Research On Shed Structure For Rockfall Impact

With the support of the National Natural Science Foundation of China(No.51108488),through multi-factor model test including factors such as rockfall shape,mass,height of fall,material and thickness of cushion layer,rockfall impact force and impact duration were analyzed in order to find influence rule.A calculating formula of impact duration was obtained by fitting model test result.The calculating model of rockfall impact force was set up on the basis of impulse theorem.The buffering structure on top of shed for rockfall impact was optimization designed based on the result of model test and the calculating model of rockfall impact force.The main results can be obtained as follows:1.the influence factors and variation rule of rockfall impact force(1)under normal circumstances the impact force of a cube rockfall was the largest one,a cuboid one was the second and the sphere was the least;the impact force was increased with growth of rockfall mass and height by power function;the growth of thickness of cushion layer can lead to obvious decrease of impact force,and can weaken influence degree of rockfall shape;thickness of cushion layer has the optimal value.(2)material of cushion has obvious influence on impact force.(3)rockfall mass and height had positive correlation with impact force,and had the largest influence degree;thickness of cushion layer had negative correlation with impact force,and influence degree was the second;influence degree of shape was the least.(4)actual impact force obtained from model test was better than theoretical calculation result under same condition;theoretical calculation result from now available formula was smaller than actual value,and therefore shed was less safe.2.the influence factors and variation rule of rockfall impact duration(1)under normal circumstances the impact duration of a sphere rockfall was the largest one,a cuboid one was the second and the cube was the least,but difference between these three factors was small;in most cases the impact duration was decreased with growth of rockfall mass and height by approximate linear function;the growth of thickness of cushion layer can lead to obvious increase of impact duration.(2)foam board and rubber sheet cushion layer had the longer impact duration than sand cushion layer on the same condition.(3)thickness of cushion layer had positive correlation with impact duration,and had the largest influence degree;rockfall mass and height had negative correlation with impact force,and influence degree was the second;influence degree of shape was the least.(4)actual impact duration obtained from model test was smaller than theoretical calculation result under same condition,and was more fit with physical truth;the correlation between rockfall mass and impact duration was not consistent with now available formula.3.calculating model of rockfall impact force(1)A calculating formula of impact duration was obtained by fitting model test result.(2)calculating model of rockfall impact force was set up on the basis of impulse theorem and considering rebound,gravity of rockfall and thickness of cushion layer;multiple relationship between the maximum and average of impact force was built by amplification coefficient.(3)amplification coefficient curve was obtained through inverse computation of actual impact force,and low velocity impact of small and fragmentary rockfall can be solved through the curve.4.buffering structure optimization design of shed for rockfall(1)security coefficient of shed should be enhanced under conditions such as existing block shape,large mass or height of fall rockfall.(2)self-gravity of foam board cushion layer was small,and had better buffering effect under certain circumstances.(3)when sand cushion layer was taken as buffering structure,the optimal value should be paid attention.