Study On The Deformation Of Adjacent Existing Subgrade Caused By New High Speed Railway Subgrade Under Rainfall Conditons

Geogrid is a two-dimensional plane reinforced material.Through the embedding effect of the grid hole and the soil gravel,the friction between the grid surface and the mixture,the uneven settlement at the overlapping surface of the new and old subgrade is reduced,and the overall strength of the soil is improved.The construction time of the existing road gene is too early,the subgrade settlement grade and foundation bearing capacity requirements are low,and the materials and construction technology used are relatively backward.The old subgrade soil has basically completed the settlement consolidation,while the excavation of the new road gene construction causes the soil to loosen,resulting in differential settlement at the overlap of the new and old subgrades,causing track irregularity and affecting the safe operation of the train.In addition,environmental factors will also affect the deformation of new and old roadbeds.Rainfall intensity is one of the main influencing factors.The differential settlement of new and old roadbeds will change with different rainfall intensities.Therefore,this paper will comprehensively consider the dynamic load and rainfall,study the law of different reinforcement forms on the new and old roadbeds,and analyze the influencing factors of the deformation of the new and old roadbeds,in order to provide the optimal reinforcement scheme for related projects.Based on the project of Changjinghuang Railway(adjacent to the base section of the business line),this paper analyzes the deformation characteristics of the new high-speed railway subgrade on the existing subgrade under complex conditions by means of indoor experiment,carries out model test,and compares the real data with the data obtained by numerical simulation.The main research contents and results are as follows:(1)Taking geogrid as the research object,the coordinated deformation of the subgrade at the overlapping surface during the reconstruction and expansion of the new and old subgrades was studied through indoor model tests.When the uneven settlement of subgrade occurs under dynamic load,the relative settlement near the new subgrade is greater than that near the existing subgrade.After adding geogrid,the maximum relative settlement decreases by16.5 %,and the arrangement near the shallow layer of subgrade can better play its tensile effect.When the rainfall intensity reaches 0.01 m / h,due to the excessive rainfall,the rainwater will penetrate the entire soil,affecting the overall stability of the roadbed.Under the same rainfall intensity,the displacement of the measuring point on the subgrade slope is larger than that in the slope.With the increase of rainfall intensity,the displacement of the measuring point in the slope will also increase.(2)The model test results show that the vertical deformation and lateral deformation of the subgrade are reduced after adding geogrid.With the increase of geogrid layers,modulus and length,the increase effect is reduced.The vertical displacement of adding one layer of geogrid is reduced by 8.1 %,and the vertical displacement of adding two layers of geogrid is reduced by 11.1 %.The vertical displacement reduction range is concentrated in the 0-20 GPa geogrid,the reduction is 11 %,and the lateral displacement is 14.7 %.The 20 GPa geogrid is the best.The vertical displacement decreases by 5.7 % and the lateral displacement decreases by 21.3 % after the overall laying of geogrid,which can give full play to the deformation coordination effect of geogrid on subgrade.(3)The finite element software PLAXIS is used to establish the numerical model of the typical subgrade,and the influence of different rainfall intensity,number of layers,stiffness and length on the stability of the new and old subgrade under dynamic load is simulated.The results show that the more the number of grid layers,the larger the modulus and the smaller the subgrade settlement.The larger the length of the grid,the larger the influence area of the dynamic load on the soil,the more obvious the diffusion effect,the greater the rainfall intensity,the greater the settlement of the roadbed,and the closer the deformation to the side of the new roadbed.(4)Compared with indoor test and numerical simulation,the results show that the four variables will affect the deformation of new and old subgrade,but the effect will decrease with the increase of single variable dimension.The construction scheme of laying two layers of geogrid in the shallow layer of subgrade with elastic modulus of 20 GPa can give full play to the tensile effect of geogrid,reduce the uneven settlement of new and old subgrade,and achieve the best effect of stress diffusion.