| More than two thirds of the existing ma inline railway located in seasonally frozen reigion in C hina. Affected by freeze-thaw of seasonally frozen regio n, subgrade vibration response induced by running trains are particularly sensitive. Practice and research showed that there has great influence when frozen layer thickness is greater than 0.5m, and there has serious influence when the frozen layer thickness is greater than 1.0m. Take the railway subgrade freeze-thaw disease as application background, the present thesis attempts to present relevant fundamental researches on such key issues as the dynamic performance of frozen and thawing soil, the vibration response of the subgrade, and railway embankment permanent strain. The results are presented as follows.(1) The dynamic behavior of frozen clay obtained from Beijing-Harbin railway subgrade was investigated through cryo-dynamic triaxial experiments in no rtheast of China. The effects of several key factors, including temperature, frequency and freeze–thaw cycles on the dynamic behavior, were analyzed. Conclusions were drawn as follows: reciprocal of dynamic shear modulus and dynamic strain is obviously linear relationship. Dynamic stress-strain curve can be described by the Hardin–Drnevich hyperbolic model perfectly, with negative temperature decreased and frequency increasing dynamic stress-strain curve were steeper. Freeze–thaw changes the structure of soils, dynamic stress-strain curve is great different from passing the first freeze–thaw cycles, and with the times of the freeze–thaw cycles increasing, the property is steady.(2) To investigate the dynamic characteristics of ground vibrations induced by moving vehic les in a seasonally frozen region, three field experiments were carried out in the Daqing area of C hina at various times throughout the year, in spring, summer and winter, respectively. Acceleration amplitude- frequency characteristic are influenced by train types, train load, freeze-thaw state and travel speed together. Analysis acceleration attenuation law along distance from the center of railway, and get the fitting formula.(3) A 3D finite element & infinite element model on the vibration response of the railway subgrade is established by Abaqus software, using Python compile program realize parameterization modeling. Based on typical seasonally frozen region, we established 3D temperature field calculation model which considering the phase transformation. According to statistics of the surface temperature in Daqing, and taking into the ground temperature trends, forecasting Harbin- Man zhouli railway embankment temperature distribution. O ur team’s train-track-subgrade vibration program is adopted to simulate the traffic loads to calculate track-sleeper forces, and the obtained sleeper forces are then imposed on the 3D subgrade model so that the temperature field can be coupled with the stress field.(4) Application 3D finite element model of railway roadbed in seasonally frozen region to analyze the railway embankment environmental vibration response induced by passing train in different seasons. Further research was on amplitude- frequency characteristic of dynamic stress and acceleration, and attenuation law of vibration along distance to the railway track. The effects of primary parameters such as travelling velocity, train axle, and irregularit ies of the rails are compared based on the simulation results.(5) The permanent strain model induced by long- term traffic loads of railway subgrade in seasonally frozen region was established and the model parameters obtained by the dynamic triaxial test and consolidated undrained triaxial test. The effect of train type, running speed and subgrade thickne ss on the permanent deformation induced by long- term train loads were investigated by the subgrade vibration response analysis model and temperature fie ld model. |
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