon and "inverse grading" phenomenon of the rock avalanche congeries particles was analyzed.?8?Taking the movement process of the rock avalanche recorded in the chute test as an example,the dynamic characteristics of the particle size distribution of the rock avalanche congeries were analyzed,furthermore,the "bimodal distribution" phenomenon and "inverse grading" phenomenon of the rock avalanche congeries were explained by the direction of kinetics.?9?The movement process photos recorded by the high-speed camera can be quantified by the MATLAB software for the velocity of the rock avalanche,and it can be obtained that the speed also has a "bimodal distribution" phenomenon,which corresponds to the "bimodal distribution" phenomenon of the particle size of the congeries.?10?Record the debris flow chute test process with a high-speed camera and use the PIVlab module in MATLAB software to quantify the speed.It can be seen that there is also a " bimodal distribution " phenomenon in the velocity of rock avalanche,which corresponds to the " bimodal distribution " phenomenon of the particle size of the congeries.Then,the calculation result of the chute test speed is also another verification of the formula of particle size accumulation speed: u0=A·[?k]1/2·d2.?11?During the flow of rock avalanche particles,due to the poor roundness of the particles,the energy consumed by the rolling flow to overcome rolling friction is often too much.This leads to a reduced ability of the rock avalanche to carry large expectations.The fractal dimension of the roundness of the rock avalanche is calculated in this paper.The statistical results of roundness also show a good "bimodal distribution " phenomenon,which corresponds to the " bimodal distribution " phenomenon of the congeries. |
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