Study On The Dynamic Properties Of Silt And Subgrade Stability Subjected To Train Moving Loading

The dynamic response of subgrade due to cyclic loading of moving train is the main reason of the deterioration of railroad.With increase in train speed,axle load and traffic weight of existing railway,the vibrations of train and track should be exacerbated, so the dynamic stress,loaded frequency,and vibration acceleration on subgrade will be grown,these should speed up the cumulative deformation and fatigue damage of subgrade.At present,there are very few studies on dynamic properties of fine-grained subgrade soils due to coupling effects of train loading increase and soil physical state changes.And there is even no special study on the deformation and strength characteristics of silt with varied compacting factor and water content,especially,the dynamic behaviors of silt under cyclic loading even has little literature.On the other hand,the effect of dynamic stress on subgrade is not be considered in the current subgrade specifications,which leads to difficult to predict the long-term effect of moving train on subgrade,in addition,there is also lack of a sound theoretical guidance system to evaluate and reinforce existing railroad subgrade,and these bring incipient faults for railway transportation.In this dissertation,silt railroad subgrade was taken as the study object,which has special characteristics and widespread distress as known.Field observations and testing results supplied the foundation to study,and according to laboratory static and cycling loading triaxial tests,theory analysis,and numeric simulation,the dynamic behaviors of silt and subgrade stability subjected to moving train loading were studied.Some achievements are as follows.(1)The properties of Yellow River alluviation silt were systemically studied. Especially,the changes of deformation and strength of this special soil with varied density and water moisture were obtained,at the same time,the subgrade distresses of railroad in Yellow River alluviation plain areas were also investigated and analyzed.(2)The dynamic deformation and strength mechanism of compacted silt with varied cyclic loading and soil physical states were apprehended,and the main controlled factors influencing the dynamic stability of compacted silt were obtained.The rules of cumulative deformation,resilient deformation,resilient modulus,threshold stress and dynamic strength of compacted silt were obtained,moreover,several prediction models about the relationships between these indices and stress and soil physical state were established.(3)The variations and expressions of wheel-track force with increasing train speed were studied by theoretical model of train-track and field observation data.After that, dynamic response of silt subgrade was simulated by tridimensional track-subgrade FEA model,and effects of axle load,train speed,and track smooth conditions were studied. During this course,the field observation results were applied to compare with calculated ones.Furthermore,effects of train axles distance,ballast thickness,material modulus and damping on subgrade dynamic response were also investigated,and significance tests of these parameters were carried out.(4)In order to consider the long-term effect of moving train loading on subgrade, two parameters,namely,dynamic strength and cumulative deformation of subgrade were selected as the controlled parameters of subgrade structure.Based on the two parameters and background of Jing-Jiu railroad,the required subgrade structures were calculated with different conditions of transportations,maintain periods,ballast thickness,and allowable settlement of subgrade,and comparisons between current specifications and the calculated subgrade structures were also done.