Research On The Motion Characteristics Of Rockfall And Dynamic Response Of Rock-shed

The quantitative prediction and evaluation of rockfall disasters in mountainous areas can not only provide specific and intuitive parameter information for the design and deployment of rockfall disaster prevention engineering measures,but also provide reliable technical support for the site selection of towns and routes,and the delineation of risk areas.So it has important significance.While single evaluation method and less evaluation factors considered resulting in the calculation or prediction results are often too conservative,and they are quite different with the actual results in the evaluation of the rockfall disaster.To this end,this paper studies the distribution,origins and type of unstable rock mass in the Jiufengshan section of the"Hebijin"expressway under construction through field survey.And carry out the model test of rockfall movement and its impact to the rock-shed sand cushion to verify the numerical calculation model.Constructing the research system of rockfall movement and impact process and be used to study the rockfall disaster of slope with unstable rock mass in the study area.Computational evaluation research.The results of the paper are as follows:(1)Identify the development characteristics of unstable rock mass in the study areaThe stratum in the study area is mainly sand and mudstone interbedded,and much unstable rock mass is formed under the action of differential weathering,rainfall,human engineering disturbance and other factors,including:"separate","toppling"and"suspended",which threaten the study area The main construction of the internal line is"separate"unstable rock mass with a maximum diameter of 250cm,which is widely distributed on the side slope of the line,with a total volume of 35,000to 46,000m~3,and the potential main collapse direction is the location of the line.(2)Propose the analysis method of rockfall from motion to impactComparing the model test on the characteristics of the rockfall,the discrete element method is used to study the motion process of the rockfall,and this method is used to simulate the motion process of rockfall on a slope.The results show that the speed of the rockfall is affected by its shape.The closer the rockfall is to the spherical shape,the faster the speed of the rockfall is.In the simulation,the speed of the spherical rockfall can be faster about 30%compared with the strip-shaped under the same diameter.The discrete element-finite difference coupling method is adopted,in which discrete elements are used to simulate the discrete type of sand cushion,and the finite difference method is used to simulate the continuity of the shed structure.With the advantages of the two simulation methods,the dynamic response of the rock-shed structure under the impact of the rockfall is studied.Comparing the physical model test proves the feasibility of the method,and on this basis,the process of impacting the sand cushion of the rock-shed at different speeds and angles is studied.Through the analysis of the process of rockfall movement and impacting sand cushion,a research system of rockfall movement-impacting process is constructed.(3)Taking slope with unstable rock mass in the study area to research the rockfall motion and impact process.Select a slope with unstable rock mass in the study area,and carry out a case study of the rockfall motion-impact process.The simulation analysis is carried out according to the maximum diameter of the rock,and the results show that the maximum movement rate of the potential slope rockfall is about 20m/s and the impact energy is nearly 900k J.Considering the site conditions,it is recommended to use the rock-shed as a prevention method.According to the analysis of the movement of the rockfall on the slope,the thickness of the cushion is set to be 1?3m,the density is1600?2400kg/m~3,and the simulation study of the rock impact on the shed structure is carried out.The results show that under this impact energy,sand cushion with thickness of 1m and density of 1600kg/m~3 can have a better cushioning effect.Increasing the thickness or density of the cushion can reduce the impact force of the rockfall to a certain extent,but it will significantly increase the weight of the structure.Therefore,in engineering practice,the selection of the sand cushion should be the optimal cushion within the guaranteed impact energy level thickness...