| In the construction of infrastructure such as roads and railways in mountainous areas,frequent collapses rockfall is often accompanied,especially in the high and steep slopes along the mountain and river.Rockfall usually impacts only small area randomly,while the damage may be high with serious consequences.Besides,rockfall is difficult to accurately predict,which prompts us to pay more attention to the design of the slope protection project.This paper is based on the rockfall disaster management project of the Linjiang to Changbai road(K233+110~K233+190).Firstly,the natural geological characteristics,engineering geological characteristics and the collapse status of the dangerous rock in the study area are described.The induced factors which affect the rockfall formation were analyzed.Secondly,the probabilistic model was used to investigate the trajectory of falling fragment caused by dangerous rock.Finally,the shed structure designed in this project was taken as the model,and the process of falling rock impact reinforced concrete shed structure was carried out by FEM method.The dynamic response characteristics of the reinforced concrete shed structure under different impact speeds,impact angles and thicknesses of different sand buffer layers were studied.The research results obtained are as follows:1.The high-steep slope of the rockfall area along the Yalu River has thick layered and massive hard rock.Due to structural joints,unloading cracks and anisotropic structural planes of different sizes on the top,and the front edge of the slope,the rock mass of the high-steep slope is cut through under the gravity.The external induced factors of rockfall in the study area mainly include climate,plant,weather,unloading,and human activities.2.The results of the rockfall probability model show that the existing highways will be greatly affected by the falling fragements of the dangerous rock masses U1,U2 and U4.About 39.1%,39.9% and 23.7% of the falling blocks affect the traffic safety of the roads.The rockfall events are divided into three categories according to the kinetic energy.The dangerous rock masses U1,U2 and U4 belong to the high-intensity category.The blocks from the dangerous rock mass U3 and the collapsed C1 belong to the medium-intensity category,and the blocks from the collapsed C2 belong to the low-intensity category.3.Under the different impact speeds,the depth of the crater formed by the rockfall impact becomes deeper with the increase of the impact velocity,while the deflection of the ceiling increases gradually.The deflection curves are symmetrically distributed,and the stress curves of the ceiling are also basically symmetrical distributed.4.Under the different impact angles,the normal impact force is at least 42% larger than the tangential impact force.So the normal impact force is only considered during the calculation of the impact force in actual engineering project.As the impact angle increases,the normal impact force decreases continuously,while the tangential impact force increases first and then decreases,reaching to maximum at 45°.It is manifested in the shape of the crater of the sand buffer layer through the following phenomenon.The side of the craters rise with the increase of the impact angle,and the maximum bulge height first increase and then decrease,and reach to the highest bulge at 45°.5.Under the different soil thicknesses,the impact contact force between the ceiling of the shed and the buffer tends to decrease with time.The maximum impact contact force decreases as the thickness of the buffer layer increases,and the slope of the fitted curve of the maximum impact contact force also decreases.At the same time,the deflection of the ceiling is continuously reduced with the thickening of the buffer layer,and the amplitude of the deflection is also reduced.Based on the Guidelines for Design of Highway tunnel,the appropriate thickness of soil is 1.5 m. |
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