Study On Fragmentating-related Movement And Deposition Characteristics Of Rockfall

Rockfall is a common mountainous geological disaster,which has the characteristics of high frequency,strong randomness,and high suddenness.It occurs universally all over the world.Rockfall seriously threatens the lives and property of mountain residents and traffic safety.Fragmentation can change the propagation of rockfall,which in turn affects the hazard range of rockfall.However,the current researches rarely involve the fragmentation phenomenon in the rockfall and the mechanism of fragmentation on the movement path and deposit of the rockfall.Therefore,taking rockfall as the research object,this paper adopts laboratory experiment and DEM,focuses on the fragmentation process and characteristics,and explores the propagation characteristics,fragmentation characteristics and deposit features of fragmented rockfall under the conditions of the the block strength,block shape,falling height,movement distance along the slope,slope angle,analysis of rockfall propagation,fragmentation and deposit laws under different initial conditions,reveals the fragmented rockfall propagation and deposit mechanism.The main conclusions of this research are as follows:(1)Fragmented rockfall has the characteristics of regional deposit.The small particle size fragments and powders produced by fragmentation are mainly accumulated near the turning point between the slope and the bottom surface,and the deposit area is large and continuous(the blocks contact with each other densely).When the larger particle size produced by fragmentation deposit,the discreteness is strong,and there is no continuous deposit phenomenon in the motion path.The greater the falling height,the greater the movement distance along the slope,the greater the angle of the slope,the greater the difference between the length and height in the shape of the block,and the more obvious the regional deposit characteristics.(2)Block strength,falling height,moving distance along slope,block shape,slope angle significantly affect the propagation and deposit characteristics of fragmented rockfall.As the falling height and the distance of movement along the slope increase,the deposit range S,the farthest movement distance L_r,and the center of gravity movement distance L_gincrease;with the increase of strength,S decreases;The greater the difference between the length and the height of the block shape,the greater the S and L_r,and the smaller the L_g;as the slope angle increases,the L_g tends to decrease,and S tends to increase.(3)Block strength,falling height,movement distance along the slope,block shape,and slope angle significantly affect the degree of rockfall fragmentation.As the strength decreases,the falling height increases,and the distance of movement along the slope increases,the degree of rockfall fragmentation increases;the greater the difference between the length and the height in block shape,the greater the degree of fragmentation;With the increase of the slope angle,the fragmentation degree of rockfall generally increase,but,when the slope angle is 75°,the degree of block fragmentation is lower than that of the slope angle of 60°.This is mainly due to the action of this steep slope,the rockfall at the turning point due to the fragmentation movement to form a buffer layer,thus weakening the degree of fragmentation.(4)The block shape significantly affects the fragmentation form and process of the rockfall.The relatively large aspect ratio in the block shape is mainly caused by the movement along the slope.The block breaking is mainly caused by the tensile effect,and the direction of the cracks is mainly approximately parallel or approximately perpendicular to the direction of movement.The fragmentation of blocks with relatively small aspect ratio in the block shape is more serious at the turning point.During the slope movement,the block fragmentation is mainly caused by shearing,and the direction of the cracks is mainly oblique to the impact point.(5)Fragmentation helps increase the range of rockfall deposit.Through the comparative analysis of the relationship between the fragmentation degree and the deposit range of rockfall under the conditions of block strength,falling height,movement distance along slope,block shape and slope angle,it is found that the greater the fragmentation degree of rockfall is,the larger the deposit range is as a whole,which is mainly due to the regional accumulation phenomenon in the fragmentation movement of rockfall.