Study On The Mechanism Of Granular Flow Impact Against Rock Shed And The Buffering Effect Of Cushion Layer

Heavy rainfall or earthquake may induce landslide or collapse.When landslide occurs,it is accompanied by a large number of gravels with different particle sizes,which forms granular flow.With its strong impact force,it causes devastating disasters to structures and people's lives in front of the movement.For many protection structures,rock shed is widely used in the western mountainous area with its advantage of mature technology and good mechanical properties.Generally,the rock shed is used together with cushion layers.However,the particle composition of granular flow is very different,and the structure of the rock shed is various.In previous studies,scholars usually focus on the impact of the cushion layer on the maximum impact force of granular flow,without considering the impact force distribution and the change of internal force of rock shed.In this study,the impact mechanism of granular flow and the buffering effect of the gravel cushion were studied by the laboratory model experiment,and the cushion layer made by the gravels was considered.According to the impact force distribution and the variation of the internal force of the rock shed,the impact mechanism of granular flow and the buffering effect of the gravel cushion were further explored.Then,the coupling analysis of finite difference method and discrete element in the simulation software is used to deeply explore the impact of granular flow on rock shed,and the cushion effect is explored by changing the cushion type,material and impact angle of granular flow and other working conditions.Finally,according to the damage theory,the damage analysis is carried out through the change of the structural acceleration during the impact of granular flow on the rock shed,which provides guidance and reference for the design and safety monitoring of the rock shed structure in the engineering practice.The main results and conclusions of this study are as follows:(1)The experiment of granular flow impact on shed tunnel shows that the distribution mode of impact force can be changed by adding gravel cushion on shed tunnel,besides reducing the amount of impact force.The increase of buffer layer makes the maximum normal and tangential force components shift from 0 ° to 45 °.(2)The cushion can reduce the moment and shear force,increase the axial force,and improve the structural safety of the shed tunnel.The force method is an effective method to calculate the internal force of the shed tunnel.It can quickly calculate the internal force of the shed tunnel at every moment in the process of impact.Through calculation,it is found that the maximum values of bending moment,shear force and axial force are all at 0 ° position(the arch foot on the impacted side).The maximum value of bending moment and shear force in the case of no gravel cushion is greater than that in the case of gravel cushion,while the axial force result is just the opposite.When the bending moment is small,the larger the axial force,the smaller the eccentricity,the safer the structure.(3)The numerical simulation results show that EPS cushion and gravel cushion have good buffer effect.The numerical simulation can quickly calculate the experiment of granular flow impact on shed tunnel under different working conditions.It is found that EPS cushion and fine sand cushion have good buffer effect.Shed tunnel cushion can delay the impact time of granular flow and greatly reduce the peak impact force of granular flow.During the impact process,it can be seen that the EPS cushion and the gravel cushion have obvious deformation,which means that the cushion will produce energy dissipation.(4)Based on the change of volume and displacement of plastic zone,the damage assessment method is proposed.According to the damage theory of concrete,combined with the calculation results of the number of yield elements,the acceleration and the displacement of the elements in the numerical simulation,the damage assessment method is constructed,and the damage status and the protection effect of the cushion under different sliding distance are explained.