The Diffusion Mechanism Of Rock-fall Impact Force

Rockfall impact is the main load for designing the passive protection structures.Rockfall protective structures often have a thick layer.The thickness of the cushioning will affect the impact force of rockfall to a certain extent.The rockfall impact force transmit to the protective structure through the diffusion of the cushion.Therefore,the diffusionof the impact force in the cushion plays a crucial role in the design of the protective structure.At present,there are relatively few researches on the diffusion mechanism of rockfall impact.Based on this,this paper has studied the rockfall shape,gravel soil cushion,compaction degree and pad under the support of the National Natural Science Foundation of China(51408084)through model tests.The effect of layer thickness on the impact diffusion of rockfall,and through the change of the interparticle force chains in the PFC discrete element program,reveals the impact diffusion mechanism of rockfall under different impact conditions,the diffusion range of rockfall impact force,and the diffusion angle.The results of the study are as follows:(1)In this paper,the effect of rockfall shape on the impact diffusion is studied through model tests.The contact between the ballstone and the cushion is defined as the surface contact,and the contact form between the block,the column and the cube and the cushion is defined as the plane contact.Among them,the impact of the ball rock on the protective structure is the weakest,and the impact force has the largest range of diffusion.The results show that the surface contact impact force is more likely to diverge;when the rockfall and the cushion are in plane contact,the impact force is relatively concentrated.For 2kg of rockfall,the acceleration at the midpoint of the plane contact plate is 1.12 to 2.34 times that of the surface contact action.(2)The influence of the gravel content of the cushion on the impact force and the diffusion range of the rockfall was analyzed.The study shows that the gravel content of the cushion has a greater impact on the impact strength of the rockfall.With the increase of the gravel content,the impact strength of the rockfall is greater;however,the gravel content of the cushion has less impact on the impact of the rockfall.When the gravel content is below 50%,the impact force increase is below 50%;when the gravel content is 75%,the impact force increases between 80% and 110%.When the falling stones of different qualities fall from a height of 3m,the acceleration at the midpoint of the gravel cushion plate is 1.04 to 1.52 times that of the soil cushion.(3)The effect of cushion density on rockfall impact force and its diffusion range is analyzed,which shows that the cushion density has a great influence on the impact of rockfall impact force.When the density is small,the rockfall impact force appears stress concentration phenomenon,otherwise stress occurs.Diffusion phenomenon.When the falling height of the falling rock is 1m and it is pressed with 35.7kg weight,the acceleration at the midpoint of the concrete slab is 1.13 to 1.37 times that of natural accumulation;when using 71.4kg weight for real-time pressing,the acceleration at the midpoint of the concrete slab is Naturally accumulated 1.25~1.49 times.(4)The effect of cushion thickness on the impact force of rockfall and its diffusion range was analyzed.It was found that the thickness of cushion had a significant impact on the diffusion range of rockfall impact force.The greater the cushion thickness,the wider the range of rockfall impact force diffusion.When the cushion thickness just begins to increase,the diffusion range of the rockfall impact force increases significantly,but as the thickness increases,the impact force diffusion range does not increase significantly,and the buffer effect on the impact force of the rockfall is not increased when the thickness of the cushion layer just begins to increase.So obvious.(5)The influence of rockfall radius,lithology and landing height on rockfall impact force and diffusion range was analyzed.The results show that the falling height of the falling rock and the falling height of the falling rock have large impact on the impact of rockfall and the impact force,while the lithology has little impact on the rockfall impact force and impact force diffusion.With the increase of the drop height and radius,the rockfall impact force and the impact force diffusion range increase.(6)When the same impact energy is analyzed,with the increase of the impact angle of the rockfall,the impact force of the rockfall also gradually increases.When the impact is met,the impact of the rockfall has the largest diffusion range.When the collision occurs,the diffusion direction is the same as the direction of the impact force,and the impact force of the rockfall changes little when the collision occurs.When the impact angle is 45°,the diffusion range of the impact force is 1.01 times that of 30°;when the impact angle is 60°,the diffusion range of the impact force is 1.02 times that of 30°;when the impact angle is 75°,the impact force The diffusion range is 1.06 times that of 30°;when the impact angle is 90°,the diffusion range of the impact force is 1.77 times that of 30°.(7)The range of the impact diffusion angle of rockfall was obtained through numerical simulation.The simulation results of PFC2 D show that the impact diffusion angle is between 26° and 43°.It shows that under the same impact conditions,the stronger the impact,the greater the diffusion angle;and the diffusion angles of the impact force of rockfall of different thicknesses are all in the 36° fluctuates.