Study On Dynamic Characteristics And Parameters Of Ballastless Track-subgrade Of High Speed Railway

With the development of high speed railway, ballastless track is widely applied in our country. But at this moment, the design of ballastless track-subgrade is usually based on experience and model-test result abroad. Research on the dynamic response of subgrade under high-speed train load and its influencing factors are still far from enough. In this thesis, based on the achievements of previous literatures, supported by scientific research fund of the ministry of railways, the dynamic characteristics of ballastless track/subgrade in high-speed railway is investigated by theoretical study, numerical simulation and model test, and large-scale dynamic triaxial tests were used to study the dynamic properties of coarse-grained soil fillings. The main research work and conclusions are listed as below:1. A dynamic analytical model of ballastless track-subgrade was established, in which the rail and ballastless track was modeled as Euler beam, fastener and CA layer were simplified to the spring-damping structure and the subgrade was regarded as homogeneous viscoelatic half-space. By mean of moving coordinate and Fourier Transform, the equations of track system and subgrade structure were established respectively and solved in the wave number domain. According to deformation compatibility conditions and IFFT algorithm, the integral expressions were calculated by numerical method. Then the influence of frequency, velocity of train, and the elastic modulus of subgrade on the displacement on the surface of subgrade were analyzed. Results show that, when velocity is less than200km/h, the vertical vibration on the surface of subgrade distributes right below the track structure, and its amplitude decreases with the increment of frequency. When velocity is larger than250km/h, the distribution of vertical vibration is not limited to the region under the track structure, and its amplitude increases with the increment of frequency. Resonance will emerge while the speed of train approaches Rayleigh wave speed.2.The results of large-scale dynamic triaxial tests indicate that dynamic strain is the most important factor affecting the dynamic modulus and damping ratio of group-B fillings. With the increase of dynamic strain, dynamic modulus decreases rapidly when dynamic strain is less than0.075%, and damping ratio increases rapidly when dynamic strain is less than0.015%. Both dynamic modulus and damping ratio increase with the enlargement of loading frequency and confining pressure. Dynamic modulus decreases with the increment of vibration number, and the reduction is more obvious under higher stress level.3.Three-dimensional dynamic finite element model of ballastless track/subgrade system was developed and validated to discuss spatio-temporal distribution law of the dynamic characteristics of subgrade. Using3D finite element model of ballastless track-subgrade, the time/space distribution of dynamic response in subgrade, and the influence of material parameters, train axle load and speed, irregularity of rail on the dynamic response of the whole system are studied. And an overall evaluation about the parameters was conducted. The influence of filling defects (insufficient compaction) and submergence were also analyzed using this model. Results show that. Filling defects have limited effect on the dynamic response of subgrade. If submergence leads to the separation between track structure and subgrade, the dynamic stress in subgrade will enlarge more than3times.4.A ballastless track-subgrade model test system was built. This system contains full scale ballastless track-subgrade model, reaction frames, dynamic loading system and data acquisition system. Depending on the test model and the diffusion path of train load, a load distribution system and corresponding loading scheme were designed. Then finite element method was employed to calculate the load-time curve of actuators which can take the additive effect of adjacent bogies into consideration. Based on the long-term observational data of subgrade settlement during different construction processes, the main rules were analyzed, and then the post-construction deformation of each subgrade layer was predicted using Kelvin model.