Research On The Reinforcement Mechanism And Effect Of Existing Railway Subgrade By Trenchless Rotary Grouting

In recent years,with the increase of the operating mileage of high-speed railways and the formation of networks,more existing lines will be put into freight transportation.Relative to passenger transport,freight transport trains are with the greater axle load and more pronounced impact on subgrade beds.But at present,there is no suitable reinforcement method on busy lines.As to existing railway subgrade diseases,it has proposed a method for reinforcement of trenchless rotary grouting of railway subgrade.This method utilizes the advantages of trenchless guide hole forming technology and hole-in-hole rotary spraying technology.With the features of small construction disturbances,long reinforcement distances and so on,this method has a wide application prospect.However,at present,there is a lack of theoretical research and engineering examples for the reinforcement technology.The effect of the reinforcement construction process on the subgrade and the track structure is not yet clear,and the jet grouting pile arrangement method and reinforcement effect are not clear.Therefore,it is of great significance to study the reinforcement mechanism and reinforcement effect of the trenchless rotary grouting reinforcement method for railway subgrade.This paper takes the existing railway subgrade as the research object,based on the theory of car-track-road coupling dynamics,a finite element software ABAQUS is used to establish a coupled dynamic analysis model for train-track-subgrade and added-solid space.This model can be used to analyze and simulate actual trenchless and inner hole spinning processes.This paper first explores the shallow railway subgrade with long distance vertical grouting reinforcement method.The effect of the construction process on the existing track structure is analyzed and the appropriate parameters are discussed.At the same time,the paper also discussed the reinforcement effect of the subgrade under different layout of the rotary jet pile.The main research work and results are as follows:(1)Create a numerical simulation analysis model of railway subgrade non excavation grouting reinforcementFor railway subgrade non excavation grouting reinforcement technique,the paper establishes the subgrade non excavation guide hole model,the inner rotary jet model of the foundation bed and the dynamic analysis model of the train track subgrade and the solid space coupling by using the finite element software.The model utilizes the "Life-Death unit" technique and the pore-pressure boundary theory of porous media to simulate the construction process of trenchless rotary spraying.The paper try to calculate the reasonable mesh size of the model,and compare the numerical simulation results with the field test values to verify the accuracy of the model.(2)Study of the mechanism of trenchless drillingThrough the establishment of the mechanical analysis model of the guide bit in the drilling process,the key parameters determining the drilling efficiency are determined.The Influence of trenchless construction on existing track subgrade structure and the impact of inner guide hole wall in the subgrade are analyzed by using theoretical derivation and numerical simulation methods.The analysis results show that,the maximum vertical displacement of the road base surface during the process of trenchless construction is 0.192mm.Meanwhile,the maximum vertical displacement of the rail does not exceed 0.01mm,so trenchless construction in the busy existing mainline subgrade will not affect the train operation.(3)Research on the mechanism of hole spinningThe paper describes the shallow subgrade hole jet theory and analyzes the softening effect of rotary jet by using the rotary jet grouting model.Also,the suitable parameters of rotary jet grouting in railway subgrade are also discussed.The calculation results show that when the grouting pressure is less than 20Mpa,the static safety index of the track structure and the dynamic safety index of the train are not limited.It is suggested that the grouting pressure in the shallow subgrade should not be greater than that of 20Mpa.(4)Analysis of the effect of horizontal jet grouting pileBased on the theory of horizontal ground beam and the finite element dynamic analysis model,the reinforcement mechanisms of horizontal piles in the railway subgrade are analyzed.The effect of subgrade reinforcement under different arrangement of piles and the effect of the reinforcement method on the stress,deformation and vibration of subgrade structure are studied.the study on the effect of rotary jet reinforcement shows that the longitudinal jet grouting pile could effectively control the vertical displacement of railway subgrade.in which the reinforcement effect is obvious in the bedding-surface,and after the reinforcement,the vertical displacement of the subgrade surface is reduced by 41.2%.The dynamic stress of the subgrade surface would be increased after reinforcement,but,due to the jet grouting pile,the ratio of dynamic stress to material strength has been increased.So the overall subgrade structure of the force has improved.Above all,the analysis results show that trenchless rotary grouting is an effective method of subgrade reinforcement and it is suitable for the rapid reinforcement of existing railway lines under the operating conditions.