Study On The Computational Method Of Rockfall Impact Force

This paper mainly based on model test and numerical simulation method,studied the rockfall impact force and rockfall impact duration with the variation of the rockfall(rockfall quality,rockfall shape,rockfall falling height)factors and cushion factors(cushion type,thickness of cushion,cushion compaction degrees).Based on the theorem of impulse,establish the calculation model of rockfall impact force.Using the test results of the model fitting a rockfall impact force calculating formula.The main research contents and results are as follows:1.Model test study on the influence factors and change law of rockfall impact forceRockfall factors.Rockfall impact force increases with the increase of rock mass,the impact force increases with the increase of the falling height of rockfall.Positive correlation between the two.The shape of a cube,rockfall impact force,the second smallest cuboid,sphere.The thickness of cushion.Cushion thickness and impact force was negatively correlated,with the increase of the thickness of cushion,rockfall impact force is reduced,but trend of rockfall impact force is reduced is getting weaker.Theoretically,cushion thickness increase is conducive to rockfall impact force decreases,but also increases the gravity of the structure of the door itself.Consideration should be given to implement the drop height and the diameter of rockfall.Cushion compaction factor.Density of impact force size had a significant impact,rockfall impact force with cushion compaction degree increase significantly increased,but with increase of the density,rockfall impact force increase trend gradually slowed down.But with the increase of rockfall impact kinetic energy,because the density of different cushion caused by rockfall impact force will gradually weaken.In engineering practice,do not use the method of stratified rolling to deal with the cushion,but should keep it in a fluffy state,the natural pile.Cushion material factors.For the four different materials composite cushion setting of rockfall impact force,such as rubber plate composite cushion of rockfall impact force,sand cushion cushion composite and geotechnical grille composite cushion in the middle,EPS composite cushion minimum.When the cushion is too thin,rockfall drop impact cushion,cushion cover door structure is compacted,resulting in rockfall and cushion is semi rigid contact,thereby enabling the rockfall impact duration decreases,rockfall impact force increased significantly.The formula is in good agreement with this phenomenon.2.Influence factors and changes the size of the rockfall impact durationRockfall factors and rockfall impact duration decreases with the increase of quality of rockfall,but decreases range is limited,and finally tends to be stable;impact duration decreases with increase in height,and finally tends to be stable;cube rockfall with respect to the cuboid rockfall and sphere of rockfall,impact took small;Cushion factors,impact duration decreases with the increase of the thickness of cushion,and the exponential function relationship;cushion compaction degree of rockfall impact duration significantly affected,with increase of the density,rockfall impact duration decreases.The and tends to be stable;cushion materials of different although hedge strike force influence,but the impact diachronous impact is not obvious,is irregular,the range of variation is small.Appropriate to extend the rockfall impact duration to door structure of shock resistant performance,starting from the factors of cushion can be an appropriate increase of cushion thickness,to try to keep the state fluffy cushion,and available EPS lightweight soil mixed with alternative buffer sand cushion3.Calculation of rockfall impact force(1)based on model test results,the fitting formula of rockfall impact by duration.(2)based on theorem of impulse,consider the rockfall rebound,the gravity and buffer layer thickness,density,material established rockfall impact force calculation formula.The relationship between the maximum impact force and the average impact force is established by using the amplification factor of impact force.(3)the use of rockfall impact force measured back calculate impact test range of magnification coefficient curve.(4)the comparative analysis of the formula and the existing common impact force calculation formula.When the radius to thickness ratio(rockfall diameter and thickness of cushion than)is small,the algorithm results is relatively small;when the radius to thickness ratio(rockfall diameter and cushion thickness ratio is large,the algorithm in this paper is on the high side and increasing trend.4.By using the method of numerical simulation,the full-scale simulation of rockfall drop impact cushion.Comparative analysis of calculation formula of rockfall impact force fitting out.The results show that the rockfall impact duration results show a good agreement with the calculated difference are within 18%.In this paper,the numerical results are compared with the numerical simulation results.Rockfall impact force calculation formula is in good agreement with the numerical results,the difference is within 7%.In this paper,the numerical results are compared with the numerical simulation results.On the whole,the numerical simulation results are in good agreement with the calculation results of the formula presented in this paper,and the trend of the change trend is basically consistent,which shows that the results of the model test are basically credible,and the calculation method is reliable.