Study On Projectile Law Of Lining Fragments And Casualty Assessment In Road Tunnel Explosion Accident

Road tunnel has many advantages such as optimizing road linearity,shortening road length and releasing ground space.Based on the above,the number of road tunnels has been increasing rapidly in the process of the improvement of expressways and urban traffic in China.However,while road tunnels make travel more convenient,they also bring about various safety problems.Due to the construction and operation process of the tunnel,which is easily exposed to explosives or flammable materials,explosion accidents occur from time to time.In addition,as the throat of traffic,tunnels are also easy to become targets for terrorist attacks.Tunnel explosion accidents come along with disasters including overpressure,flame,smoke and fragments etc.In order to ensure the safety of the people’s life and property,it is necessary to conduct an in-depth and systematic study of the traffic tunnel explosion accident,so as to minimize the loss caused by the explosion accident.When there is an explosion accident in the road tunnel,the blast wave directly acts on the lining,and the lining will be broken and generate a lot of fragments.Aiming at the lining fragments generated by the breaking of the lining under the blast load,the projectile rule of the lining fragments inside the tunnel and the damaging effect of the lining fragments on the personnel are studied by combining numerical simulation and theoretical calculation.The main research contents and achievements include the following aspects:(1)The traditional erosion algorithm will cause mass loss when simulating concrete breaking under explosion load,and this defect will make reliable concrete fragments analysis impossible.In order to obtain the characteristic parameters of concrete fragments,the FEM-DEM coupling method was used to simulate the failure of concrete.Considering the strain rate effect of concrete,a rate-dependent cohesive constitutive model was proposed.Compared with the experimental results and the simulation results of erosion algorithm,it is found that the FEM-DEM coupling method combined with the rate dependent cohesive constitutive can avoid the mass loss and better simulate the break of concrete.(2)Compared with the breaking of the concrete under explosion load,the projectile process of fragments lasts longer and has a wider range.Therefore,the projectile trajectory of fragments obtained completely through numerical simulation requires too much calculation and can hardly be realized.In order to obtain the projectile trajectory of fragments more quickly,the program of fragments retrieval and rapid prediction of projectile trajectory was developed.The program can retrieve the fragments from the numerical simulation results,obtain the shape information and the initial motion state of the fragments,which make it possible to obtain the air resistance coefficient.The collision between the fragments and the inner wall of the projectile space was calculated by the rebound coefficient,which was obtained by fitting the numerical simulation results.Gravity,air resistance and Magnus force caused by rotation were considered in the calculation of the projectile trajectory.(3)After an explosion occurs in the tunnel,the air velocity inside the tunnel will be changed,greatly affecting the fragments trajectory.In order to obtain the variation law of the air velocity in the tunnel after explosion,the characteristics of the air velocity after the explosion with different explosive sources were simulated and analyzed,and a calculation model for calculating the air velocity in the tunnel was proposed.This model can calculate the curve of the average axial velocity of air on the section at a certain distance from the explosion source,which can well consider the influence of air velocity during the whole process of fragments projection.(4)Aiming at the characteristic parameters and projectile laws of the lining fragments generated after the lining of the road tunnel is destroyed under the explosion load,the FEM-DEM coupling method was used to simulate the breaking of the road tunnel lining under different explosive loads.Through the fragment retrieval program and the projection trajectory calculation program,the geometric information of all the fragments and the projection trajectory were obtained.Finally,the size distribution law,initial velocity distribution law,impact point distribution law and impact energy distribution law of lining fragments under different explosion loads were obtained.(5)In order to assess the hazards of lining fragments to people under different explosion loads,the first step was to obtain the dynamic distribution of people in the tunnel under different traffic conditions and different evacuation times through STEPS evacuation software.Then combined with the impact energy distribution of lining fragments and the criterion of kinetic energy,the casualties caused by lining fragments under different explosion loads,different traffic conditions and different evacuation times were obtained.Finally,the relationship between casualties,explosion load,evacuation time and traffic conditions were obtained.