Control Measures For Optimizing The Discharging Modes Of Rockfalls At The Last Segment Of The Guided Flexible Protection System

The guided flexible protection system is a new type of flexible protection structure that combines rockfall interception and rockfall trajectory suppression and guidance.Engineering practice reflects that the existing guided flexible protection system fails to fully consider the impact of the system structure on the discharging modes of the rockfalls.When the rockfalls are guided to the bottom of the system,there is a high probability that the rockfalls will work together with the flexible mesh and the horizontal support rope to form a "pocket effect",causing the rockfalls to be unable to be smoothly discharged from the bottom of the system.A large amount of accumulated rockfalls will not only increase the unfavorable internal force of the upper member and affect the reliability of the system,but also increase the plastic strain of the mesh,significantly reduce the impact resistance of the system,and even directly lead to the overall failure and destruction.Based on this,using methods such as component pseudo-static test,in-situ full-scale impact test,and numerical simulation calculation,the control measures for optimizing the discharging modes of rockfalls at the last segment of the guided flexible protection system was studied.Including the key parameters of the equivalent model of the annular mesh membrane unit,the numerical calculation model of the multi-body rockfallsflexible protection structure of the DEM-FEM coupling analysis,the influence law of the key parameters of the system design on the discharging modes of rockfalls,and the control measures of the rockfalls roll out speed.Finally,a set of comprehensive technical measures is proposed and optimized design is carried out in combination with actual engineering cases.The main research content and results of the thesis are as follows:(1)Carried out the bursting test of various specifications of ring mesh,revealed the threestage mechanical behavior of the ring mesh bursting process,obtained the force-displacement relationship of each specification of ring mesh;carried out the first domestic guided flexible protection system for high-position rock fall the in-situ full-scale test of the impact protection clarified the working process and dynamic response of the guided flexible protection system under the impact of a single falling rock.The results showed that the protection system successfully intercepted the falling rock.The falling rock was guided and pressed by the system on the mesh.Repeated friction and collision with the slope surface,and finally rolled out from the exit of the end of the system.The maximum internal force of all components of the system was within the safe range,and the protection system protects successfully.(2)Based on the equivalent method of the membrane element of the ring mesh,regression fitting is performed according to the model test results,the key parameters for establishing the numerical model of the ring mesh are clarified.The elastic-plastic stress-strain formula and the failure strain-mesh size relation formula of the common specifications of ring mesh equivalent membranes are proposed.The equivalent numerical model of the mesh is established.The numerical calculation results are compared with the test results.The relative errors of the bursting force,bursting displacement,and ultimate energy consumption are all within 10%.Combined with the DEM-FEM coupling calculation theory,an overall numerical model of the guided flexible protection system is established.Compared with the test results,the overall numerical model of the system can invert the whole process of the impact test.The internal force time history of each component is basically the same,and the internal force peak value is in good agreement.(3)Specific analysis is carried out on the impact of key system design parameters such as energy dissipator,steel column spacing,vertical secondary support rope spacing,horizontal support rope spacing,horizontal dense rope spacing and ring net specifications on the posture of the rockfalls.An optimization design method was proposed,and the optimization model was established for calculation verification.The results showed that the model was optimized.The rate of rockfalls valgus and jam rate are greatly reduced(both to 0,a decrease of 100%),the roll-out rate is greatly improved(up to 100%,an increase of 491.7%),all the rockfalls are rolled out,optimized the effect is remarkable,but the speed of rockfalls is increased by nearly 20%.(4)Three control measures are proposed for the derivation speed of rockfalls,and numerical models are established to calculate and verify their control effects.The results show that the three control measures can effectively reduce the roll-out speed of the rockfalls without increasing the rate of rockfalls valgus and the rate of jamming.;when the three control measures are used at the same time,the speed reduction is close to 20%.(5)Proposed comprehensive technical measures for the discharging modes of rockfalls at the last segment of the guided flexible protection system,and carried out optimized design in combination with actual engineering cases.The results show that the falling rock valgus rate is reduced by 52.3%,the jam rate is reduced by 13.4%,and the rock falling speed is reduced by9.1%.While the posture of the falling rock is significantly optimized,the speed of the falling rock is also effectively controlled.