Abstract Summary
Technological advances in recent years have allowed the emergence of high-speed train (HST) transport. However, high speeds have the potential to cause excessive ground vibrations that can affect the track structure and the surrounding area. This can potentially cause passenger discomfort and in the worst case severe track damage. The transmission of ground vibrations from a moving train to the ground is a complex dynamic problem, which depends on various key parameters. The Quasi-static excitation, which is the dominant factor of the track response occurs due to the static component of the axle load and contributes to the lower frequency excitations. The dynamic component of the excitation, contributes to the higher frequency excitations and occurs due to the irregularities in the contact between the wheel and the rail. The dynamic excitations are involved with the far-field response. Furthermore, the ballast tracks resting on soft subgrade are difficult to meet the demands of HST due to low vertical stiffness, low shear strength and high deformability. Despite the current advances in computational engineering, the study of HST crossing regions of soft soils is still a challenge. In the present paper a numerical approach for the prediction of vibrations induced by HST is developed, verified and validated. The proposed numerical method is based on a sub-structuring approach, where first the dynamic response of the rail-track system is computed and then the wave propagation along the ground surface is calculated. The dynamic load, which is the combination of high and low frequency excitations, on the track bed is calculated using mechanical models for rail-track interactions considering the train type, speed, track structure and the properties of underground. For the low frequency component, model based on flexible beam resting on continuous spring - dashpot elements are applied in time domain. Spring-dashpot elements represents the soil dynamic properties, where the properties determined using simplified analytical calculation-cone model for heterogeneous soil. For the high frequency component, a track dynamic model is utilized. The resultant combined dynamic force consisting of the quasi-static and dynamic component due to HST transit is applied on the FEM soil dynamic model in time domain on the ballast, which is the interface of the two models. In an attempt to capture the inelastic behavior of the soil, we consider in the present study a linear-equivalent analysis based on an iterative procedure. Moreover, an iteration is also applied in order to ensure the coupling between the rail-track system with the subgrade. The computed results are verified with existing numerical results from the literature and validated with available in-situ measurements. The dynamic stability of the system is evaluated based on the computed strain level of the soil. Extensive parametric study is conducted considering material heterogeneity and variation in train speed. Critical and subcritical speeds of the train and resultant ground vibration amplification effects are thoroughly studied. All simulation results demonstrate the accuracy and the good performance of the proposed numerical approach.
