Working Mechanism And Deformation Control Of Flexible Rockfall Barrier

The flexible rockfall barrier system is an efficient protective structure against rockfall hazards,which is widely used in the prevention of engineering geological hazards in railway,highway and other industries.In recent years,the research on flexible rockfall barrier system at home and abroad mainly focuses on the mechanical behavior of components,but the research on the buffer mechanism of the system is scarce.What’s more,the large deformation mechanism and control method of the system have not been revealed yet.Therefore,the large deformation mechanism of the flexible rockfall barrier system was deeply studied in this paper.The influencing factors of large deformation of the system were analyzed,and the composition and development of the deformation at each stage of the system were obtained.Based on this,the large deformation control equation and corresponding analytical calculation method are constructed.This method can easily realize the system selection and design.This paper established an improved system buffer mechanism,which can improve the buffer performance of the system.Then the deformation-controllable system was constructed based on analytical calculation method and the improved buffer mechanism.The full-scale test and numerical simulation were carried out to investigate mechanical behavior of the system under impact load.Finally,the relationship between the impact force F and the buffer deformation s of the system was further studied,which may provide some reference for the system design.The specific research content of the paper was detailed as follows:(1)The current situation of the flexible rockfall barrier system was studied(Chapter 1).The research status of the flexible rockfall barrier system was summarized by three parts: the mechanical properties of the components,the buffer mechanism,and the impact mechanical behavior of the system.The shortcomings of the existing research were pointed out,and the research content and the technical route of this paper were given.(2)Large deformation composition,mechanism and influencing factors of flexible rockfall barrier system were explained(chapter 2).It pointed out that the large deformation of the system is mainly composed of deformation of support structure,sliding deformation of support rope and puncturing deformation of ring net.Then the deformation of the ring net and the definition of the tensile deformation development coefficient of the ring net were described.The working principle and mechanical properties of the energy dissipating device were explained,and the tensile efficiency coefficient of the energy dissipating device was also defined.Additionally,three types of support structures commonly used in flexible rockfall barrier system were introduced.(3)The spatial geometric analytical model of the impact deformation of the flexible rockfall barrier system was constructed,and the large deformation control equation of the system was also established(Chapter 3).Analytical calculation method for deformation of support structure,sliding deformation of support rope and puncturing deformation of ring net were proposed.The analytical solution for steel wire-ring nets were validated by 17 puncturing tests and the analytical solution for system was validated by 3 different impact energies of numerical simulation model.(4)The improved buffering mechanism of the flexible rockfall barrier system was established(Chapter 4).A reasonable range of the ratio of the activation force of the energy dissipator to the breaking force of the support rope is given to ensure that the energy dissipator can work normally.The existing support rope slip control method was improved,so that the support rope can avoid the motion interference with the column end and can effectively control the impact deformation of the system.(5)The flexible rockfall barrier system with controllable deformation was constructed and full-scale test and numerical simulation were carried out(Chapter 5).Based on the analytical procedure,a prototype model of the flexible rockfall barrier system with a nominal energy level of 2000 kJ was designed.The impact mechanical behavior of the system was studied by the full-scale impact test and numerical simulation.The research results showed that flexible rockfall barrier system with controllable deformation had low internal force when subjected to rockfall impact,and there was no obvious "brake effect" inside the system,which reduced the possibility of system damage.(6)Furthermore,8 different numerical models were built to investigate influence of capacity of the energy dissipating devices on controlling of large deformation of the system(Chapter 6).The results indicated that the energy dissipating devices has the optimal stretching length and corresponding working tension to ensure the system get optimized buffering performance;The working tension of the energy dissipating devices is negatively correlated with the impact deformation of the system,but this correlation disappears when the working force exceeds a threshold.In a specific interval,the deformation of system can be adjusted by the tension of energy dissipating devices to obtain the optimal buffering performance of the system.