Research On Differential Settlement And Dynamic Responses Of High Speed Railway Transition Zone Under Long-term Dynamic Load

The high-speed railway industry has gradually changed from extensive construction to high-quality operation and maintenance.The increasingly frequent maintenance of infrastructure and train safety prone-accidents have become the urgent problems.The transition zone between rigid structures and soil subgrade is the weak link of the high speed railway system.Under the long-term dynamic train load during the operation period,the uneven additional dynamic settlement will gradually accumulate and map to rail surface,which becomes the source of system excitation,intensifies the dynamic damage from train to subgrade,then threatens the driving safety.At present,the mechanism of differential subgrade settlement disease in the transition zone and the dynamic problems induced by the differential subgrade settlement are lack in-depth research.Based on the National Natural Science Foundation project,this paper studies the dynamic additional differential settlement and dynamic response characteristics of the transition zone under long-term dynamic load by using laboratory tests and numerical simulation.The main research are as follows:(1)The subgrade soil element model laboratory tests analysis on graded gravel +5% cement filling was carried out.And the vibration and deformation characteristics of the three fillers under long-term dynamic load were compared and analyzed in combination with the test results of group A and B fillers.The results show that the load level is the dominant factor to promote the growth of vertical accumulative plastic deformation,and the effect of loading frequency is slight;Under the same loading condition,the vertical cumulative plastic deformation of graded crushed stone + 5%cement filling model tends to be stable after 5000 cycles of load,and the deformation increment is significantly smaller than that of A group and B group fillers;The effect of loading frequency on vibration acceleration is significant at the higher load levels.(2)Based on the accumulative plastic deformation test data of the model test,the accumulative plastic strain calculation model was established,and related parameters of graded crushed stone + 5% cement and A group filler were fitted.Based on the condition of a subgrade-bridge transition zone of Wuhan-Guangzhou high speed railway,the simulation model of train-ballastless track-transition zone subgrade was established through SIMPACK-ABAQUS coupling method.According to the dynamic response calculation results and the accumulative plastic strain model of the two types of transition zone fillers obtained from the model test,the dynamic additional differential settlement of the transition zone after two years of operation was calculated.(3)Based on the simulation model,the dynamic responses of the transition zone after dynamic additional differential settlement were obtained,and the calculation results were compared with the situation without differential settlement.The results show that,compared with the situation without differential settlement,when the subgrade has uneven settlement,the dynamic response at each longitudinal section along the line all increase.The increment of dynamic stress at the abutment is the largest,and the increase of vibration acceleration and vibration velocity is larger in the subgrade15 m away from the abutment;Compared with the situation without differential settlement,the oscillation of dynamic stress along the longitudinal distribution has increased,and the increasing effect of train speed on vibration acceleration and dynamic stress is more significant.