Research On Mechanics Characteristic Of Ballast-polyurethane Based On Tests And Simulation

Polyurethane with its good-function can be act as a kind of track reinforcement material,and already widely used in ballasted track bed.The usage of polyurethane including stiffness adjusting in transition zone,ballast flight prevention,curve sections reinforcement,etc.ballast track with polyurethane reinforcement performed as a new kind of track system has shown its vigorous vitality and broad application prospects.However,with the application of polyurethane reinforcement,more and more problems occurred with the current polyurethane method.At this stage,polyurethane material has a high strength,and spraying method lets the whole ballasted bed bonding together,daily maintenance method such as tamping cannot be carried.Aiming to solve the problem mention above,this thesis focuses on polyurethane reinforcement special for high-speed railway.This research produced 5 kinds of polyurethane cooperating with Special Waterproof Material National Key Laboratory,and put forward 2 reinforcement method including full-section reinforcement method and specific-section reinforcement,and the latter includes shoulder reinforcement,crib reinforcement and synthetical reinforcement(both shoulder and crib),all these methods do not influence tamping maintenance.Test and modeling are used in this thesis,track bed resistance test,uniaxial unconfined compression test,wind tunnel test and tamping test are performed to reveal the reinforcement effect,ballast flight prevention effect,reinforcement characteristics and tamping availability,at the same time,this result is used for polyurethane selection thus get the best kind.In addition,simulation based on DEM is carried out,analyzing the micro behaviour of ballast-polyurethane.The main conclusion of this research is as follows:1.Ballasted bed resistance(1)Results show that after spraying type-1 to type-5 polyurethane,the longitudinal resistance can increase 6-16%,the lateral resistance can increase 9-17%.Due to the low strength and depth,the increase ratio of resistance is not significant.(2)When using type-4 polyurethane with specific-section reinforcement method,the lateral resistance increases 41%-184%comparing with the ballasted bed before reinforcement,the effect is significant,and with its wide range,this method specially fit railway construction.2.Optimal polyurethane selection(1)According to tamping tests,after type-1 to type-3 polyurethane reinforcement,tamping does not show any difficult,type-4 also performs its availability with slightly more difficult.However,type-5 can do tamping,but the bonding around tamping hole is broken.(2)This research builds a 1:1 half structure model in wind tunnel with type-1(which with the minimum strength)polyurethane reinforcement,results show,no ballast displacement occurred.(3)According to uniaxial unconfined compression tests,type-4 polyurethane-ballast cubic specimen has better strength-deformation characteristics.Type 4(14.2Mpa,elongation at break 20%,shoreD 46)is the optimal selection.3.Mrico analysisAccording to simulation results,in flat shoulder ballasted bed lateral resistance,shoulder contributes the most part and crib with the least ratio.The force-chain shows that the uniformity of contact force at a bad condition,stress concentrates in some particles.After full-section reinforcement,surface ballast bears a part of contact force,because of the low reinforcing depth,the increase is not apparent.After shoulder reinforcement,shoulder ballast acting as a whole contributes more resistance which has a widely spread and balance contact force.Crib reinforcement lets the sleeper-ballast contact at crib not only in friction but also compression and shear,3 parts of contribution ratio nearly the same.Synthetical reinforcement which combines shoulder and crib reinforcement has the biggest increase and widest force spread area.