Study On Mud Characteristics Of Railway Subgrade And Mechanism Of Intrusive Ballast Under Hydrothermal Action

With the increase of traffic volume and load,railroad diseases have emerged,of which the mud pumping as one of the most common diseases,has aroused widespread concern.Slurry mud is the phenomenon that the subsoil is affected by natural rainfall and groundwater migration,and the soil is softened or liquefied to form mud under the action of train load,which gushes upward along the ballast voids.The mud pumping make the ballast layer contaminated and uneven foundation settlement,which seriously affects the safety and stability of train operation.Based on the above problems,this thesis analyzes the characteristics of the mud formed by the subsoil,the start time of mud invasion into the ballast,the dirty ballast after invasion,the seepage path and the seepage speed after the invasion of different characteristics of mud into the ballast,in combination with the filler and environmental factors of heavy haul railways.The following conclusions were drawn.(1)Mud viscosity,density and water loss were identified as the main indicators for assessing mud characteristics;combining the physical properties of the soil with the parameters of mud characteristics,it can be obtained that silt and silt-clay are more prone to overturning and mud pumping when used as subgrade soil.(2)Through the test of mud pumping on different types of subsoil,the changes of hydrodynamic water pressure,ballast settlement and intrusion were analysed.The study shows that no mud formation in the saturation process;during the loading process,the silt-clay has a higher clay content,the pore water pressure accumulates more rapidly,giving priority to the formation of mud,the degree of pumping is also more intense,the ballast settlement is more significant,and the ballast is more seriously dirty.(3)Due to the presence of permafrost nuclei in the bed during thawing,the mud overturning phenomenon in the bed after freeze-thawing is more gentle than in ambient conditions,and the mud intrusion height is lower;water migrates upwards during freezing,and the cumulative settlement of ballast after freeze-thawing is greater than that of ballast in ambient conditions.(4)Using industrial CT scan ballast to determine the basic representative unit,combined with the mud characteristics parameters to simulate the mud in the ballast found that the greater the viscosity of the mud,the smaller the percolation rate in the ballast,and the greater the viscosity,the mud adsorbed on the ballast surface,rising slowly,layer by layer to fill the ballast pores,so the preferential percolation path is not obvious;the smaller the viscosity of the mud,the faster the percolation rate in the ballast,the mud preferential migration path is more clear.(5)The preferred seepage path of the mud is mainly through the large pore size pore space,isolated and small pore space seepage is relatively insignificant.The flow rate is significantly higher in the connected large pore size pores than in the unconnected fine pore size pores and isolated pores.