Mechanical Response Of The Impact Of Dry Granular Flows On Flexible Barrier

Flexible barrier have been widely used for the mitigation of nature hazards including rockfall and rock avalanche because of its high protective capability and efficient installation.However,the differences of flexible granular flow barrier between rigid wall and flexible rockfall barrier are still unclear.The empirical coefficient method is usually used for designing flexible granular flow barrier because the design theory of flexible granular barrier is still immature.In this study,the field surveys,the physical experiments and the numerical simulations are conducted to reveal the interaction between flexible barrier and granular flow firstly.Then,a simplified mechanical model to estimate the impact force of granular flow and the tensile force of flexible barrier is proposed based on the pileup characteristics of dead zone and the cable theory.Finally,the effects of the structures of flexible barrier and the physical mechanical parameters of granular flow on the estimated results are discussed.The main conclusions of this study as follows:1.The structure characteristics of flexible barriers are concluded based on the field investigations and the case studies.The flexible barriers can be installed either on the slope or in the gully.The differences between the mentioned two patterns of flexible barrier are identified when considering flow volume passing through mesh,number of ropes and installation angle of mesh.2.Estimation method for the maximum impact force of granular flow.Propose a method to estimate the maximum impact force of granular flow.The impact velocity of flow layer and the pileup height of dead zone are obtained according to the energy conservation.The critical condition of the changes in the main components of the impact force is the relationship between the critical volume of granular flow and the actual volume of granular flow.The critical pileup height and the hydro-static model could be used for the estimation of the maximum impact force.To be more precise,the empirical static coefficient should be adjusted based on the change in the main components of the impact force.3.Evaluation model for the tensile force of flexible barrier.Reveal the distribution and the main components of the impact force of granular flow against flexible barrier.The static force of dead zone is calculated using the limited equilibrium method.The difference between the maximum impact force and the static force is regarded as the dynamic impact force.Whilst dynamic impact force is categorized into three parts: the impact force transferring from dead zone to flexible barrier,the impact force on flexible barrier and the friction force between dead zone and flow layer.Finally,the tensile force of the ropes are calculated based on the distribution of the impact force on the flexible barriers and the cable theory.To verify the proposed model,the physical impact experiments of the granular flows against the vertical and tilted flexible barriers are conducted.The calculated results show essentially coincidence with the experimental results.4.Simulation for flexible barrier by using DEM model.The Hertz-Mindlin bonding particle model and the no-slip Hertz-Mindlin model is employed to simulate flexible barrier and granular flow respectively.The model validation method of the DEM contact parameters of flexible barrier is presented.The simulation results show that the DEM model can simulate the impact process effectively by the comparison of the numerical results between the small-scale experiments and the field experiments.It provides a new quantitative method to calculate the impact force of the granular flow and the tensile force of the ropes.5.The effects of rope number,size and the shape of mesh on the impact force of granular flow are revealed using the numerical and the physical experiments.From the perspective of the changes in flow states,the influences of the distributions of particles size on the flow regimes of granular flow and the tensile force of ropes are discussed.Based on these analyses,the applicability analysis of the proposed mechanical model is made.