Research On Dynamic Response Of The Shed-tunnel Structure Under Rockfall Impact

With the rapid development of China's economy and the exploitation of mineral resources in the west,a large number of steep rock slopes occur in mountainous areas,resulting in frequent rockfall disasters.The rockfall hazard has seriously affected the traffic safety and harmed the safety of life and property.Therefore,it is necessary to systematically study the impact effect of rockfall.In this dissertation,the existing formulae for calculating the impact force of rockfall were summarized and the differences among the formulae were compared and analyzed.The influence of rockfall characteristics on impact effect was analyzed systematically,and the influence of cushion thickness and material on the impact resistance of shed tunnels was further discussed.The main contents are as follows.(1)The existing formulae of impact force were summarized and a brief comparative analysis was given.The results show that the maximum impact force obtained by representative calculation methods increases with the mass and falling height of the rockfall.The difference of the maximum impact force calculated by different methods can be up to 6-7 times.(2)The influence of rockfall characteristics on impact effect was analyzed systematically by ANSYS/LS-DYNA code.The following conclusions were presented:(1)with the increase in rockfall mass,the impact force,impact time,penetration depth and equivalent dynamic stress of the shed-tunnel structure all increase linearly.(2)with the increase in falling height,the impact force,penetration depth,equivalent dynamic stress of the shed-tunnel structure and the acceleration of rock all gradually increase,but the impact time is less affected.(3)the impact force,penetration depth and the acceleration of rock in normal vector all increase with the impact angle.If the impact angle is less than 45 degree,the impact force,penetration depth and the acceleration of rock in tangential vector all increase with the impact angle,while when the impact angle is greater than 45 degree,the opposite is true.(4)when the shape of the rock blocks is cuboid and cube respectively,the maximum impact force is about 6-7 times that of the sphere.(3)With the increase in cushion thickness,the impact force of rockfall and the deflection and equivalent dynamic stress of the shed-tunnel structure all decrease continuously,while the decreasing trend becomes weaker.It has little effect on the penetration depth and kinetic energy consumption by changing the thickness of cushion,when the cushion thickness is greater than the penetration depth.(4)The EPS light-weight soil can effectively reduce the impact force of rockfall and the deflection and equivalent dynamic stress of the shed-tunnel structure.It shows that EPS light-weight soil has a good energy consumption effect and can better protect the shed structure.However,the EPS light-weight soil will produce larger plastic deformation after the impact of rockfall.The material of cushion is prone to failure when the shed –tunnel structure is often subjected to rockfall hazards.In this case,the sand cushion with strong resistance to deformation is recommended.