| Heavy-haul railway transportation is an effective way to improve railway freight capacity and an important direction of world railway freight development.The countries developing heavy haul transportation generally believe that improving axle load is one of the most effective ways to improve transportation capacity and efficiency of Heavy-haul railway.The operation of large axle load freight cars will inevitably have a greater cyclic dynamic effect on the subgrade of heavy haul railway,leading to excessive cumulative plastic deformation and even damage of the subgrade.In the loess region of Northwest China,loess Yuan,Liang and Mao are connected through ditches.There is a filling embankment-excavation transition section in the Heavy-haul Railway Subgrade of this area.Because the Loess in the excavation section is loose and collapsible,and its static,dynamic strength and structural stability are lower than that of the embankment,Therefore,the transition section between embankment and cutting will produce large differential dynamic stress,dynamic deformation and cumulative differential deformation under the dynamic load of Heavy-haul train,which will directly affect the operation safety of Heavy-haul train.In view of this,this paper relies on the subject of"Research on Key Technologies of Heavy-haul Railway Construction".By means of laboratory test,field monitoring,theoretical analysis and numerical simulation,the dynamic response law of embankment-cutting transition section of newly built standard-pond Heavy-haul Railway in loess area is analyzed,and the differential settlement development law of the transition section of embankment-cutting is deeply studied,and the corresponding settlement control method is put forward.The main research contents and results are as follows:(1)Through indoor static and dynamic triaxial tests,this paper reveals the law of dynamic strain development of lime-improved loess and compacted loess under cyclic loading.According to different dynamic stress amplitudes,confining pressures,moisture content and frequency conditions,the dynamic cumulative strain law of lime-improved compacted loess is analyzed emphatically,and suitable for new quasi-pond heavy haul railway subgrade is put forward.An integrated model for predicting cumulative deformation of layered soils.(2)In this paper,a three-dimensional dynamic finite element model of the track-cutting transition section of Heavy-haul Railway in loess region is established,and the reliability of the model is verified by field monitoring.Based on the actual working conditions,the model takes the three-dimensional viscoelastic dynamic artificial boundary as its boundary condition,uses sinusoidal wave impulse function to input moving loads and considers the pile-soil interaction,which provides technical support for the dynamic response research of embankment-cutting transition section.(3)The dynamic stress and vibration acceleration of roadbed under different axle loads and speeds were measured by field running test of embankment-transition section-cutting section of Heavy-haul railway.The results show that the influence of train axle load on dynamic response of subgrade is significant,and the influence of vehicle speed on dynamic response is limited.The attenuation rate of dynamic response of subgrade is the fastest in the surface of subgrade,and it is less affected by dynamic response below 3M of subgrade.Along the longitudinal direction of the line,the dynamic response of transition section is relatively large,and this phenomenon becomes more and more obvious with the increase of axle load.(4)In this paper,the dynamic response of embankment-cutting transition section of Heavy-haul Railway is calculated.The spatial and time-history-spectrum variation of dynamic response along the cross-section direction of the railway in the transition section of embankment under natural and composite foundation conditions is analyzed.According to different train axle load and speed conditions,the vertical dynamic stress,dynamic displacement and vibration of different structural layers in the transition section from top to bottom are expounded,and the dynamic response law of the surface layer of the subgrade under the condition of constant speed two-way turning under large axle load is revealed,which provides a theoretical basis for the design of Subgrade and subgrade structure in transition section and the analysis of cumulative deformation.(5)The relationship between train load vibration frequency and axle load variation and cumulative differential settlement of embankment-cutting is established.The influence of foundation type,train axle load and load vibration frequency on cumulative plastic deformation of embankment-cutting transition section in loess region is analyzed in depth,which provides a scientific basis for predicting differential settlement of embankment-cutting transition section in Loess Region under large axle load.(6)In this paper,a method based on geocell and geogrid combination is proposed to control differential settlement in the transition section of embankment cutting,and a method to optimize the composite foundation of lime-soil compaction piles with pile spacing as a single index is proposed,which provides a theoretical basis for the control of differential settlement in the transition section of embankment-cutting of Heavy-haul Railway in Loess region. |
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