| In order to solve the problem of rockfall disaster in tunnel entrance section,one method is to intercept the rockfall through shed and passive flexible barrier.This method has achieved good interception effect,but this kind of passive protection method is easy to cause rockfall accumulation,there are problems such as difficulty in rockfall cleaning and high maintenance cost in the later period.The other is to reinforce rock mass,although such protection method can prevent rockfall disasters to some extent,but its environmental impact is irreversible.Based on this,this paper studies a new type of flexible diversion guide structure.Based on the concept of flexible protection,the system can effectively intercept the rockfall by reasonable arrangement.on the other hand,the problem of rockfall cleaning is avoided by planning the trajectory of rockfall,and the environmental impact is small.In order to study the mechanical behavior of flexible diversion guide structure under rockfall impact and the diversion capacity of flexible diversion guide structure,this paper systematically studies the flexible diversion guide structure by theoretical derivation,full-scale test and numerical calculation.The main work and conclusions include:1.The composition and working mechanism of the flexible diversion guiding structure were expounded.After the rockfall contact net,due to the flexible buffer of the net,the rockfall speed gradually decreases.At the same time,due to the setting of a certain gradient of the net,the rock moves on the net and gradually deviates from the original trajectory.Finally,the rock is guided at a low speed to collect in the safe area to realize diversion and guidance.LS-DYNA is used to simulate the flexible diversion guide structure of rockfall group impacting triangular net and quadrilateral net.The diversion effect of the flexible diversion guide structure is measured by defining the penetration area and the penetration percentage.The results showed that flexible diversion guide structure with quadrilateral net has 0 % penetration percentage under two working conditions,and flexible diversion guide structure with triangular net has 5 %and 10 % penetration percentage under two working conditions.(Chapter 2)2.Based on the D ’ Alembert principle,the trajectory of rockfall on the flexible shunt guide structure was theoretically deduced.Firstly,the simplified model of two-dimensional trajectory was established,and the exact solution of two-dimensional trajectory,the Maclaurin series solution and the related approximate solution were obtained.On this basis,the approximate solution of three-dimensional trajectory was obtained.Based on the approximate solution,the relationship between the diversion effect of diversion guide structure and the parameters in three-dimensional case was discussed.The feasibility of the simplified model was verified by compiling the central difference calculation program of three-dimensional trajectory,and the equivalent stiffness coefficient was calculated by numerical method.(Chapter 3)3.Full-scale impact test of flexible diversion guiding structure was carried out.The results showed that the flexible diversion guide structure can be divided into the characteristics of interception stage and diversion stage.In the interception stage,it is mainly reflected in the decrease of rock speed,the rebound of the net,the elongation of brakes,and the change of the direction of rockfall speed,and then entered the diversion stage.In this stage,the rockfall mainly moved along the net panel,and was directed to divert to a safe area.(Chapter 4)4.LS-DYNA was used to establish a numerical calculation model of the flexible diversion guide structure,and the whole process numerical calculation of the flexible diversion guide structure was carried out.The results showed that the impact force received by the structure reached the maximum at the end of the interception stage,and the reduction The elongation of the brakes mainly occurs at this stage.In the whole process,the energy consumption of the brakes accounts for 40%-50% of the total energy consumption of the structure.The difference between numerical simulation trajectory and experimental trajectory measured by Euclidean norm is 0.32 m,and the difference between theoretical trajectory and experimental trajectory is0.44 m.The results show that the finite element results,experimental results and theoretical results are in good agreement.(Chapter 5)5.Based on LS-DYNA and the experimental model,a parametric analysis of the diversion capacity of the flexible diversion guiding structure was carried out.The research parameters include the lateral gradient,the longitudinal gradient,the mesh size and the wire rope diameter of net.A total of 78 were established.A finite element model was used to measure the diversion capacity by defining the final deviation ratio.The results show that the final deviation ratio increased with the increase of the lateral gradient,and when the lateral gradient was about 45°,the separation guidance effect is better.As the longitudinal gradient increased,the final deviation ratio decreases linearly.When it was less than 20°,there will be rocks remaining in the net.It was recommended to set the longitudinal gradient to 20°.As the wire rope diameter of net increased,the final deviation ratio decreased inversely,and the maximum impact displacement linearly decreased.As the mesh size increased,the final deviation ratio linearly decreased,and the maximum impact displacement linearly increased.The order of the influence of each parameter on diversion capacity was from large to small: lateral gradient > longitudinal gradient > mesh size > wire rope diameter of net.(Chapter 6)... |
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